Due to time constraints, the original draft of this document was
rushed to meet the publication deadline of the June 2000 Pittsburgh
meeting. Since the meeting has passed, we do not wish to
substantially revise the findings within this document, so that we
don't give the appearance of changing information after the
presentation. Only additional descriptions of the process,
formatting, layout editing and errors of fact have been corrected in
subsequent revisions.
After the AAA WG re-charter was approved, and the Network Access
Requirements document passed AAA WG Last Call, a Solicitation of
Protocol Submissions was issued on 4/13/2000. The Solicitation was
sent to the AAA WG mailing list, as well as to other IETF WG mailing
lists related to AAA, including NASREQ, Mobile IP, RAP, and SNMPv3.
Submissions were solicited effective immediately. Authors of
candidate protocols were requested to notify the AAA WG chairs of
their intent to submit a candidate protocol. It was suggested that
this notification be sent by May 1, 2000.
Protocol submissions and compliance description documents were to be
submitted in Internet Draft format by email to internet-
drafts@ietf.org. The deadline for submissions was June 1, 2000. To
be considered as a candidate, submissions needed to include an
unqualified RFC 2026 statement, as described at:
http://www.ietf.org/Sec10.txt
In order to assist the AAA WG in evaluating the protocol submissions
and compliance description documents, the AAA WG chairs then formed
an evaluation team, which was announced on May 20, 2000. The job of
the team was be to put together an Internet Draft documenting their
evaluation of the protocol submissions. The goal is to have a first
draft available prior to the July 14, 2000 submission deadline for
IETF 48.
In composing the evaluation draft, the evaluation team was asked to
draw from the protocol specifications, the compliance descriptions,
and other relevant documents, the Network Access Requirements
document, RFC 2989.
Mike St. Johns was asked to chair the evaluation team. The chairs of
WGs related to AAA were also invited to join the team. These
included Dave Mitton, co-chair of NASREQ WG, Basavaraj Patil, co-
chair of Mobile IP WG, and Mark Stevens, co-chair of the RAP WG.
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Additional members of the evaluation team were chosen to represent
the interests of network operators as well as developers of AAA
client and server software.
As usual, the IESG advised the evaluation team. IESG advisors
included Randy Bush and Bert Wijnen, Directors of the Operations and
Management Area.
This document is the result of 6 weeks of intense work by the panel
listed below. Our mission was to evaluate the various AAA proposals
and provide recommendations to the AAA working group and to the IESG
on the viability of each of the proposals.
The evaluation process had three distinct phases. 1) Validate the
AAA requirements document [AAAReqts] against the base requirements
documents for NASREQ, MOBILEIP and ROAMOPS. 2) Evaluate each of the
SNMP, Radius++, Diameter and COPS proposal claims against the
validated requirements. 3) Provide final recommendations based on
side by side comparison for each proposal on a requirement by
requirement basis.
In general, the ONLY information the evaluators were allowed to use
throughout the process was that provided in the source documents (the
requirements document and the proposal) or documents referenced by
the source documents. In other words, if it wasn't written down, it
generally didn't exist. Our cutoff for acceptance of information was
1 June 2000 - any submissions after that time were not considered in
the panel's deliberations.
The group was chaired by Michael St.Johns. David Mitton was the
document editor. Following are the background statements and any
conflicts of interest from them and the rest of the panel.
Michael St. Johns, Rainmaker Technologies
I have no known conflicts of interest with respect to the AAA
process. I have neither advocated nor participated in the creation
of any of the submissions. My company is a service company (ISP) and
will not be involved in the manufacture or sale of AAA enabled
products. Other than my participation as the chair of the AAA
evaluation process, I have not had any contact with the AAA standards
process.
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David Mitton, Nortel Networks
I have been Nasreq WG co-chair and author of several Nasreq drafts.
As well as, previously contributed to several RADIUS drafts.
I have been a RADIUS NAS implementor and Technical Prime on our
Server products, so know it extremely well. In my current job role I
am involved with Nortel's IP Mobility products, which support
Diameter.
I have written a presentation on COPS vs NASreq Requirements for a
Nasreq meeting, but have not implemented it, nor consider myself an
through expert on the subject.
Stuart Barkley, UUNET
I've been working for 5 years at UUNET on various parts of our dialup
network. I have extensive experience with designing, developing and
operating our SNMP based usage data gathering system. I've also been
involved in our radius based authentication and authorization systems
in an advisory position.
I've participated in radius/roamops/nasreq/aaa groups for the past
several years. I'm not an author or contributer on any of the
requirements or protocol documents being presented although I have
been peripherally involved in these working groups.
Dave Nelson, Enterasys Networks
Very active in the RADIUS WG, especially during the early years. No
involvement in the AAA submission. Have not contributed to the
development of Diameter.
No involvement with SNMPv3 or the AAA submission. David Harrington,
a proponent, works in a different group within my company. We have
not discussed the submission. No involvement with the COPS protocol.
Basavaraj Patil, Nokia
I am a contributor to the AAA requirements document (RFC 2977)
submitted by the Mobile IP WG. I was a member of the team that was
constituted to capture the Mobile IP requirements for AAA services.
As part of the co-chairing activity of the Mobile IP WG I have
realized the need for AAA services by Mobile IP and hence closely
followed the work done in the AAA WG, RADIUS, RoamOps and TR45.6.
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My present work at Nokia does involve looking at AAA protocols (to
some extent at least) for use in wireless networks. I have also done
some work with AAA protocols such as Diameter in my previous job at
Nortel Networks.
Mark Stevens, Ellacoya Networks
I am the co-chair of the IETF RAP working group which is the working
group that has developed the COPS protocol. I have not contributed
to the documents describing how COPS can satisfy AAA requirements.
I participated in early AAA working group meetings, but have not been
an active participant since the group's rechartering. The company
that currently employees me builds devices might benefit from being
AAA enabled.
Barney Wolff, Databus Inc.
I have implemented RADIUS client, proxy and server software, under
contract to AT&T. That software is owned by AT&T and I have no
financial interest in it.
I have been a member of the RADIUS WG for several years, and consider
myself an advocate for RADIUS against what I consider unjustified
attacks on it.
I've never worked for any of the companies whose staff have produced
any of the proposals, although I obviously might at some future time.
For each of the base requirements documents, the chair assigned a
team member to re-validate the requirement. The process was fairly
mechanical; the evaluator looked at what was said in [AAAReqts], and
verified that the references and supporting text in the basis
document supported the requirement in [AAAReqts] as stated. Where
the reference was wrong, too general, missing or otherwise did not
support the requirement, the evaluator either deleted or downgraded
the requirement. The results of that process were sent to the AAA
mailing list and are also included in this document in the
appendixes. The group's used [AAAReqts] as modified by our
validation findings to evaluate the AAA proposals.
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For each of the four proposals, the chair assigned two panel members
to write evaluation briefs. One member was assigned to write a 'PRO'
brief and could take the most generous interpretation of the
proposal; he could grant benefit of doubt. The other member was
assigned to write a 'CON' brief and was required to use the strictest
criteria when doing his evaluation.
Each brief looked at each individual requirement and evaluated how
close the proposal came in meeting that requirement. Each item was
scored as one of an 'F' for failed to meet the requirement, 'P' for
partially meeting the requirement, or 'T' for totally meeting the
requirement. The proposals were scored only on the information
presented. This means that a particular protocol might actually meet
the specifics of a requirement, but if the proposal did not state,
describe or reference how that requirement was met, in might be
scored lower.
The panel met by teleconference to discuss each proposal and the PRO
and CON briefs. Each of the briefers discussed the high points of
the brief and gave his summary findings for the proposal. We then
discussed each individual requirement line-by-line as a group. At
the conclusion, the members provided their own line-by-line
evaluations which were used to determine the consensus evaluation for
the specific requirement relative to that proposal. The meeting
notes from those teleconferences as well as the individual briefs are
included in the appendixes.
The panel met for one last time to compare the results for the four
proposals and to ensure we'd used consistent evaluation criteria. We
did a requirement by requirement discussion, then a discussion of
each of the protocols.
The final phase was for each member to provide his final summary
evaluation for each of the protocols. Each proposal was scored as
either Not Acceptable, Acceptable Only For Accounting, Acceptable
with Engineering and Fully Acceptable. Where a proposal was
acceptable with engineering, the member indicated whether it would be
a small, medium or large amount.
It should be noted that score indicated the opinion of the team
member. And they may have taken into consideration background
knowledge or additional issues not captured in the minutes presented
here.
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Each member's scores were used within the group to develop the
group's consensus.
The following proposal documents were submitted to the AAA WG for
consideration by the deadline.
- SNMP:
[SNMPComp] "Comparison of SNMPv3 Against AAA Network Access
Requirements", Work in Progress.
- RADIUS Enhancements:
[RADComp] "Comparison of RADIUS Against AAA Network Access
Requirements", Work in Progress.
[RADExt] "Framework for the extension of the RADIUS(v2)
protocol", Work in Progress.
- Diameter
[DIAComp] "Comparison of Diameter Against AAA Network Access
Requirements", Work in Progress.
- COPS for AAA:
[COPSComp] "Comparison of COPS Against the AAA NA Requirements",
Work in Progress.
[COPSAAA] "COPS Usage for AAA", Work in Progress.
For each requirement item, the group reviewed the proposal's level of
compliance. Where the proposal was lacking, the evaluators may have
made supposition on how hard it would be to resolve the problem. The
following shows the consensus results for each requirement item.
Key:
T = Total Compliance, Meets all requirements fully
P = Partial Compliance, Meets some requirements
F = Failed Compliance, Does not meet requirements acceptably
Where two are shown eg: P/T, there was a tie.
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The sub-section numbering corresponds to the requirements document
section and item numbers. This relative numbering was also used in
the Protocol Position presentations, here in the appendices.
3.1.1 Scalability - SNMP:P, RADIUS:P, Diameter:T, COPS:T
SNMP was downgraded due to a lack of detail of how the current agent
model would be adapted to a client request based transaction. The
RADIUS proposal did not address the problem adequately. There are
open issues in all proposals with respect to webs of proxies.
3.1.2 Fail-over - SNMP:P, RADIUS:P, Diameter:P, COPS:T/P
The group particularly noted that it didn't think any protocol did
well in this requirement. Insufficient work has been done to specify
link failure detection and primary server recovery in most
submissions. COPS has some mechanisms but not all. How these
mechanisms would work in a web of proxies has not been addressed.
3.1.3 Mutual Authentication - SNMP:T, RADIUS:T/P, Diameter:T, COPS:T
Many of the submissions missed the point of the requirement. There
should be a way for the peers to authenticate each other, end-to-end,
or user-to-server. However, the group questions who really needs
this feature, and if it could be done at a different level.
Mutual authentication in RADIUS is only between hops.
3.1.4 Transmission Level Security - SNMP:T, RADIUS:P, Diameter:T,
COPS:T
All protocols have methods of securing the message data.
3.1.5 Data Object Confidentiality - SNMP:P, RADIUS:P, Diameter:T,
COPS:T
This requirement usually comes from third-party situations, such as
access outsourcing.
Diameter and COPS both use CMS formats to secure data objects. The
group is concerned if this method and it's support is perhaps too
heavy weight for NAS and some types of edge systems.
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3.1.6 Data Object Integrity - SNMP:F, RADIUS:P, Diameter:T, COPS:T
How to guard the data object from changes was not adequately
described in the SNMP proposal. The RADIUS solution was not very
strong either.
3.1.7 Certificate Transport - SNMP:T, RADIUS:T, Diameter:T, COPS:T
All protocols can figure out some way to transport a certificate.
3.1.8 Reliable AAA Transport - SNMP:P, RADIUS:P, Diameter:T, COPS:T
The requirement does not give a definition of "how reliable" it must
be.
The SNMP and RADIUS proposals lacked in providing solutions to
message retransmission and recovery.
3.1.9 Run over IPv4 - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.1.10 Run over IPv6 - SNMP:P, RADIUS:T, Diameter:T, COPS:T
The SNMP proposal indicated that this area is still in the
experimental stages.
3.1.11 Support Proxy and Routing Brokers - SNMP:F, RADIUS:P,
Diameter:T, COPS:P
The SNMP proposal did not address this requirement. COPS claims
support, but does not work through some of the issues. Diameter was
the only protocol that attempted to address this area to a fair
extent.
3.1.12 Auditability - SNMP:F, RADIUS:F, Diameter:T, COPS:P
We treated this requirement as something like "non-repudiation".
There is a concern that digital signatures may be too computationally
expensive for some equipment, and not well deployed on those
platforms.
The SNMP and RADIUS proposals did not attempt to work this
requirement. COPS suggests that a History PIB will help solve this
problem but gives no description.
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3.1.13 Shared Secret Not Required - SNMP:P/T, RADIUS:T, Diameter:T,
COPS:T
The requirement is interpreted to mean that any application level
security can be turned off in the presence of transport level
security.
Pretty much every protocol can use an enveloping secure transport
that would allow them not to use an internal secret.
3.1.14 Ability to Carry Service Specific Attributes - SNMP:T,
RADIUS:T, Diameter:T, COPS:T
3.2.1 NAI Support - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.2.2 CHAP Support - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.2.3 EAP Support - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.2.4 PAP/Clear-text Passwords - SNMP:T, RADIUS:T, Diameter:T,
COPS:T
The requirement for clear-text passwords comes from one-time-password
systems and hard-token (SecurID) systems.
3.2.5 Reauthentication on demand - SNMP:T, RADIUS:P, Diameter:P,
COPS:T
To supply this, the proposal must have asynchronous peer-to-peer
capabilities, and there must defined operation for such state
changes.
We also distinguished event-driven Reauthentication from timer-driven
(or lifetime-driven). Also concerned about how this would work in a
proxy environment.
3.2.6 Authorization w/o Authentication - SNMP:P, RADIUS:T/P,
Diameter:T, COPS:T
This requirement really means authorization with trivial
authentications (e.g. by assertion or knowledge).
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3.3.1 Static and Dynamic IP Addr Assignment - SNMP:P/F, RADIUS:T,
Diameter:T, COPS:T
There is difficulty in interpreting what is static or dynamic with
respect to the viewpoint of the client, server, administrator or
user.
3.3.2 RADIUS Gateway Capability - SNMP:P, RADIUS:P, Diameter:T/P,
COPS:P
It was noted that any new capability in a new AAA protocol would not
be able to map directly back to RADIUS. But this is already a
problem within a RADIUS environment.
3.3.3 Reject Capability - SNMP:T/P/F, RADIUS:T, Diameter:T, COPS:P
3.3.4 Preclude Layer 2 Tunneling - SNMP:F, RADIUS:T, Diameter:T,
COPS:T
3.3.5 Reauthorization on Demand - SNMP:P/F, RADIUS:P, Diameter:T/P,
COPS:T
Some evaluators wondered how the server will know that re-
authorization is supposed to be done? Will it interface to something
external, or have sufficient internals?
3.3.6 Support for Access Rules & Filters - SNMP:P, RADIUS:P,
Diameter:P, COPS:T/P
Only the Diameter proposal actually tackled this issue, but the group
felt that the rules as designed were too weak to be useful. There
was also concern about standardizing syntax without defining
semantics.
3.3.7 State Reconciliation - SNMP:F, RADIUS:P/F, Diameter:P, COPS:T/P
All of the protocols were weak to non-existent on specifying how this
would be done in a web of proxies situation.
3.3.8 Unsolicited Disconnect - SNMP:T, RADIUS:P, Diameter:T, COPS:T
3.4.1 Real Time Accounting - SNMP:T, RADIUS:T, Diameter:T, COPS:T
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3.4.2 Mandatory Compact Encoding - SNMP:T, RADIUS:T, Diameter:T,
COPS:T
3.4.3 Accounting Record Extensibility - SNMP:T, RADIUS:T,
Diameter:T, COPS:T
3.4.4 Batch Accounting - SNMP:T, RADIUS:F, Diameter:P, COPS:P
Some members of the group are not sure how this fits into the rest of
the AAA protocol, which is primarily real-time and event driven.
Would this be better met with FTP?
3.4.5 Guaranteed Delivery - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.4.6 Accounting Timestamps - SNMP:T, RADIUS:T, Diameter:T,
COPS:T
3.4.7 Dynamic Accounting - SNMP:T, RADIUS:T, Diameter:T, COPS:T
3.5.1 Encoding of MOBILE IP Registration Messages - SNMP:T,
RADIUS:T/P, Diameter:T, COPS:T
3.5.2 Firewall Friendly - SNMP:F, RADIUS:T, Diameter:P, COPS:P
There was considerable discussion about what it means to be "firewall
friendly". It was suggested that not making the firewall look into
packets much beyond the application port number. Protocols such as
SNMP and COPS are at a disadvantage, as you must look far into the
packet to understand the intended operation. Diameter will have the
disadvantage of SCTP, which is not well deployed or recognized at the
moment.
SNMP and COPS also have the problem that they are used for other
types of operations than just AAA.
Should firewalls have AAA Proxy engines?
We didn't look at "NAT friendly" issues either.
COPS:T
The group is not clear on how this requirement impacts the actual
protocol. Raj explained it to us, but we mostly took it on faith.
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SNMP is generally not acceptable as a general AAA protocol. There
may be some utility in its use for accounting, but the amount of
engineering to turn it into a viable A&A protocol argues against
further consideration.
Radius++ is not considered acceptable as an AAA protocol. There is a
fairly substantial amount of engineering required to make it meet all
requirements, and that engineering would most likely result in
something close to the functionality of Diameter.
Diameter is considered acceptable as an AAA protocol. There is some
minor engineering required to bring it into complete compliance with
the requirements but well within short term capabilities. Diameter
might also benefit from the inclusion of a broader data model ala
COPS.
COPS is considered acceptable as an AAA protocol. There is some
minor to medium engineering required to bring it into complete
compliance with the requirements.
The panel expresses a slight preference for Diameter based on the
perception that the work for Diameter is further along than for COPS.
However, using SCTP as the transport mechanism for Diameter places
SCTP on the critical path for Diameter. This may ultimately result
in COPS being a faster approach if SCTP is delayed in any way.
AAA protocols enforce the security of access to the Internet. The
design of these protocols and this evaluation process took many
security requirements as critical issues for evaluation. A candidate
protocol must meet the security requirements as documented, and must
be engineered and reviewed properly as developed and deployed.
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[AAAReqts] Aboba, B., Clahoun, P., Glass, S., Hiller, T., McCann, P.,
Shiino, H., Walsh, P., Zorn, G., Dommety, G., Perkins, C.,
Patil, B., Mitton, D., Manning, S., Beadles, M., Chen, X.,
Sivalingham, S., Hameed, A., Munson, M., Jacobs, S., Lim,
B., Hirschman, B., Hsu, R., Koo, H., Lipford, M.,
Campbell, E., Xu, Y., Baba, S. and E. Jaques, "Criteria
for Evaluating AAA Protocols for Network Access", RFC
2989, April 2000.
[AAAComp] Ekstein, TJoens, Sales and Paridaens, "AAA Protocols:
Comparison between RADIUS, Diameter and COPS", Work in
Progress.
[SNMPComp] Natale, "Comparison of SNMPv3 Against AAA Network Access
Requirements", Work in Progress.
[RADComp] TJoens and DeVries, "Comparison of RADIUS Against AAA
Network Access Requirements", Work in Progress.
[RADExt] TJoens, Ekstein and DeVries, "Framework for the extension
of the RADIUS (v2) protocol", Work in Progress,
[DIAComp] Calhoun, "Comparison of Diameter Against AAA Network
Access Requirements", Work in Progress.
[COPSComp] Khosravi, Durham and Walker, "Comparison of COPS Against
the AAA NA Requirements", Work in Progress.
[COPSAAA] Durham, Khosravi, Weiss and Filename, "COPS Usage for
AAA", Work in Progress.
David Mitton
Nortel Networks
880 Technology Park Drive
Billerica, MA 01821
Phone: 978-288-4570
EMail: dmitton@nortelnetworks.com
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RFC 3127 AAA Protocol Evaluation Process June 2001
Michael StJohns
Rainmaker Technologies
19050 Pruneridge Ave, Suite 150
Cupertino, CA 95014
Phone: 408-861-9550 x5735
EMail: stjohns@rainmakertechnologies.com
Stuart Barkley
UUNET
F1-1-612
22001 Loudoun County Parkway
Ashburn, VA 20147 US
Phone: 703-886-5645
EMail: stuartb@uu.net
David B. Nelson
Enterasys Networks, Inc. (a Cabletron Systems company)
50 Minuteman Road
Andover, MA 01810-1008
Phone: 978-684-1330
EMail: dnelson@enterasys.com
Basavaraj Patil
Nokia
6000 Connection Dr.
Irving, TX 75039
Phone: +1 972-894-6709
EMail: Basavaraj.Patil@nokia.com
Mark Stevens
Ellacoya Networks
7 Henry Clay Drive
Merrimack, NH 03054
Phone: 603-577-5544 ext. 325
EMail: mstevens@ellacoya.com
Barney Wolff, Pres.
Databus Inc.
15 Victor Drive
Irvington, NY 10533-1919 USA
Phone: 914-591-5677
EMail: barney@databus.com
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Appendix A - Summary Evaluations Consensus Results by Requirement
and Protocol
Requirement Section SNMP Radius++ Diameter COPS
1.1.1 P P T T
1.1.2 P P P T/P
1.1.3 T T/P T T
1.1.4 T P T T
1.1.5 P P T T
1.1.6 F P T T
1.1.7 T T T T
1.1.8 P P T T
1.1.9 T T T T
1.1.10 P T T T
1.1.11 F P T P
1.1.12 F F T P
1.1.13 P/T T T T
1.1.14 T T T T
1.2.1 T T T T
1.2.2 T T T T
1.2.3 T T T T
1.2.4 T T T T
1.2.5 T P P T
1.2.6 P T/P T T
1.3.1 P/F T T T
1.3.2 P T T/P P
1.3.3 T/P/F T T P
1.3.4 F T T T
1.3.5 P/F P T/P T
1.3.6 P P P T/P
1.3.7 F P/F P T/P
1.3.8 T P T T
1.4.1 T T T T
1.4.2 T T T T
1.4.3 T T T T
1.4.4 T F P P
1.4.5 T T T T
1.4.6 T T T T
1.4.7 T T T T
1.5.1 T T/P T T
1.5.2 F T P P
1.5.3 F P T T
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Appendix B - Review of the Requirements
Comments from the Panel on then work in progress, "Criteria for
Evaluating AAA Protocols for Network Access" now revised and
published as RFC 2989. This became the group standard interpretation
of the requirements at the time.
Scalability - In clarification [a], delete "and tens of thousands of
simultaneous requests." This does not appear to be supported by any
of the three base documents.
Transmission level security - [Table] Delete the ROAMOPS "M" and
footnote "6". This appears to be an over generalization of the
roaming protocol requirement not necessarily applicable to AAA.
Data object confidentiality - [Table] Delete the MOBILE IP "S" and
footnote "33". The base document text does not appear to support
this requirement.
Reliable AAA transport mechanism - In clarification [h] delete
everything after the "...packet loss" and replace with a ".". The
requirements listed here are not necessarily supported by the base
document and could be mistakenly taken as requirements for the AAA
protocol in their entirety.
Run over IPv4 - [Table] Replace the MOBILE IP footnote "17" with
footnote "33". This appears to be a incorrect reference.
Run over IPv6 - [Table] Replace the MOBILE IP footnote "18" with a
footnote pointing to section 8 of [8]. This appears to be an
incorrect reference.
Auditability - Clarification [j] does not appear to coincide with the
NASREQ meaning of Auditability. Given that NASREQ is the only
protocol with an auditability requirement, this section should be
aligned with that meaning.
Shared secret not required - [Table] General - This section is
misleadingly labeled. Our team has chosen to interpret it as
specified in clarification [k] rather than any of the possible
interpretations of "shared secret not required". We recommend the
tag in the table be replaced with "Dual App and Transport Security
Not Required" or something at least somewhat descriptive of [k].
Delete the NASREQ "S" and footnote "28" as not supported by the
NASREQ document. Delete the MOBILE IP "O" and footnotes "34" and 39"
as not supported.
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NAI Support - [Table] Replace MOBILE IP footnote "38" with "39".
This appears to be a more appropriate reference.
CHAP Support - [Table] Delete MOBILE IP "O" as unsupported.
EAP Support - [Table] Delete MOBILE IP "O" as unsupported.
PAP/Clear-Text Support - [Table] Replace NASREQ footnote "10" with
"26" as being more appropriate. Replace ROAMOPS "B" with "O". The
reference text appears to not explicitly ban this and specifically
references clear text for OTP applications. Delete MOBILE IP "O" as
unsupported.
Re-authentication on demand - Clarification [e] appears to go beyond
the requirements in NASREQ and MOBILE IP. [Table] Delete MOBILE IP
footnote "30" as inapplicable.
Authorization Only without Authentication - Clarification [f] does
not include all NASREQ requirements, specifically that unneeded
credentials MUST NOT be required to be filled in. Given that there
are no other base requirements (after deleting the MOBILE IP
requirement) we recommend that clarification [f] be brought in line
with NASREQ. [Table] Delete MOBILE IP "O" and footnote "30". The
referenced text does not appear to support the requirement.
Static and Dynamic... - Clarification [a] appears to use a
particularly strange definition of static and dynamic addressing.
Recommend clarification here identifying who (e.g. client or server)
thinks address is static/dynamic. [Table] ROAMOPS "M" appears to be
a derived requirement instead of directly called out. The footnote
"1" should be changed to "5" as being more appropriate. A text
clarification should be added to this document identifying the
derived requirement.
RADIUS Gateway capability - [Table] Delete the MOBILE IP "O" and
footnote "30". The referenced text does not appear to support the
requirement.
Reject capability - [Table] Delete the NASREQ "M" and footnote "12".
The NASREQ document does not appear to require this capability.
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Reauthorization on Demand - [Table] Delete the MOBILE IP "S" and
footnotes "30,33" The referenced text does not support this
requirement.
Support for Access Rules... - Clarification [e] has a overbroad list
of requirements. NASREQ only requires 5-8 on the list, and as The
MOBILE IP requirement is not supported by its references, this
clarification should match NASREQ requirements. [Table] Delete the
MOBILE IP "O" and footnotes "30,37" as not supported.
State Reconciliation - Clarification [f] should be brought in line
with NASREQ requirements. The clarification imposes overbroad
requirements not required by NASREQ and NASREQ is the only service
with requirements in this area.
Real-Time accounting - [Table] Replace MOBILE IP footnote [39] with a
footnote pointing to section 3.1 of [3] as being more appropriate.
Mandatory Compact Encoding - [Table] Delete MOBILE IP "M" and
footnote "33" as the reference does not support the requirement.
Accounting Record Extensibility - [Table] Delete NASREQ "M" and
footnote "15" as the reference does not support the requirement.
Accounting Time Stamps - [Table] Delete MOBILE IP "S" and footnote
"30" as they don't support the requirement. Replace MOBILE IP
footnote "40" with a footnote pointing to section 3.1 of [3] as being
more appropriate.
Dynamic Accounting - [Table] Replace the NASREQ footnote "18" with a
footnote pointing to section 8.4.1.5 of [3]. Delete the MOBILE IP
"S" and footnote "30" as the reference does not support the
requirement.
Footnote section.
[40] should be pointing to 6.1 of [4].
[41] should be pointing to 6.2.2 of [4].
[45] should be pointing to 6.4 of [4].
[46] should be pointing to 8 of [4].
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Appendix C - Position Briefs
Evaluation of SNMP AAA Requirements
PRO Evaluation
Evaluator - Stuart Barkley
Ref [1] is "Comparison of SNMPv3 Against AAA Network Access
Requirements", aka 'the document'
Ref [2] is the aaa eval criteria as modified by us, aka 'the
requirements'
The document uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance. For each section
I've indicated my grade for the section. If there is a change, I've
indicated that and the grade given by the authors.
1 Per item discussion
1.1 General Requirements
1.1.1 Scalability - Grade T
The document indicates that SNMP can adequately handle that scale
from the requirements document. Since most current uses are ppp
connections and SNMP is already capable of handling the interface
table and other per session tables it is clear that basic capacity
exists. Additions to support other tables and variables scales in a
simple linear fashion with the number of additional variables and
protocol interactions. Regardless of the final selected protocol
handling the scaling required is not a trivial undertaking. SNMP can
draw upon existing network management practices to assist in this
implementation.
1.1.2 Fail-over - Grade T
SNMP is of vital importance to the operation of most networks.
Existing infrastructures can handle required failover or other
redundant operations.
1.1.3 Mutual Authentication - Grade T
The use of shared secrets described in the document is a well
understood method of integrity control. Although shared secrets
don't necessarily provide full authentication since other parties may
also have the same secrets, the level of authentication is sufficient
for the task at hand. In many cases the SNMP infrastructure will
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already exist and shared secrets should already be properly managed
on an operational network. A failure of the SNMP shared secret
approach regardless of the AAA protocol will likely leave equipment
and systems open to substantial misuse bypassing any more elaborate
AAA authentication.
1.1.4 Transmission Level Security - Grade T
SNMPv3 provides many additional security options which were not
available or were more controversial in previous SNMP versions.
1.1.5 Data Object Confidentiality - New Grade P (from T)
The document discusses SNMPv3 which can provide data confidentially
for data passing over the wire. There is substantial implied AAA
architecture (brokers and proxies) in the requirements that full
conformance is difficult to determine. In particular, the evaluator
has difficulty with the concept of "the target AAA entity for whom
the data is ultimately destined", but will concede that the desired
requirement is only partially met (most especially with the transfer
of a PAP password).
1.1.6 Data Object Integrity - New Grade T (from P)
SNMP has full capabilities that allow the authentication of the data.
Brokers, proxies or other intermediaries in the data chain can verify
the source of the information and determine that the data has not
been tampered with. The document downgrades the grade to P because
of confusion over the integrity checking role of intermediaries.
1.1.7 Certificate Transport - Grade T
The requirements require the capability of transporting certificates
but do not have any specific use for the certificates. The
requirements make assumptions that the protocol selected will be
dependent upon certificates, but this is not necessarily true. SNMP
can transport arbitrary objects and can transport certificates if
necessary. The document indicates some issues with size of
certificates and current maximum practical data sizes, however if the
compact encoding requirement extends to the internal certificate
information this should be less of an issue.
1.1.8 Reliable AAA Transport - New Grade T (from P)
The requirements is stated rather strongly and makes substantial
assumptions of AAA protocol architecture and based upon current
protocols and their failings. SNMP allows for great flexibility in
retransmission schemes depending upon the importance of the data.
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1.1.9 Run over IPv4 - Grade T
SNMP has operated in this mode for many years.
1.1.10 Run over IPv6 - New Grade T (from P)
SNMP must support IPv6 for many other systems so support for this
should be possible by the time the requirement becomes effective.
The document indicates that experimental versions satisfying this
requirement are already in existence.
1.1.11 Support Proxy and Routing Brokers - New Grade T (from P)
The requirements make significant assumptions about the final
architecture. It is well within the capabilities of SNMP to provide
intermediaries which channel data flows between multiple parties.
The document downgrades SNMPs compliance with this requirement due to
issues which are covered more specifically under "Data Object
Confidentially" which the evaluator has downgraded to P.
1.1.12 Auditability - New Grade T (from F)
Data flows inside SNMP are easily auditable by having secondary data
flows established which provide copies of all information to
auxiliary servers. The document grades this as a failure, but this
support is only minor additions within a more fully fleshed out set
of data flows.
1.1.13 Shared Secret Not Required - Grade T
Shared secrets are not required by SNMP. They are desirable in many
instances where a lower level does not provide the necessary
capabilities. The document supplies pointers to various security
modes available.
1.1.14 Ability to Carry Service Specific Attributes - Grade T
SNMP has long had the ability for other parties to create new
unambiguous attributes.
1.2 Authentication Requirements
1.2.1 NAI Support - Grade T
SNMP easily supports this. NAIs were defined to be easily carried in
existing protocols.
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1.2.2 CHAP Support - Grade T
SNMP can easily provide objects to pass the necessary information for
CHAP operation.
1.2.3 EAP Support - New Grade T (from P)
SNMP can easily provide objects to pass the necessary information for
EAP operation. As with CHAP or PAP MIB objects can be created to
control this operation thus the upgrade from the document grade.
1.2.4 PAP/Clear-text Passwords - New Grade P (from T)
SNMP can easily provide objects to pass the necessary information for
PAP operation. The requirement about non-disclosure of clear text
passwords make assumptions about the protocol implementation. The
choice to use clear text passwords is inherently insecure and forced
protocol architecture don't really cover this. This requirement
grade is downgraded to P (partial) because the document does not
really address the confidentially of the data at application proxies.
1.2.5 Reauthorization on demand - Grade T
SNMP can easily provide objects to control this operation.
1.2.6 Authorization w/o Authentication - New Grade T (from T)
The document makes an incorrect interpretation of this requirement.
However, SNMP makes no restriction which prevents to desired
requirements. No actual change of grade is necessary, since both the
actual requirements and the incorrect interpretation are satisfied by
SNMP.
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - Grade T
SNMP can easily provide objects to control this operation.
1.3.2 RADIUS Gateway Capability - Grade T
As the document describes, with the addition of any necessary
compatibility variables SNMP can be gatewayed to RADIUS applications.
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1.3.3 Reject Capability - Grade T
Any of the active components in the SNMP based structure could decide
to reject and authentication request for any reason. Due to mixing
different levels of requirements the document doesn't attempt to
directly address this, instead indicating that a higher level
application can cause this operation.
1.3.4 Preclude Layer 2 Tunneling - New Grade T (from ?)
Nothing in SNMP explicitly interacts with the selection of any
tunneling mechanisms the client may select. The document author was
unclear about the needs here.
1.3.5 Reauth on Demand - Grade T
SNMP can easily provide objects to control this operation.
1.3.6 Support for ACLs - Grade T
The document indicates that should it be desired SNMP can provide
objects to control these operations. In addition, active components
can apply substantial further configurable access controls.
1.3.7 State Reconciliation - Grade T
The requirements describe an over broad set of required capabilities.
The document indicates concern over incompatibilities in the
requirements, however SNMP can provide methods to allow active
components to reacquire lost state information. These capabilities
directly interact with scalability concerns and care needs to be
taken when expecting this requirement to be met at the same time as
the scalability requirements.
1.3.8 Unsolicited Disconnect - Grade T
The document indicates that SNMP can easily provide objects to
control this operation.
1.4 Accounting Requirements
1.4.1 Real Time Accounting - Grade T
SNMP can provide this mode of operation. The document outlines
methods both fully within SNMP and using SNMP to interface with other
transfer methods. Many providers already use SNMP for real time
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notification of other network events. This capability can directly
interact with scalability concerns and implementation care needs to
be taken to make this properly interact is large scale environments.
1.4.2 Mandatory Compact Encoding - Grade T
The document indicates the possibility of controlling external
protocols to handle data transmissions where the BER encoding of SNMP
objects would be considered excessive. SNMP BER encoded protocol
elements are generally in a fairly compact encoding form compared
with text based forms (as used in some existing radius log file
implementations). This interacts with the general requirement for
carrying service specific attributes and the accounting requirement
for extensibility. With careful MIB design and future work on SNMP
payload compression the SNMP coding overhead can be comparable with
other less extensible protocols.
1.4.3 Accounting Record Extensibility - Grade T
SNMP has a strong tradition of allowing vendor specific data objects
to be transferred.
1.4.4 Batch Accounting - Grade T
There are many methods which a SNMP based system could use for batch
accounting. The document discusses SNMP parameters to control the
batching process and indicates that certain existing MIBs contain
examples of implementation strategies. SNMP log tables can provide
accounting information which can be obtained in many methods not
directly related to real time capabilities. The underlying system
buffering requirements are similar regardless of the protocol used to
transport the information.
1.4.5 Guaranteed Delivery - Grade T
SNMP is very amenable to providing guaranteed delivery. Particularly
in a pull model (versus the often assumed push model) the data
gatherer can absolutely know that all data has been transfered. In
the common push model the data receiver does not know if the
originator of the data is having problems delivering the data.
1.4.6 Accounting Timestamps - Grade T
Timestamps are used for many SNMP based operations. The document
points at the DateAndTime textual convention which is available for
use. As with all environments the timestamps accuracy needs
evaluation before the information should be relied upon.
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1.4.7 Dynamic Accounting - Grade T
As long as there is some way to relate multiple records together
there are no problems resolving multiple records for the same
session. This interacts with the scalability requirement and care
must be taken when implementing a system with both of these
requirements.
1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - Grade T
SNMP can easily provide objects to transfer this information.
1.5.2 Firewall Friendly - New Grade T (from P)
SNMP is already deployed in many operational networks. SNMPv3
addresses most concerns people had with the operation of previous
versions. True SNMPv3 proxies (as opposed to AAA proxies) should
become commonplace components in firewalls for those organizations
which require firewalls.
1.5.3 Allocation of Local Home Agent - New Grade T (from ?)
SNMP is not concerned with the LHA. This can be under control of the
Local network to meet its needs.
2. Summary Discussion
SNMP appears to meet most stated requirements. The areas where the
SNMP proposal falls short are areas where specific AAA architectures
are envisioned and requirements based upon that architecture are
specified.
Scaling of the protocol family is vital to success of a AAA suite.
The SNMP protocol has proved scalable in existing network management
and other high volume data transfer operations. Care needs to be
taken in the design of a large scale system to ensure meeting the
desired level of service, but this is true of any large scale
project.
3. General Requirements
SNMP is well understood and already supported in many ISP and other
operational environments. Trust models already exist in many cases
and can be adapted to provide the necessary access controls needed by
the AAA protocols. Important issues with previous versions of SNMP
have been corrected in the current SNMPv3 specification.
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The SNMP proposal is silent on the specific data variables and
message types to be implemented. This is largely due to the
requirements not specifying the necessary data elements and the time
constraints in extracting that information from the base document
set. Such a data model is necessary regardless of the ultimate
protocol selected.
4. Summary Recommendation
SNMP appears to fully meet all necessary requirements for the full
AAA protocol family.
Evaluation of SNMP AAA Requirements
CON Evaluation
Evaluator - Michael StJohns
Ref [1] is "Comparison of SNMPv3 Against AAA Network Access
Requirements", aka 'the document'
Ref [2] is the aaa eval criteria as modified by us.
The document uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance. For each section
I've indicated my grade for the section. If there is no change, I've
indicated that and the grade given by the authors.
Section 1 - Per item discussion
1.1 General Requirements
1.1.1 Scalability - Although the document indicates compliance with
the requirement, its unclear how SNMP actually meets those
requirements. The document neither discusses how SNMP will scale,
nor provides applicable references. The argument that there is an
existence proof given the deployed SNMP systems appears to assume
that one manager contacting many agents maps to many agents (running
AAA) contacting one AAA server. A server driven system has
substantially different scaling properties than a client driven
system and SNMP is most definitely a server (manager) driven system.
Eval - F
1.1.2 Fail-over - The document indicates the use of application level
time outs to provide this mechanism, rather than the mechanism being
a characteristic of the proposed protocol. The protocol provides
only partial compliance with the requirement. Eval - P
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1.1.3 Mutual Authentication - There is some slight handwaving here,
but the protocol's USM mode should be able to support this
requirement. Eval - No Change (T)
1.1.4 Transmission Level Security - The authors should elaborate on
the specific use of the SNMPv3 modes to support these requirements,
but the text is minimally acceptable. Eval - No Change (T)
1.1.5 Data Object Confidentiality - The authors describe a mechanism
which does not appear to completely meet the requirement. VACM is a
mechanism for an end system (agent) to control access to its data
based on manager characteristics. This mechanism does not appear to
map well to this requirement. Eval - P
1.1.6 Data Object Integrity - There appears to be some handwaving
going on here. Again, SNMP does not appear to be a good match to
this requirement due to at least in part a lack of a proxy
intermediary concept within SNMP. Eval - F
1.1.7 Certificate Transport - The document does indicate compliance,
but notes that optimization might argue for use of specialized
protocols. Eval - No Change (T)
1.1.8 Reliable AAA Transport - The document indicates some confusion
with the exact extent of this requirement. Given the modifications
suggested by the eval group to the explanatory text in [2] for the
related annotation, the point by point explanatory text is not
required. The document does indicate that the use of SNMP is
irrespective of the underlying transport and the support of this
requirement is related at least partially to the choice of transport.
However, SNMP over UDP - the most common mode for SNMP - does not
meet this requirement. Eval - No Change (P)
1.1.9 Run over IPv4 - While the evaluator agrees that SNMPv3 runs
over V4, the authors need to point to some sort of reference. Eval -
No Change (T)
1.1.10 Run over IPv6 - The document indicates both experimental
implementations and future standardization of SNMPv3 over IPv6. Eval
- No Change (P)
1.1.11 Support Proxy and Routing Brokers - The section of the
document (5.5.3) that, by title, should have the discussion of SNMP
proxy is marked as TBD. The section notes that the inability to
completely comply with the data object confidentiality and integrity
requirements might affect the compliance of this section and the
evaluator agrees. Eval - F
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1.1.12 Auditability - The document indicates no compliance with this
requirement. Eval - No Change (F)
1.1.13 Shared Secret Not Required - Slight handwaving here, but
SNMPv3 does not necessarily require use of its security services if
other security services are available. However, the interaction with
VACM in the absence of USM is not fully described and may not have
good characteristics related to this requirement. Eval - P
1.1.14 Ability to Carry Service Specific Attributes - SNMP complies
via the use of MIBs. Eval - No Change (T)
1.2 Authentication Requirements
1.2.1 NAI Support - The document indicates that MIB objects can be
created to meet this requirement, but gives no further information.
Eval - P
1.2.2 CHAP Support - The document indicates that MIB objects can be
created to meet this requirement, but gives no further information.
Given the normal CHAP model, its unclear exactly how this would work.
Eval - F
1.2.3 EAP Support - The document notes that EAP payloads can be
carried as specific MIB objects, but also notes that further design
work would be needed to fully incorporate EAP. Eval - No Change (P)
1.2.4 PAP/Clear-text Passwords - The document notes the use of MIB
objects to carry the clear text passwords and the protection of those
objects under normal SNMPv3 security mechanisms. Eval - No Change
(T)
1.2.5 Reauthorization on demand - While there's some handwaving here,
its clear that the specific applications can generate the signals to
trigger reauthorization under SNMP. Eval - No Change (T)
1.2.6 Authorization w/o Authentication - The author appears to be
confusing the AAA protocol authorization with the AAA user
authorization and seems to be over generalizing the ability of SNMP
to deal with general AAA user authorization. Eval - F
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - The reference to MIB
objects without more definite references or descriptions continues to
be a negative. While the evaluator agrees that MIB objects can
represent addresses, the document needs to at least lead the reader
in the proper direction. Eval - F
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1.3.2 RADIUS Gateway Capability - The transport and manipulation of
Radius objects appears to be only a part of what is required. Eval -
P
1.3.3 Reject Capability - Again, a clarification of how SNMP might
accomplish this requirement would be helpful. The overall document
lacks a theory of operation for SNMP in an AAA role that might have
clarified the various approaches. Eval - F
1.3.4 Preclude Layer 2 Tunneling - Document indicates lack of
understanding of this requirement. Eval - F
1.3.5 Reauth on Demand - See response in 1.3.3 above. None of the
text responding to this requirement, nor any other text in the
document, nor any of the references describes the appropriate
framework and theory. Eval - F
1.3.6 Support for ACLs - The response text again references MIB
objects that can be defined to do this job. There is additional
engineering and design needed before this is a done deal. Eval - P
1.3.7 State Reconciliation - The text fails to address the basic
question of how to get the various parts of the AAA system back in
sync. Eval - F
1.3.8 Unsolicited Disconnect - Assuming that the NAS is an SNMP agent
for an AAA server acting as an SNMP manager the evaluator concurs.
Eval - No Change (T).
1.4 Accounting Requirements
1.4.1 Real Time Accounting - SNMP Informs could accomplish the
requirements. Eval - No Change (T)
1.4.2 Mandatory Compact Encoding - This is a good and reasonable
response. SNMP can vary the style and type of reported objects to
meet specific needs. Eval - No Change (T).
1.4.3 Accounting Record Extensibility - MIBs are extensible. Eval -
No Change (T)
1.4.4 Batch Accounting - MIBs provide data collection at various
times. Eval - No Change (T)
1.4.5 Guaranteed Delivery - There's some weasel wording here with
respect to what guaranteed means, but the description of mechanisms
does appear to meet the requirements. Eval - No Change (T)
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1.4.6 Accounting Timestamps - Accounting records can use the
DateAndTime Textual Convention to mark their times. Eval - No Change
(T)
1.4.7 Dynamic Accounting - The author may have partially missed the
point on this requirement. While the number of records per session
is not of great interest, the delivery may be. The author should go
a little more into depth on this requirement. Eval - No Change (T)
1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - Registration
messages can probably be encoded as SNMP messages. Eval - No Change
(T)
1.5.2 Firewall Friendly - There's a chicken and egg problem with the
response to the requirement in that the author hopes that SNMP as an
AAA protocol will encourage Firewall vendors to make SNMP a firewall
friendly protocol. Eval - F
1.5.3 Allocation of Local Home Agent - The author disclaims an
understanding of this requirement. Eval - F
2. Summary Discussion
The documents evaluation score was substantially affected by a lack
of any document, reference or text which described a theory of
operation for SNMP in AAA mode. Of substantial concern are the items
relating to the AAA server to server modes and AAA client to server
modes and the lack of a map to the SNMP protocol for those modes.
The evaluator also notes that the scaling issues of SNMP in SNMP
agent/manager mode are in no way indicative of SNMP in AAA
client/server mode. This has a possibility to substantially impair
SNMPs use in an AAA role.
However, SNMP may have a reasonable role in the Accounting space.
SNMP appears to map well with existing technology, and with the
requirements.
3. General Requirements
SNMP appears to meet the general requirements of an IP capable
protocol, but may not have a proper field of use for all specific
requirements.
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4. Summary Recommendation
Recommended in Part. SNMP is NOT RECOMMENDED for use as either an
authentication or authorization protocol, but IS RECOMMENDED for use
as an accounting protocol.
Evaluation of RADIUS AAA Requirements PRO Evaluation
Evaluator - Mark Stevens
Ref [1] is "Comparison of RADIUS Against AAA Network Access
Requirements"
Ref [2] is "Framework for the extension of the RADIUS(v2) protocol"
Ref [3] is the aaa eval criteria as modified by us.
The documents uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance.
For each section I've indicated my grade for the section. I have
indicated whether or not my evaluation differs from the statements
made with respect to RADIUS++. The evaluation ratings as given below
may differ from the evaluations codified in the document referred to
as, "Comparison of RADIUS Against AAA Network Access Requirements"
without any indication.
1.1 General Requirements
1.1.1 [a] Scalability - In as much as a protocol's scalability can be
measured, the protocol seems to transmit information in a fairly
efficient manner.So, in that the protocol appears not to consume an
inordinate amount of bandwidth relative to the data it is
transmitting, this protocol could be considered scalable. However,
the protocol has a limit in the number of concurrent sessions it can
support between endpoints. Work arounds exist and are in use. Eval
- P (no change)
1.1.2 [b] Fail-over - The document indicates the use of application
level time outs to provide this mechanism, rather than the mechanism
being a characteristic of the proposed protocol. The fail-over
requirement indicates that the protocol must provide the mechanism
rather than the application. The implication is that the application
need not be aware that the fail-over and subsequent correction when
it happens. The application using the RADIUS++ protocol will be
involved in fail-over recovery activities. The protocol layer of the
software does not appear to have the capability built-in. Given the
wording of the requirement: Eval - P (changed from T)
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1.1.3 [c] Mutual Authentication - The RADIUS++ protocol provides
shared-secret as a built-in facility for mutual authentication. The
authors of the document suggest the use of IPSec to obtain mutual
authentication functions. The RADIUS++ protocol provides no road
blocks to obtaining mutual authentication between instances of AAA
applications, however the protocol provides no facilities for doing
so.
1.1.4 [d] Transmission Level Security - The RADIUS++ protocol
provides no transmission level security features, nor does it
preclude the use of IPSec to obtain transmission level security.
Eval - P (no change)
1.1.5 [e] Data Object Confidentiality - The document describes a
RAIDUS++ message designed to server as an envelope in which encrypted
RADIUS messages (attributes) may be enclosed. Eval - T (no change)
1.1.6 [f] Data Object Integrity - Using visible signatures, the
RADIUS++ protocol appears to meet this requirement. Eval - T (no
change)
1.1.7 [g] Certificate Transport - The document indicates compliance
through the use of the CMS-Data Radius Attribute (message). Eval - T
(no change)
1.1.8 [h] Reliable AAA Transport - The document points out that
RADIUS++ can be considered a reliable transport when augmented with
Layer 2 Tunneling Protocol. The protocol itself does not provide
reliability features. Reliability remains the responsibility of the
application or a augmenting protocol. Eval - P (no change)
1.1.9 [i] Run over IPv4 - Eval - T (no change)
1.1.10 [j] Run over IPv6 - an IPv6 Address data type must be defined.
Eval - T (no change)
1.1.11 [k] Support Proxy and Routing Brokers - There is no mechanism
for rerouting requests, but an extension can be made to do so. Eval
- T (no change)
1.1.12 [l] Auditability - The document indicates no compliance with
this requirement. Eval - F (no change)
1.1.13 [m] Shared Secret Not Required - RADIUS++ can be configured to
run with empty shared secret values. Eval - T (no change)
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1.1.14 [n] Ability to Carry Service Specific Attributes - Vendor
escape mechanism can be used for this purpose.. Eval - T (no
change)
1.2 Authentication Requirements
1.2.1 [a] NAI Support - Eval - T (no change)
1.2.2 [b] CHAP Support - Subject to dictionary attacks. Eval - P
(changed from T)
1.2.3 [c] EAP Support - Eval - T (no change)
1.2.4 [d] PAP/Clear-text Passwords - No end-to-end security, but
potential for encapsulation exists within current paradigm of the
protocol. - Eval -T (no change)
1.2.5 [e] Reauthentication on demand - The RADIUS protocol
supports re-authentication. In case re-authentication is initiated
by the user or AAA client, the AAA client can send a new
authentication request. Re-authentication can be initiated from the
visited or home AAA server by sending a challenge message to the AAA
client. Eval - T (no change)
1.2.6 [f] Authorization w/o Authentication - A new message type can
be created to enable RADIUS++ to support Aw/oA . Eval - T (no
change)
1.3 Authorization Requirements
1.3.1[a] Static and Dynamic IP Addr Assignment - Both supported.
IPv6 would require the definition of a new address data type. Eval -
P (no change)
1.3.2 [b] RADIUS Gateway Capability - The transport and manipulation
of RADIUS objects appears to be only a part of what is required.
Requirement seems to be worded to preclude RADIUS. Eval - P (changed
from T)
1.3.3 [c] Reject Capability - Eval -T
1.3.4 [d] Preclude Layer 2 Tunneling - I do not see a definition in
the AAA eval criteria document. Eval - ?
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1.3.5 [e] Reauthorization on Demand - Implementation in the field
demonstrate that extensions to RADIUS can support the desired
behavior. Re-authentication is currently coupled to re-
authorization. Eval - P (no change)
1.3.6 [f] Support for ACLs - Currently done in the applications
behind the RADIUS end points, not the within the protocol. RADIUS++
could define additional message types to deal with expanded access
control within new service areas. Eval - P (no change)
1.3.7 [g] State Reconciliation - Eval - F (no change)
1.3.8 [h] Unsolicited Disconnect - RADIUS++ extensions to support.
Eval - T. (no change)
1.4 Accounting Requirements
1.4.1 [a] Real Time Accounting - Eval - T (no change)
1.4.2 [b] Mandatory Compact Encoding - Eval - T (no change)
1.4.3 [c] Accounting Record Extensibility - Eval - T (no change)
1.4.4 [d] Batch Accounting - RADIUS++ offers no new features to
support batch accounting. Eval - F No change)
1.4.5 [e] Guaranteed Delivery - Retransmission algorithm employed.
Eval - T (no change)
1.4.6 [f] Accounting Timestamps - RADIUS++ extensions support
timestamps. Eval - T (no change)
1.4.7 [g] Dynamic Accounting - RADIUS++ extensions to support. Eval
- T (no change)
1.5 MOBILE IP Requirements
1.5.1 [a] Encoding of MOBILE IP Registration Messages - RADIUS++
extensions can be made to include registration messages as an opaque
payload. Eval - T (no change)
1.5.2 [b] Firewall Friendly - RADIUS is known to be operational
in environments where firewalls acting as a proxy are active. Eval -
T (no change)
1.5.3 [c] Allocation of Local Home Agent -Requirement statement needs
some clarification and refinement. Eval - F (no change)
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2. Summary Discussion
The RADIUS protocol, and its associated extensions, is presently not
fully compliant with the AAA Network Access requirements.
However, it is possible with a small effort to extend present
procedures to meet the requirements as listed in, while maintaining a
high level of interoperability with the wide deployment and
installed base of RADIUS clients and servers.
3. General Requirements
RADIUS++ the protocol and the application meet the majority of the
requirements and can be extended to meet the requirements where
necessary.
4. Summary Recommendation
RADIUS++ as it could be developed would provide a level of backward
compatibility that other protocols cannot achieve. By extending
RADIUS in the simple ways described in the documents listed above,
the transition from existing RADIUS-based installations to RADIUS++
installations would be easier. Although accounting continues to be
weaker than other approaches, the protocol remains a strong contender
for continued use in the areas of Authorization and Authentication.
Evaluation of RADIUS++ (sic) AAA Requirements CON Evaluation
Evaluator - David Nelson
Ref [1] is "Comparison of RADIUS Against AAA Network Access
Requirements", a.k.a. 'the document'
Ref [2] is "Framework for the extension of the RADIUS(v2) protocol",
a.k.a. 'the protocol'
Ref [3] is the AAA evaluation criteria as modified by us.
Ref [4] is RFC 2869.
Ref [5] is an expired work in progress "RADIUS X.509 Certificate
Extensions".
Ref [6] is RFC 2868
The document uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance. Evaluator's
Note: The document [1] pre-dates the protocol [2]. It is clear from
reading [2], that some of the issues identified as short comings in
[1] are now addressed in [2]. The evaluator has attempted to take
note of these exceptions, where they occur.
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Section 1 - Per item discussion
1.1 General Requirements
1.1.1 Scalability - The document [1] indicates partial compliance,
largely in deference to the "tens of thousands of simultaneous
requests" language in [3], that has been deprecated. The issue of
simultaneous requests from a single AAA client is addressed in [1],
indicating that the apparent limitation of 256 uniquely identifiable
outstanding request can be worked around using well known techniques,
such as the source UDP port number of the request. The document
claims "P", and the evaluator concurs.
1.1.2 Fail-over - The document [1] indicates the use of application
level time outs to provide the fail-over mechanism. Since the AAA
protocol is indeed an application-layer protocol, this seems
appropriate. There are significant issues of how to handle fail-
over in a proxy-chain environment that have not been well addressed,
however. The document claims "T", and the evaluator awards "P".
1.1.3 Mutual Authentication - The document [1] indicates that mutual
authentication exists in the presence of a User-Password or CHAP-
Password attribute in an Access-Request packet or the Message-
Authenticator [4] in any packet. Once again, this addresses hop-by-
hop authentication of RADIUS "peers", but does not fully address
proxy-chain environments, in which trust models would need to be
established. The document further indicates that strong mutual
authentication could be achieved using the facilities of IPsec. This
claim would apply equally to all potential AAA protocols, and cannot
be fairly said to be a property of the protocol itself. The document
claims "T", and the evaluator awards "F".
1.1.4 Transmission Level Security - The document [1] indicates that
transmission layer security, as defined in [3], is provided in the
protocol, using the mechanisms described in section 1.1.3. It should
be noted that this requirement is now a SHOULD in [3]. The document
claims "P", and the evaluator concurs.
1.1.5 Data Object Confidentiality - The document [1] indicates that
end-to-end confidentiality is not available in RADIUS, but goes on to
say that it could be added. The protocol [2] actually makes an
attempt to specify how this is to be done, in section 4.3.2.2 of [2],
using a CMS-data attribute, based in large part upon RFC 2630. The
evaluator has not, at this time, investigated the applicability of
RFC 2630 to the AAA work. The document claims "F", but in light of
the specifics of the protocol [2], the evaluator awards "P".
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1.1.6 Data Object Integrity - The document [1] indicates that end-
to-end integrity is not available in RADIUS, but goes on to say that
it could be added. The protocol [2] actually makes an attempt to
specify how this is to be done, in section 4.3.2.1 of [2], using a
CMS-data attribute, based in large part upon RFC 2630. The evaluator
has not, at this time, investigated the applicability of RFC 2630 to
the AAA work. The document claims "F", but in light of the specifics
of the protocol [2], the evaluator awards "P".
1.1.7 Certificate Transport - The document [1] indicates that
certificate transport is not available in RADIUS, but goes on to say
that it could be added. The protocol [2] actually makes an attempt
to specify how this is to be done, in section 4.3.2.3 of [2], using a
CMS-data attribute, based in large part upon RFC 2630. The evaluator
has not, at this time, investigated the applicability of RFC 2630 to
the AAA work. Other relevant work in the area of certificate support
in RADIUS may be found in an expired work in progress, "RADIUS X.509
Certificate Extensions" [5]. The document claims "F", but in light
of the specifics of the protocol [2], the evaluator awards "P".
1.1.8 Reliable AAA Transport - The document [1] indicates that RADIUS
provides partial compliance with the requirements of the original AAA
requirements document. However, in [3], the requirement has been
simplified to "resilience against packet loss". Once again, the
evaluator finds that the protocol [2] meets this criteria on a hop-
by-hop basis, but fails to effectively address these issues in a
proxy-chain environment. The document claims "P", and the evaluator
awards "F".
1.1.9 Run over IPv4 - RADIUS is widely deployed over IPv4. The
document claims "T", and the evaluator concurs.
1.1.10 Run over IPv6 - The document [1] indicates that adoption of a
limited number of new RADIUS attributes to support IPv6 is
straightforward. Such discussion has transpired on the RADIUS WG
mailing list, although that WG is in the process of shutting down.
The document claims "P", and the evaluator concurs.
1.1.11 Support Proxy and Routing Brokers - The document [1] indicates
that RADIUS is widely deployed in proxy-chains of RADIUS servers.
This is equivalent to the Proxy Broker case, but the Routing Broker
case is a different requirement. The protocol [2] does not describe
any detail of how a Routing Broker might be accommodated, although it
opens the door by indicating that the RADIUS++ protocol is peer-to-
peer, rather than client/server. The document claims "P", and the
evaluator awards "F".
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1.1.12 Auditability - The document [1] indicates no compliance with
this requirement. The document claims "F", and the evaluator
concurs.
1.1.13 Shared Secret Not Required - The document [1] indicates that
RADIUS may effectively skirt the requirement of application-layer
security by using a value of "zero" for the pre-shared secret. While
this is a bit creative, it does seem to meet the requirement. The
document claims "T" and the evaluator concurs.
1.1.14 Ability to Carry Service Specific Attributes - RADIUS has a
well defined Vendor-Specific Attribute, which, when properly used,
does indeed provide for the ability to transport service-specific
attributes. The document claims "T", and the evaluator concurs.
1.2 Authentication Requirements
1.2.1 NAI Support - The document [1] indicates that RADIUS specifies
the NAI as one of the suggested formats for the User-Name attribute.
The document claims "T", and the evaluator agrees.
1.2.2 CHAP Support - CHAP support is widely deployed in RADIUS. The
document claims [1] "T", and the evaluator concurs.
1.2.3 EAP Support - The document [1] indicates that EAP support in
RADIUS is specified in [4]. The document claims [1] "T", and the
evaluator concurs.
1.2.4 PAP/Clear-text Passwords - The document [1] indicates that
RADIUS provides protection of clear-text passwords on a hop-by-hop
basis. The protocol [2] indicates how additional data
confidentiality may be obtained in section 4.3.2.2 of [2], using a
CMS-data attribute, based in large part upon RFC 2630. The evaluator
has not, at this time, investigated the applicability of RFC 2630 to
the AAA work. The document claims [1] "F", but in light of the
specifics of the protocol [2], the evaluator awards "P".
1.2.5 Reauthentication on demand - The document [1] indicates that
RADIUS may accomplish re-authentication on demand by means of an
Access-Challenge message sent from a server to a client. The
evaluator disagrees that this is likely to work for a given session
once an Access-Accept message has been received by the client. The
document claims "T", and the evaluator awards "F".
1.2.6 Authorization w/o Authentication - This requirement, as applied
to the protocol specification, mandates that non- necessary
authentication credentials not be required in a request for
authorization. The actual decision to provide authorization in the
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absence of any authentication resides in the application (e.g. AAA
server). RADIUS does require some form of credential in request
messages. The document [1] claims "F", and the evaluator concurs.
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - The document [1]
indicates that RADIUS can assign IPv4 addresses, and can easily be
extended to assign IPv6 addresses (see section 1.1.10). Of greater
concern, however, is the issue of static vs. dynamic addresses. If
dynamic address has the same meaning as it does for DHCP, then there
are issues of resource management that RADIUS has traditionally not
addressed. The document claims "P", and the evaluator concurs.
1.3.2 RADIUS Gateway Capability - The document [1] maintains that a
RADIUS++ to RADIUS gateway is pretty much a tautology. The document
claims "T", and the evaluator concurs.
1.3.3 Reject Capability - The document [1] maintains that RADIUS
Proxy Servers, and potentially RADIUS++ Routing Brokers, have the
ability to reject requests based on local policy. The document
claims "T" and the evaluator concurs.
1.3.4 Preclude Layer 2 Tunneling - The document [1] indicates that
[6] defines support for layer two tunneling in RADIUS. The document
claims "T", and the evaluator concurs.
1.3.5 Reauth on Demand - The document [1] indicates that RADIUS
provides this feature by means of the Session-Timeout and
Termination- Action attributes. While this may, in fact, be
sufficient to provide periodic re-authorization, it would not provide
re- authorization on demand. The protocol [2] does not address this
further. The document claims "P", and the evaluator awards "F".
1.3.6 Support for ACLs - The document [1] describes the attributes in
RADIUS that are used to convey the access controls described in [3].
Certain of these (e.g. QoS) are not currently defined in RADIUS, but
could easily be defined as new RADIUS attributes. The document
claims "P", and the evaluator concurs.
1.3.7 State Reconciliation - The document [1] addresses each of the
sub- items, as listed in the original AAA requirements document. In
reviewing the document against the modified requirements of [3],
there is still an issue with server-initiated state reconciliation
messages. While the protocol [2] makes provision for such messages,
as servers are allowed to initiate protocol dialogs, no detailed
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message formats are provided. This is an area that has traditionally
been a short coming of RADIUS. The document claims "P", and the
evaluator awards "F".
1.3.8 Unsolicited Disconnect - Much of the discussion from the
previous section applies to this section. The document [1] claims
"F", and the evaluator concurs.
1.4 Accounting Requirements
1.4.1 Real Time Accounting - RADIUS Accounting is widely deployed and
functions within the definition of real time contained in [3]. The
document [1] claims "T", and the evaluator concurs.
1.4.2 Mandatory Compact Encoding - RADIUS Accounting contains TLVs
for relevant accounting information, each of which is fairly compact.
Note that the term "bloated" in [3] is somewhat subjective. The
document [1] claims "T", and the evaluator concurs.
1.4.3 Accounting Record Extensibility - RADIUS Accounting may be
extended by means of new attributes or by using the Vendor-Specific
attribute. While it has been argued that the existing attribute
number space is too small for the required expansion capabilities,
the protocol [2] addresses this problem in section 3.0, and its
subsections, of [2]. The document [1] claims "T", and the evaluator
concurs.
1.4.4 Batch Accounting - RADIUS has no explicit provisions for batch
accounting, nor does the protocol [2] address how this feature might
be accomplished. The document [1] claims "F", and the evaluator
concurs.
1.4.5 Guaranteed Delivery - RADIUS Accounting is widely deployed and
provides guaranteed delivery within the context of the required
application-level acknowledgment. The document [1] claims "T", and
the evaluator concurs.
1.4.6 Accounting Timestamps - The document [1] indicates that this
feature is specified in [4] as the Event-Timestamp attribute. The
document claims [1] "T", and the evaluator concurs.
1.4.7 Dynamic Accounting - The document [1] indicates that this
requirement is partially met using the accounting interim update
message as specified in [4]. In addition, there was work in the
RADIUS WG regarding session accounting extensions that has not been
included in [4], i.e., some expired works in progress. The document
claims [1] "P", and the evaluator concurs.
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1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - The document [1]
claims "F", and the evaluator concurs.
1.5.2 Firewall Friendly - The document [1] indicates that RADIUS
deployment is know to have occurred in fire-walled environments. The
document claims "T", and the evaluator concurs.
1.5.3 Allocation of Local Home Agent - The document [1] claims "F",
and the evaluator concurs.
2. Summary Discussion
The document [1] and the protocol [2] suffer from having been written
in a short time frame. While the protocol does provide specific
guidance on certain issues, citing other relevant documents, it is
not a polished protocol specification, with detailed packet format
diagrams. There is a pool of prior work upon which the RADIUS++
protocol may draw, in that many of the concepts of Diameter were
first postulated as works in progress within the RADIUS WG, in an
attempt to "improve" the RADIUS protocol. All of these works in
progress have long since expired, however.
3. General Requirements
RADIUS++ meets many of the requirements of an AAA protocol, as it is
the current de facto and de jure standard for AAA. There are long-
standing deficiencies in RADIUS, which have been well documented in
the RADIUS and NASREQ WG proceedings. It is technically possible to
revamp RADIUS to solve these problems. One question that will be
asked, however, is: "What significant differences would there be
between a finished RADIUS++ protocol and the Diameter protocol?".
4. Summary Recommendation
Recommended in part. What may possibly be learned from this
submission is that it is feasible to have a more RADIUS-compliant
RADIUS-compatibility mode in Diameter.
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Evaluation of Diameter against the AAA Requirements
PRO Evaluation
Evaluator - Basavaraj Patil
Ref [1] is "Diameter Framework Document".
Ref [2] is "Diameter NASREQ Extensions".
Ref [3] is the AAA evaluation criteria as modified by us.
Ref [4] is "Diameter Accounting Extensions".
Ref [5] is "Diameter Mobile IP Extensions".
Ref [6] is "Diameter Base Protocol".
Ref [7] is "Diameter Strong Security Extension".
Ref [8] is "Comparison of Diameter Against AAA Network Access
Requirements".
The document uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance.
Evaluator's note : The Diameter compliance document [8] claims Total
"T" compliance with all the requirements except : - 1.2.5 - 1.5.2
Section 1 - Per item discussion
1.1 General Requirements
1.1.1 Scalability
Diameter is an evolution of RADIUS and has taken into consideration
all the lessons learned over many years that RADIUS has been in
service. The use of SCTP as the transport protocol reduces the need
for multiple proxy servers (Sec 3.1.1 Proxy Support of [1]) as well
as removing the need for application level acks. The use and support
of forwarding and redirect brokers enhances scalability. Evaluator
concurs with the "T" compliance on this requirement.
1.1.2 Fail-over
Again with the use of SCTP, Diameter is able to detect disconnect
indications upon which it switches to an alternate server (Sec 4.0
[6]). Also Requests and Responses do not have to follow the same
path and this increases the reliability. Evaluator concurs with the
"T" compliance on this requirement.
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1.1.3 Mutual Authentication
The compliance document quotes the use of symmetric transforms for
mutual authentication between the client and server (Sec 7.1 of
[6]). The use of IPSec as an underlying security mechanism and
thereby use the characteristics of IPSec itself to satisfy this
requirement is also quoted. Evaluator concurs with the "T"
compliance on this requirement.
1.1.4 Transmission Level Security
Although this requirement has been deprecated by the AAA evaluation
team the document complies with it based on the definition (referring
to hop-by-hop security). Section 7.1 of [6] provides the details of
how this is accomplished in Diameter. Evaluator concurs with the "T"
compliance on this requirement.
1.1.5 Data Object Confidentiality
This requirement seems to have come from Diameter. Ref [7] explains
in detail the use of Cryptographic Message Syntax (CMS) to achieve
data object confidentiality. A CMS-Data AVP is defined in [7].
Evaluator concurs with the "T" compliance on this requirement.
1.1.6 Data Object Integrity
Using the same argument as above and the hop-by-hop security feature
in the protocol this requirement is completely met by Diameter.
Evaluator concurs with the "T" compliance on this requirement.
1.1.7 Certificate Transport
Again with the use of the CMS-Data AVP, objects defined as these
types of attributes allow the transport of certificates. Evaluator
concurs with the "T" compliance on this requirement.
1.1.8 Reliable AAA Transport
Diameter recommends that the protocol be run over SCTP. SCTP
provides the features described for a reliable AAA transport.
Although the compliance is not a perfect fit for the definition of
this tag item, it is close enough and the functionality achieved by
using SCTP is the same. Evaluator concurs with the "T" compliance
on this requirement.
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1.1.9 Run over IPv4
Is an application layer protocol and does not depend on the
underlying version of IP. Evaluator concurs with the "T" compliance
on this requirement.
1.1.10 Run over IPv6
Is an application layer protocol and does not depend on the
underlying version of IP. Evaluator concurs with the "T" compliance
on this requirement.
1.1.11 Support Proxy and Routing Brokers
Section 3.1.1/2 of the framework document [1] provides an explanation
of how Diameter supports proxy and routing brokers. In fact it
almost appears as though the requirement for a routing broker came
from Diameter. Evaluator concurs with the "T" compliance on this
requirement.
1.1.12 Auditability
With the use of CMS-Data AVP [7] a trail is created when proxies are
involved in the transaction. This trail can provide auditability.
Evaluator concurs with the "T" compliance on this requirement.
1.1.13 Shared Secret Not Required
With the use of IPSec as the underlying security mechanism, Diameter
does not require the use of shared secrets for message
authentication. Evaluator concurs with the "T" compliance on this
requirement.
1.1.14 Ability to Carry Service Specific Attributes
The base protocol [6] is defined by Diameter and any one else can
define specific extensions on top of it. Other WGs in the IETF can
design an extension on the base protocol with specific attributes and
have them registered by IANA. Evaluator concurs with the "T"
compliance on this requirement.
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1.2 Authentication Requirements
1.2.1 NAI Support
The base protocol [6] defines an AVP that can be used to support
NAIs. Diameter goes one step further by doing Message forwarding
based on destination NAI AVPs. Evaluator concurs with the "T"
compliance on this requirement.
1.2.2 CHAP Support
Reference [2] section 3.0 describes the support for CHAP. Evaluator
concurs with the "T" compliance on this requirement.
1.2.3 EAP Support
Reference [2] section 4.0 describes the support for EAP. Evaluator
concurs with the "T" compliance on this requirement.
1.2.4 PAP/Clear-text Passwords
Reference [2] section 3.1.1.1 describes the support for PAP.
Evaluator concurs with the "T" compliance on this requirement.
1.2.5 Reauthentication on demand
The use of Session-Timeout AVP as the mechanism for reauthentication
is claimed by the compliance document. However no direct references
explaining this in the base protocol [6] document were found.
Evaluator deprecates the compliance on this to a "P"
Note: However this is a trivial issue.
1.2.6 Authorization w/o Authentication
Diameter allows requests to be sent without having any authentication
information included. A Request-type AVP is defined in [2] and it
can specify authorization only without containing any authentication.
Evaluator concurs with the "T" compliance on this requirement.
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1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment
The base protocol includes an AVP for carrying the address.
References [6.2.2 of 2] and [4.5 of 5] provide detailed explanations
of how this can be done. Evaluator concurs with the "T" compliance
on this requirement.
1.3.2 RADIUS Gateway Capability
One of the basic facets of Diameter is to support backward
compatibility and act as a RADIUS gateway in certain environments.
Evaluator concurs with the "T" compliance on this requirement.
1.3.3 Reject Capability
Based on the explanation provided in the compliance document for this
requirement evaluator concurs with the "T" compliance on this
requirement.
1.3.4 Preclude Layer 2 Tunneling
Ref [2] defines AVPs supporting L2 tunnels Evaluator concurs with
the "T" compliance on this requirement.
1.3.5 Reauth on Demand
A session timer defined in [6] is used for reauthorization. However
Diameter allows reauthorization at any time. Since this is a peer-
to-peer type of protocol any entity can initiate a reauthorization
request. Evaluator concurs with the "T" compliance on this
requirement.
1.3.6 Support for ACLs
Diameter defines two methods. One that supports backward
compatibility for RADIUS and another one with the use of a standard
AVP with the filters encoded in it. Evaluator concurs with the "T"
compliance on this requirement.
1.3.7 State Reconciliation
A long explanation on each of the points defined for this tag item in
the requirements document. Evaluator concurs with the "T" compliance
for this requirement.
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1.3.8 Unsolicited Disconnect
The base protocol [6] defines a set of session termination messages
which can be used for unsolicited disconnects. Evaluator concurs
with the "T" compliance on this requirement.
1.4 Accounting Requirements
1.4.1 Real Time Accounting
Evaluator concurs with the "T" compliance based on explanations in
[4].
1.4.2 Mandatory Compact Encoding
Use of Accounting Data Interchange Format (ADIF)-Record-AVP for
compact encoding of accounting data. Evaluator concurs with the "T"
compliance.
1.4.3 Accounting Record Extensibility
ADIF can be extended. Evaluator concurs with the "T" compliance.
1.4.4 Batch Accounting
Sec 1.2 of [4] provides support for batch accounting.
1.4.5 Guaranteed Delivery
Sections 2.1/2 of [4] describe messages that are used to guarantee
delivery of accounting records. Evaluator concurs with the "T"
compliance.
1.4.6 Accounting Timestamps
Timestamp AVP [6] is present in all accounting messages. Evaluator
concurs with the "T" compliance.
1.4.7 Dynamic Accounting
Interim accounting records equivalent to a call-in-progress can be
sent periodically. Evaluator concurs with the "T" compliance.
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1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages
Ref [5] provides details of how Diameter can encode MIP messages.
Evaluator concurs with the "T" compliance.
1.5.2 Firewall Friendly
Some handwaving here and a possible way of solving the firewall
problem with a Diameter proxy server. Document claims "T", evaluator
deprecates it to a "P"
1.5.3 Allocation of Local Home Agent
Diameter can assign a local home agent in a visited network in
conjunction with the FA in that network. Evaluator concurs with the
"T"
Summary Recommendation
Diameter is strongly recommended as the AAA protocol. The experience
gained from RADIUS deployments has been put to good use in the design
of this protocol. It has also been designed with extensibility in
mind thereby allowing different WGs to develop their own specific
extension to satisfy their requirements. With the use of SCTP as the
transport protocol, reliability is built in. Security has been
addressed in the design of the protocol and issues that were
discovered in RADIUS have been fixed. Diameter also is a session
based protocol which makes it more scalable. The support for
forwarding and redirect brokers is well defined and this greatly
improves the scalability aspect of the protocol.
Lastly the protocol has been implemented by at least a few people and
interop testing done. This in itself is a significant step and a
positive point for Diameter to be the AAA protocol.
Evaluation of Diameter against the AAA Requirements
CON Brief
Evaluator: Barney Wolff
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Section 1 - Per item discussion
1.1 General Requirements
1.1.1 Scalability - P (was T) The evaluator is concerned with
scalability to the small, not to the large. Diameter/SCTP may prove
difficult to retrofit to existing NAS equipment.
1.1.2 Fail-over - P (was T) SCTP gives an indication of peer
failure, but nothing in any Diameter or SCTP document the evaluator
was able to find even mentions how or when to switch back to a
primary server to which communication was lost. After a failure, the
state machines end in a CLOSED state and nothing seems to trigger
exit from that state. It was not clear whether a server, on
rebooting, would initiate an SCTP connection to all its configured
clients. If not, and in any case when the communication failure was
in the network rather than in the server, the client must itself,
after some interval, attempt to re-establish communication. But no
such guidance is given.
Of course, the requirement itself fails to mention the notion of
returning to a recovered primary. That is a defect in the
requirement. The evaluator has had unfortunate experience with a
vendor's RADIUS implementation that had exactly the defect that it
often failed to notice recovery of the primary.
1.1.3 Mutual Authentication - T
1.1.4 Transmission Level Security - T
1.1.5 Data Object Confidentiality - P (was T). Yes, the CMS data
type is supported. But the work in progress, "Diameter Strong
Security Extension", says:
Given that asymmetric transform operations are expensive, Diameter
servers MAY wish to use them only when dealing with inter-domain
servers, as shown in Figure 3. This configuration is normally
desirable since Diameter entities within a given administrative
domain MAY inherently trust each other. Further, it is desirable
to move this functionality to the edges, since NASes do not
necessarily have the CPU power to perform expensive cryptographic
operations.
Given all the fuss that has been made about "end-to-end"
confidentiality (which really means "NAS-to-home_server"), the
evaluator finds it absurd that the proposed solution is acknowledged
to be unsuited to the NAS.
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1.1.6 Data Object Integrity - P (was T). See above.
1.1.7 Certificate Transport - T
1.1.8 Reliable AAA Transport - T
1.1.9 Run over IPv4 - T
1.1.10 Run over IPv6 - T
1.1.11 Support Proxy and Routing Brokers - T
1.1.12 Auditability - T (based on our interpretation as non-
repudiation, rather than the definition given in reqts)
1.1.13 Shared Secret Not Required - T
1.1.14 Ability to Carry Service Specific Attributes - T
1.2 Authentication Requirements
1.2.1 NAI Support - T
1.2.2 CHAP Support - T
1.2.3 EAP Support - T
1.2.4 PAP/Clear-text Passwords - T
1.2.5 Reauthentication on demand - P (was T). No mechanism was
evident for the server to demand a reauthentication, based for
example on detection of suspicious behavior by the user. Session-
timeout is not sufficient, as it must be specified at the start.
1.2.6 Authorization w/o Authentication - T
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - T
1.3.2 RADIUS Gateway Capability - P (was T). RADIUS has evolved from
the version on which Diameter was based. EAP is a notable case where
the convention that the Diameter attribute number duplicates the
RADIUS one is violated. No protocol, not even RADIUS++, can claim a
T on this.
1.3.3 Reject Capability - T (The evaluator fails to understand how
any AAA protocol could rate anything other than T on this.)
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1.3.4 Preclude Layer 2 Tunneling - T
1.3.5 Reauth on Demand - P (was T). As with reauthentication, there
is no evident mechanism for the server to initiate this based on
conditions subsequent to the start of the session.
1.3.6 Support for ACLs - P (was T). The evaluator finds the Filter-
Rule AVP laughably inadequate to describe filters. For example, how
would it deal with restricting SMTP to a given server, unless all IP
options are forbidden so the IP header length is known? No real NAS
could have such an impoverished filter capability, or it would not
survive as a product.
1.3.7 State Reconciliation - P (was T). It is difficult for the
evaluator to understand how this is to work in a multi-administration
situation, or indeed in any proxy situation. Furthermore, SRQ with
no session-id is defined to ask for info on all sessions, not just
those "owned" by the requester.
1.3.8 Unsolicited Disconnect - T
1.4 Accounting Requirements
1.4.1 Real Time Accounting - T
1.4.2 Mandatory Compact Encoding - T
1.4.3 Accounting Record Extensibility - T
1.4.4 Batch Accounting - P (was T). The evaluator suspects that
simply sending multiple accounting records in a single request is not
how batch accounting should or will be done.
1.4.5 Guaranteed Delivery - T
1.4.6 Accounting Timestamps - T (The evaluator notes with amusement
that NTP time cycles in 2036, not 2038 as claimed in the Diameter
drafts. It's Unix time that will set the sign bit in 2038.)
1.4.7 Dynamic Accounting - T
1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - T
1.5.2 Firewall Friendly - F (was T). Until such time as firewalls
are extended to know about or proxy SCTP, it is very unlikely that
SCTP will be passed. Even then, the convenient feature of being able
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to send a request from any port, and get the reply back to that port,
means that a simple port filter will not be sufficient, and
statefulness will be required. Real friendship would require that
both source and dest ports be 1812.
1.5.3 Allocation of Local Home Agent - T
2. Summary Discussion
In some areas, Diameter is not completely thought through. In
general, real effort has gone into satisfying a stupendous range of
requirements.
3. General Requirements
Diameter certainly fails the KISS test. With SCTP, the drafts add up
to 382 pages - well over double the size of RADIUS even with
extensions. The evaluator sympathizes with the political instinct
when faced with a new requirement no matter how bizarre, to say "we
can do that" and add another piece of filigree. But the major places
where Diameter claims advantage over RADIUS, namely "end-to-end"
confidentiality and resource management, are just the places where
some hard work remains, if the problems are not indeed intractable.
More specifically, the evaluator sees no indication that specifying
the separate transport protocol provided any advantage to defray the
large increase in complexity. Application acks are still required,
and no benefit from the transport acks was evident to the evaluator.
Nor was there any obvious discussion of why "sequenced in-order"
delivery is required, when AAA requests are typically independent.
SCTP offers out-of-order delivery, but Diameter seems to have chosen
not to use that feature.
Whether TLV encoding or ASN.1/BER is superior is a religious
question, but Diameter manages to require both, if the "strong"
extension is implemented. The evaluator has a pet peeve with length
fields that include the header, making small length values invalid,
but that is a minor point.
Finally, interoperability would be greatly aided by defining a
standard "dictionary" format by which an implementation could adopt
wholesale a set of attributes, perhaps from another vendor, and at
least know how to display them. That is one of the advantages of
MIBs.
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4. Summary Recommendation
Diameter is clearly close enough to meeting the myriad requirements
that it is an acceptable candidate, though needing some polishing.
Whether the vast increase in complexity is worth the increase in
functionality over RADIUS is debatable.
Evaluation of COPS AAA Requirements
PRO Evaluation
Evaluator - David Nelson
Ref [1] is "Comparison of COPS Against the AAA NA Requirements", work
in progress, a.k.a. 'the document'
Ref [2] is RFC 2748 a.k.a. 'the protocol'
Ref [3] is the AAA evaluation criteria as modified by us.
Ref [4] is "AAA Protocols: Comparison between RADIUS, Diameter, and
COPS" work in progress.
Ref [5] is "COPS Usage for AAA", work in progress.
This document uses T to indicate total compliance, P to indicate
partial compliance and F to indicate no compliance.
Section 1 - Per item discussion
1.1 General Requirements
1.1.1 Scalability - The document [1] claims "T", and the evaluator
concurs.
1.1.2 Fail-over - The document [1] claims "T", and the evaluator
concurs.
1.1.3 Mutual Authentication - The document claims "T", and the
evaluator concurs.
1.1.4 Transmission Level Security - The document [1] indicates that
transmission layer security, as defined in [3], is provided in the
protocol, using the mechanisms described in [2]. It should be noted
that this requirement is now a SHOULD in [3]. The document claims
"T", and the evaluator concurs.
1.1.5 Data Object Confidentiality - The document [1] indicates that
end-to-end confidentiality is provided using a CMS-data attribute,
based in large part upon RFC 2630. The evaluator has not, at this
time, investigated the applicability of RFC 2630 to the AAA work.
The document claims "T", and the evaluator concurs.
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1.1.6 Data Object Integrity - The document [1] indicates that data
object integrity is provided using a CMS-data attribute, based in
large part upon RFC 2630. The evaluator has not, at this time,
investigated the applicability of RFC 2630 to the AAA work. The
document claims "T", and the evaluator concurs.
1.1.7 Certificate Transport - The document [1] indicates that
certificate transport is provided using a CMS-data attribute, based
in large part upon RFC 2630 and RFC 1510. The evaluator has not, at
this time, investigated the applicability of RFC 2630 to the AAA
work. The document claims "T", and the evaluator concurs.
1.1.8 Reliable AAA Transport - The document [1] indicates that COPS
uses TCP, which certainly meets the requirements for a reliable
transport. The document claims "T", and the evaluator concurs.
1.1.9 Run over IPv4 - The document [1] claims "T", and the evaluator
concurs.
1.1.10 Run over IPv6 - The document [1] claims "T", and the evaluator
concurs.
1.1.11 Support Proxy and Routing Brokers - Reasonable detail of proxy
operations is provided in [5]. The document [1] claims "T", and the
evaluator concurs.
1.1.12 Auditability - The document [1] alludes to a History PIB that
would enable auditing without explaining how it would work. The AAA
Extension [5] does not provide additional insight. The document
claims "T", and the evaluator awards "P".
1.1.13 Shared Secret Not Required - The document [1] claims "T" and
the evaluator concurs.
1.1.14 Ability to Carry Service Specific Attributes - The document
[1] claims "T", and the evaluator concurs.
1.2 Authentication Requirements
1.2.1 NAI Support - The document [1] indicates that NAI is to be
supported in the Information Model, but notes that for cases where
certificates are in use, the more restrictive syntax of RFC 2459
applies. The document claims "T", and the evaluator awards "P".
1.2.2 CHAP Support - The document [1] claims "T", and the evaluator
concurs.
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1.2.3 EAP Support - The document [1] claims "T", and the evaluator
concurs.
1.2.4 PAP/Clear-text Passwords - The document [1] indicates
compliance, presumably using a CMS-data attribute, based in large
part upon RFC 2630. The evaluator has not, at this time,
investigated the applicability of RFC 2630 to the AAA work. The
document claims "T", and the evaluator concurs.
1.2.5 Reauthentication on demand - The document [1] claims "T", and
the evaluator concurs.
1.2.6 Authorization w/o Authentication - This requirement, as applied
to the protocol specification, mandates that non- necessary
authentication credentials not be required in a request for
authorization. The actual decision to provide authorization in the
absence of any authentication resides in the application (e.g. AAA
server). The document [1] claims "T", and the evaluator concurs.
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - The document [1]
claims "T", and the evaluator concurs.
1.3.2 RADIUS Gateway Capability - The document [1] claims "T", and in
the absence of any detailed discussion of how this is accomplished,
in either [1] or [5], the evaluator awards "P".
1.3.3 Reject Capability - The document claims [1] "T" and the
evaluator concurs.
1.3.4 Preclude Layer 2 Tunneling - The document [1] claims "T", and
in the absence of any detailed discussion of how this is
accomplished, in either [1] or [5], the evaluator awards "P".
1.3.5 Reauth on Demand - The document [1] claims "T", and the
evaluator concurs.
1.3.6 Support for ACLs - The document [1] "T", and the evaluator
concurs.
1.3.7 State Reconciliation - The document [1] "T", and the evaluator
concurs.
1.3.8 Unsolicited Disconnect - The document [1] claims "T", and the
evaluator concurs.
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1.4 Accounting Requirements
1.4.1 Real Time Accounting - The document [1] claims "T", and the
evaluator concurs.
1.4.2 Mandatory Compact Encoding - Note that the term "bloated" in
[3] is somewhat subjective. The document [1] claims "T", and the
evaluator concurs.
1.4.3 Accounting Record Extensibility - The document [1] claims "T",
and the evaluator concurs.
1.4.4 Batch Accounting - The protocol [2] [5] does not address how in
detail this feature might be accomplished. The document [1] claims
"T", and the awards "P".
1.4.5 Guaranteed Delivery - Guaranteed delivery is provided by TCP.
The document [1] claims "T", and the evaluator concurs.
1.4.6 Accounting Timestamps - The document [1] claims "T", and the
evaluator concurs.
1.4.7 Dynamic Accounting - The document [1] claims "T", and the
evaluator concurs.
1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - The document [1]
claims "T", and the evaluator concurs.
1.5.2 Firewall Friendly - The document [1] claims "T", and the
evaluator concurs.
1.5.3 Allocation of Local Home Agent - The document [1] claims "T",
and the evaluator concurs.
2. Summary Discussion
It may appear, upon initial inspection, that the evaluator has not
lent a critical eye to the compliance assertions of the document [1].
First, this memo is a "PRO" brief, and as such reasonable benefit of
doubt is to be given in favor of the protocol submission. Second,
there is a fundamental conceptual issue at play. The COPS-PR model
provides a sufficient set of basic operations and commands, a
stateful model, the ability for either "peer" to initiate certain
kinds of requests, as well as an extensible command set, to be able
to support a wide variety of network and resource management
protocols. The details of protocol specific messages is left to
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Policy Information Base (PIB) data objects. Since no AAA PIB has
been written, the evacuator can only (optimistically) assess the
inherent capabilities of the base protocol to accomplish the intended
requirements of [3], given a reasonable set of assumptions about what
an AAA PIB might look like.
In some sense, this akin to asserting that a given algorithm can be
correctly implemented in a specific programming language, without
actually providing the code.
The PIB model used by COPS is a powerful and flexible model. The
protocol document [5] spends a considerable amount of time
enumerating and describing the benefits of this data model, and
explaining its roots in Object Oriented (OO) design methodology.
Analogies are made to class inheritance and class containment, among
others. It's always hard to say bad things about OO.
3. General Requirements
COPS-AAA would appear to meet (totally or partially) all of the
requirements of [3], at least as can be determined without the
benefit of an AAA PIB.
4. Summary Recommendation
Recommended with reservation. Before final acceptance of COPS-AAA,
someone is going to have to write the AAA PIB and evaluate its
details.
Evaluation of COPS against the AAA Requirements
CON Evaluation
Evaluator - David Mitton
The Primary document discussed here is [COPSComp] and the arguments
therein based on the proposal [COPSAAA].
[COPSComp] "Comparison of COPS Against the AAA NA Requirements", Work
in Progress.
[COPSAAA] "COPS Usage for AAA", Work in Progress.
[EksteinProtoComp] "AAA Protocols: Comparison between RADIUS,
Diameter, and COPS", Work in Progress.
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References: (in order of relevancy)
[COPSBase] Durham, D., Boyle, J., Cohen, R., Herzog, S., Rajan, R.
and A. Sastry, "The Common Open Policy Service Protocol",
RFC 2748, January 2000.
[COPSFwork] Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework
for Policy-based Admission Control", RFC 2753, January
2000.
[COPSPR] "COPS Usage for Policy Provisioning", Work in Progress.
[COPSSPPI] "Structure of Policy Provisioning Information (SPPI)",
Work in Progress.
[COPSCMS] "COPS Over CMS", Work in Progress.
[COPSTLS] "COPS Over TLS", Work in Progress.
[COPSGSS] "COPS Extension for GSS-API based Authentication
Support", Work in Progress.
Other COPS & RSVP RFCs & drafts not listed as not directly relevant.
Compliance: T==Total, P==Partial, F=Failed
Section 1 - Per item discussion
Initial Note: [COPSComp] claims "unconditional compliance" with all
requirements.
1.1 General Requirements
1.1.1 Scalability - P (was T) The evaluator is concerned with
scalability of many always-on TCP connections to a server supporting
a lot of clients, particularly with the heartbeat messages. The
claim that the request handle is "unbounded" sounds fishy.
1.1.2 Fail-over - P (was T) COPS gives an indication of peer failure,
and has mechanisms to restart state, but there seems to be a bias
toward a single state server. COPS has decided that synchronizing
state between multiple hot servers is out of scope.
Because COPS uses TCP, it is at the mercy of the TCP timers of the
implementation which can be significant. Connection timeout
reporting to the application may be delayed beyond the client
authentication timeouts. Tuning the Keep-Alive message to a tighter
period will increase the session and system overhead.
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1.1.3 Mutual Authentication - P (was T) The explanation is sort of
for message object integrity. It does not describe authentication
techniques. The evaluator assumes that COPS peers would authenticate
each other at Client-Open time. But cannot understand how this would
work if proxies are involved.
1.1.4 Transmission Level Security - T
1.1.5 Data Object Confidentiality - T Seems almost a carbon copy of
the Diameter capabilities. This evaluator echoes the high overhead
concerns of the Diameter evaluator for the CMS capability. TLS is
not mentioned here, but is piled on later.
1.1.6 Data Object Integrity - T See above.
1.1.7 Certificate Transport - T
1.1.8 Reliable AAA Transport - T (maybe P) COPS meets this
requirement as well as any other protocol we've evaluated. That is
it does have one application level ACK. Statements such as "TCP
provides guaranteed delivery" are incorrect. COPS does attempt to
identify outages by using a keep-alive message between TCP peers.
1.1.9 Run over IPv4 - T
1.1.10 Run over IPv6 - T
1.1.11 Support Proxy and Routing Brokers - P (was T) How client
types are supported forward is not well understood by this evaluator.
Does each client type require the Broker to make a different client
Open request to it's upstream servers? What about routing brokers?
1.1.12 Auditability - P (was T) (based on our interpretation as
non-repudiation, rather than the definition given in reqts) The
explanation of a History PIB is incomplete and therefore
inconclusive.
1.1.13 Shared Secret Not Required - T Except this clause in
[COPSAAA] 6.2 page 14 "COPS MUST be capable of supporting TLS"
1.1.14 Ability to Carry Service Specific Attributes - P (was T)
a) COPS only allows a small number of unique objects to be added.
256 Object "classes" or types, with 256 subtypes or versions.
Client types are 16 bits long, where the high bit indicates
"enterprise" specific values. But pertain to a COPS peer-
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connection session. The client type seems to just identify the
information model for the message. eg. it will be fixed to one
value for AAA.
b) Service specific objects are not the same as Vendor Specific
Objects. They pertain to objects within a client type.
c) The PIB model leads to a different model interoperability.
Because most vendor product differ in some way, each PIB will be
different, and sharing common provisioning profiles will be a
rather difficult mapping problem on the server.
d) It's not clear the different client types can be mixed or that
other objects definitions can be used from other defined client
types. It's really unclear how the client type of a connection
propagates in a proxy situation.
1.2 Authentication Requirements
1.2.1 NAI Support - T The requirement that RFC 2459 (X.509 profiles)
be met presumes that Auth servers would not have a mapping or local
transformation.
1.2.2 CHAP Support - T An Information Model is being invoked, which
I don't see really fleshed out anywhere. [COPSAAA] does a bit of
handwaving and definitions but doesn't deliver much meat.
Nonetheless, this could be handled ala RADIUS.
1.2.3 EAP Support - P (was T) Again with the non-existent
Information Model. To do EAP, this evaluator thinks another Request
or Decision type is needed here to indicate to proxies that an
extended message exchange is in progress.
1.2.4 PAP/Clear-text Passwords - T
1.2.5 Reauthentication on demand - T
1.2.6 Authorization w/o Authentication - T
The comment "Please note: with existing algorithms, any authorization
scheme not based on prior authentication is meaningless" is
meaningless out of application context.
1.3 Authorization Requirements
1.3.1 Static and Dynamic IP Addr Assignment - T
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1.3.2 RADIUS Gateway Capability - P (was T). It would be interesting
to see RADIUS attributes wrapped in some COPS "Information Model".
1.3.3 Reject Capability - T
1.3.4 Preclude Layer 2 Tunneling - T
More work for the "Information Model" author!
1.3.5 Reauthorization on Demand - T
1.3.6 Support for Access Rules & Filters - P (was T) Yet more work
for the "Information Model" author, including some design issues
which alluded the RADIUS and Diameter designers. At least an attempt
was made in Diameter. There is nothing here.
1.3.7 State Reconciliation - P (was T). It is difficult for the
evaluator to understand how well the COPS mechanisms work in a
multi-administration situation, or in any proxy situation. Multi-
server coordination, if allowed, seems to be lacking a description.
1.3.8 Unsolicited Disconnect - T
1.4 Accounting Requirements
1.4.1 Real Time Accounting - T
1.4.2 Mandatory Compact Encoding - T This evaluator does not believe
that ADIF is a compact format. But does believe that the Information
Model author can design a PIB with accounting statistics that will
satisfy this requirement.
1.4.3 Accounting Record Extensibility - P (was T) By defining a
vendor/device specific PIB for additional elements.
1.4.4 Batch Accounting - P (was T) Offered description does not seem
to match the requirement.
1.4.5 Guaranteed Delivery - P (was T) TCP does NOT "guarantee
delivery", only application Acks can do that. If these acks can be
generated similar to the description here, then this requirement is
met.
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1.4.6 Accounting Timestamps - T Another item for the "Information
Model" author.
1.4.7 Dynamic Accounting - T Event and interim accounting can be
supported.
1.5 MOBILE IP Requirements
1.5.1 Encoding of MOBILE IP Registration Messages - P (was T) Yet
more work for the "Information Model" author. Hope he can handle it.
1.5.2 Firewall Friendly - P (was T) I guess. Because it uses TCP
and can be identified by known connection port. But there is an
issue with respect to the impact level of mixed COPS traffic coming
through a common firewall port.
1.5.3 Allocation of Local Home Agent - P (was T) Just add another
element to that "Information Model" definition.
2. Summary Discussion
COPS was designed to do some things similar to what we want and be
somewhat flexible, but with a totally different set of assumptions on
how many clients and requests would be funneled through the
infrastructure and the acceptable overhead. This evaluator is not
sure that it scales well to the fast evolving access market where
every product doesn't implement a small set of common features, but a
large set of overlapping ones.
3. General Requirements
COPS started out with small and easily met set of design goals for
RSVP and DiffServe, and is evolving as a new hammer to hit other
nails [COPSPR]. As COPS implementors get more operational
experience, it is interesting to see more reliability fixes/features
quickly get patched in.
Understanding COPS requires that you read a number RFCs and drafts
which do not readily integrate well together. Each application of
COPS has spawned a number of drafts. It's not clear if one wants to
or can implement a single COPS server that can service AAA and other
application clients.
The COPS authors seem to overly believe in the goodness of TCP, and
rely on it to solve all their transport problems, with concessions to
application keep-alive messages to probe the connection status and
sequence numbers to prevent replay attacks. This evaluator believes
this type of approach may work for many networks but really doesn't
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scale well in larger configurations. End-to-end application acks are
the only guaranteed delivery solution, particularly where distributed
state is involved.
COPS falls into an in between place on encoding. It has small number
of simple data object blobs which are concatenated ala
RADIUS/Diameter TLVs to form a flexible message layout. However,
they attempt to limit the number of objects by making them
arbitrarily complex ala SNMP MIBs, and defining yet another data
structuring language for these PIBs. There is a lot of computer
science style grandstanding in [COPSAAA] Section 1.2, but no
translation into how a set of data objects can be used to meet these
wonderful features in operation. (or even if we needed them) This
will be the crux of the interoperability issue. RADIUS
implementations interoperate because they at least, understand a
common set of functional attributes from the RFCs. And vendor extent
ions can be simply customized in as needed via dictionaries. If PIB
definitions are needed for every piece and version of access
equipment, before you can use it, then the bar for ease of
configuration and use has been raised quite high.
Support for PIB definition and vendor extensions will be on the same
order as MIB integration in SNMP management products and put the
supposed complexity of Diameter to shame.
4. Summary Recommendation
COPS has a structure that could be made to serve as a AAA protocol,
perhaps by just copying the features of RADIUS and Diameter into it.
The author of [COPSAAA] and [COPSComp] has not done the whole job yet
and some of the missing pieces are vexing even for those already in
the field.
While some of the synergy with other COPS services is attractive,
this evaluator is concerned about the liabilities of combining AAA
services with the new emerging COPS applications in a single server
entity will introduce more complexity than needed and opportunities
to have progress pulled into other rat-holes. (eg. Policy Frameworks)
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Appendix D - Meeting Notes
The minutes of the team meetings as recorded by various members.
Recorded by: Mark Stevens
Arguments for and against SNMP as an AAA protocol were given. Stuart
Barkley gave a summary of the pro argument. Mike St. Johns gave a
summary of the con argument. Dave Nelson asked for "instructions to
the jury" in an effort to determine what evidence could and could not
be used in making decisions.
The AAA evaluation criteria is weak in some areas and in others it
appears to be written with what might be interpreted as undue
influence from the NASREQ working group.
Mike St. Johns offered that we must restrict ourselves to considering
only the evidence provided in the compliance documents and any
supporting documents to which they may refer.
In summary: AAA evaluation criteria document, AAA evaluation criteria
source documents, protocol response documents and reference
documents.
The question as to what the group should do with malformed
requirements came up. The consensus seemed to be that we would use
the requirements as adjusted in our last meeting where the
requirements made no sense.
The floor was then given to Stuart Barkley for the pro SNMP argument.
Highlights:
* In most areas the requirements are met by SNMP.
* Confidentiality and Certificate transport mechanisms may be weak,
but workable.
* With regard to Authentication, every technique can be supported
although support for PAP or cleartext passwords is weak.
* With regard to Authorization, there is nothing in the requirements
that cannot be supported.
* Accounting everything supported, although there is no specific
consideration for compact encoding. SNMP not as bloated as ASCII
or XML based encoding schemes. Requirement for compact encoding
weakly indicated in requirements anyway. Server-specific
attributes needed, but compact encoding preclude w/o tradeoffs.
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* With regard to mobile IP requirement, everything works well,
although firewall friendliness is a judgment call.
* Proxy mechanisms of SNMPv3 mitigates problems w/ firewalls.
* Scalability is ok.
* Overall, meets most requirements and shortfalls are minor.
* In some cases requirements seemed to expressed in a manner that
"stacks" the odds against SNMP.
* SNMP is deployed everywhere already.
* The protocol has a well-understood behavior despite the tedium of
MIB definition, so it has the advantage of not requiring the
creation of a new infrastructure.
* AAA response document is silent on architecture and MIB
definition, but there is too much work to do at this stage of
evaluation. Not having done the MIB definitions and architecture
is not a limitation of the protocol.
* SNMP is a good candidate.
Mike St. Johns took the floor to give a summary of the con argument.
* Neither the requirements, core documents nor response document
specify the mechanism of operation.
* Liberties were taken in the assertion that the server to server
interaction requirements were met.
* The scaling arguments are weak.
* Fail-over arguments are weak.
* Security aspects work well with the manager/server paradigm, but
not well in bidirectional interactions among peers.
* The authentication requirements not understood by authors of the
response document. * SNMP is just data moving protocol.
* Message formats not specified.
* What is the method for supporting authentication? Storing the
information is handled, but what do the nodes do with it?
* The protocol certainly shined in the area of meeting accounting
requirements.
* Although SNMP could certainly play a role in the accounting space,
it is unusable in the areas of Authorization and Authentication.
* The response document does not address how the problem will be
solved.
* It does not address the scalability issues that may arise in the
transition from a manager-agent mode of operation to a client-
server model.
The group then examined each requirement against SNMP in a line-by-
line exercise.
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Attendees - All (Mike St. John, Dave Mitton, Dave Nelson, Mark
Stevens, Barney Wolff, Stuart Barkley, Steven Crain, Basavaraj Patil)
Minutes recorded by : Basavaraj Patil
Evaluation of RADIUS++ AAA Requirements
Pro : Mark Stevens
Con : Dave Nelson
- Question raised on if all meetings held so far have been recorded.
Last week's meeting was recorded by Mark. Previous meetings have
been recorded by Mike. All of these minutes should be available
in the archive.
- Dave Nelson mentioned that Pat Calhoun has responded on the AAA WG
mailing list to the changes made to the requirements document by
the evaluation team. Pat's response includes arguments for
inclusion of some of the requirements that were deleted by the
eval team.
- Mike concluded that we can reinstate these requirements after
reviewing Pat's comments in detail and the RFCs referenced. The
intent is to take Pat's comments/document and review it between
now and next Thursday (July 6th) and integrate the comments based
on the findings at that time.
Voting Procedure for evaluation : No voting during the discussion.
All votes MUST be submitted to Mike by COB, June 28th, 00.
- Dave Nelson's summary of the Con statement for RADIUS++.
Overview of the points on which the evaluator disagrees with the
compliance statement.
Conclusion from Dave : Not recommended (Details in the con
statement).
Q: Is it possible to use it for accounting?
A: Authentication and Authorization could be separated, but
Accounting is the weak link in this protocol and hence is not
suitable.
- Mark Steven's summary of the Pro statement
Agreed with most of the observations made by Dave Nelson. The
biggest thing going for it is that it has been running in this
environment for a while and it does meet most of the requirements
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in the document. Transition will be easy and backwards
compatibility is a key plus point.
Point-by-point Discussion:
General (1.1):
1.1.1 Scalability
BW - There is no actual limit on the number of outstanding requests.
The protocol itself does not limit the number.
DN -Simultaneous requests is not the same as outstanding requests.
Discussion of workarounds that have been implemented to overcome this
problem.
1.1.2 Fail-over
DN - This is an application layer protocol and uses application level
time-outs to provide fail-over solutions. Analogy and discussion on
the use of round-trip-timer in TCP.
Example of how robust a network can be based on a machine at MIT that
was decommissioned and a new one with the same name installed in the
network.
Discussion of environments where proxies for primary, secondary and
tertiaries exist and the possible effect of flooding messages in the
event of a fail-over detection.
1.1.3 Mutual Authentication
No Discussion. Accepted as stated.
1.1.4 Transmission level security
This requirement was deleted from the list by the evaluation team.
It was deleted because it is an overgeneralization of Roam Ops.
DN - There is a concern regarding what this really means. Referred
to what Pat is saying about this on the list and the need for it to
be reinstated.
Suggestion to change the tag in the requirements document to hop-by-
hop security.
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Does the Roamops group use transmission level security to imply hop-
by-hop security?
1.1.5 Data Object Confidentiality
Mike explained the concept of Cryptographic Message Syntax (CMS -
RFC2630). There are some issues regarding the use of CMS at an end
point. Symmetric or Asymmetric keys can be used.
There does not seem to be a problem with the suggested usage of CMS
in RADIUS++.
1.1.6/7 Data Object Integrity/Certificate Transport
No discussion. (I guess everyone concurs with the statement in the
compliance document and the reviewers comments).
1.1.8 Reliable AAA Transport
BW - Radius provides reliability at the application layer by doing
retransmissions. So why is there a need for a reliable AAA transport
protocol?
- Is it packet loss that the protocol needs to be concerned about?
DN - This requirement is tied to the failover issue. Explanation of
the negative impact of retransmissions in a network, especially in
the case of a web of proxies.
Conclusion is that this requirement deals with packet loss.
1.1.9/10 Run over IPv4/6
Running over IPv6 should be a trivial issue.
1.1.11 Support Proxy and Routing Brokers
- Discussion on what this requirement means and analogy to DNS
servers in a network.
- RADIUS can be extended to support this requirement and from the
compliance document this does not appear to be fully cooked yet.
1.1.12 Auditability
No Discussion
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1.1.13 Shared Secret Not Required
This seems to be a trivial issue to be addressed in RADIUS++.
1.1.14 Ability to carry Service Specific Attributes
No Discussion
Authentication Requirements:
1.2.1 NAI Support
Trivial - Total compliance.
1.2.2 CHAP Support
Comment : RADIUS support of CHAP could be better and the response
needs to be encrypted.
1.2.3/4 EAP/PAP
No Discussion
1.2.5 Reauthentication on Demand
DN - Document claims that the server can reauthenticate by issuing an
Access-challenge. There is a change to the state machine and the
suggested solution is too simplistic. Also backwards compatibility
would be an issue.
1.2.6 Authorization w/o Authentication
DN - This is trivial to fix, but this is not mentioned in the
compliance document.
Authorization Requirements:
1.3.1 Static and Dynamic IP Addr assignment
- RADIUS does not rise to the demands of being a resource manager
- RADIUS assigns an address and it stays assigned for the session.
There is no concept of leasing.
1.3.2 RADIUS Gateway Capability
This is a requirement written that is not applicable to RADIUS
itself.
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1.3.3/4/5/6/7/8
Call dropped. Somebody else needs to fill in here. (Mike ????)
Accounting Requirements:
1.4.1 Real time accounting
No dissent. No discussion
1.4.2 Mandatory compact encoding
Comment made regarding ASN.1 and XML in this context
1.4.3 Accounting Record Extensibility
No discussion
1.4.4 Batch Accounting
No specific wording in the document to show how this can be done.
Basically it is real time accounting without the real time
constraint.
It may be a trivial issue.
1.4.5/6 Guaranteed Delivery/Accounting Timestamps
No Discussion
1.4.7 Dynamic Accounting
There is ongoing discussion in the AAA WG on this requirement. The
RADIUS WG is also discussing this (comment). The idea here is to be
able to send the equivalent of a phonecall in progress type of
messages.
Mobile IP Requirements:
1.5.1 Encoding of Mobile IP Reg. Messages
May be trivial. Discussion on what this requirement really is. Is
it just the ability to carry the reg. message as payload? Does the
AAA protocol have to delve into the reg. message and behave
differently.
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1.5.2 Firewall Friendly
No Discussion
1.5.3 Allocation of Local Home Agents
This concept needs to be clarified as the author writing the
compliance statement did not understand it either.
If you notice anything that I recorded here as something
misinterpreted, please feel free to make corrections.
Attendees: Mike St. John, Dave Mitton, Dave Nelson, Barney Wolff,
Stuart Barkley, Steven Crain, Basavaraj Patil.
Missing: Mark Stevens.
Minutes recorded by: Stuart Barkley
Evaluation of Diameter AAA Requirements
Advocates:
Pro: Basavaraj Patil
Con: Barney Wolff
Summary discussion:
PRO summary (Basavaraj Patil):
session based
lightweight base + extensions
has implementation experience
based upon radius
fixes specific problems with radius,
interoperates with radius
looks like requirements are written for diameter
CON summary (Barney Wolff):
meets most needs, designed with requirements in mind
issues: scalability in small devices (strong crypto specifically)
failover (need guidance on failover recovery procedures)
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Data object confidentiality has been expressed as very important,
diameter glosses over it referring to rfc2630, cost to run on NAS
device
ACL: filter style syntax seems inadequate
state reconciliation: difficult over global multiple
administrative domains
batch accounting: implementation doesn't meet intended need
firewall friendly: until firewalls support SCTP will be failure
summary very close
concerns:
size and complexity needs almost all extensions to actually support
needs separation of SCTP and data (as per IESG suggestion?)
application vs transport acks
Point-by-point Discussion:
General (1.1):
1.1.1 Scalability
Handles large number of requests
SCTP reduces proxy needs (how? what is justification for this
statement?)
Scalability in large
1.1.2 Fail-over
Recovery from SCTP failure needs discussion (Note to DM: Include
in final document considerations)
1.1.3 Mutual Authentication
No Discussion
1.1.4 Transmission level security
No Discussion
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1.1.5/6 Data Object Confidentiality/Data Object Integrity
Crypto in NAS
NAS needs knowledge of when to use crypto
One Time Passwords
1.1.7 Certificate Transport
No Discussion
1.1.8 Reliable AAA Transport
No Discussion
1.1.9/10 Run over IPv4/6
No Discussion
1.1.11 Support Proxy and Routing Brokers
No Discussion
1.1.12 Auditability
No Discussion
1.1.13 Shared Secret Not Required
No Discussion
1.1.14 Ability to carry Service Specific Attributes
No Discussion
Authentication Requirements:
1.2.1 NAI Support
No Discussion
1.2.2 CHAP Support
No Discussion
1.2.3/4 EAP/PAP
No Discussion
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1.2.5 Reauthentication on Demand
No Discussion
1.2.6 Authorization w/o Authentication
No Discussion
Authorization Requirements:
1.3.1 Static and Dynamic IP Addr assignment
No Discussion
1.3.2 RADIUS Gateway Capability
Protocol requirement or implementation/application requirement?
Which RADIUS versions are to be supported? Which subset?
1.3.3 Reject Capability
No Discussion
1.3.4 Preclude L2TP
No Discussion
1.3.5 Reauthorize on demand
Raj to look at this again
1.3.6 Support for ACLs
Standardizes syntax not semantics.
Standardizes semantics in NASREQ extension, but is very weak
1.3.7 State reconciliation
Appears to be weak in that server must "query the world" to
restore its state
Just in time reconciliation
Simultaneous usage limitations
More discussion needed
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1.3.8 Unsolicited disconnect
No Discussion
Accounting Requirements:
1.4.1 Real time accounting
No Discussion
1.4.2 Mandatory compact encoding
Is ADIF compact?
Is ADIF UTF-8 compatible?
1.4.3 Accounting Record Extensibility
No Discussion
1.4.4 Batch Accounting
Diameter okay for small batches. Specification doesn't seem
suitable for large batch transfers (100,000+ records)
1.4.5 Guaranteed Delivery
No Discussion
1.4.6 Accounting Timestamps
No Discussion
1.4.7 Dynamic Accounting
No Discussion
Mobile IP Requirements:
1.5.1 Encoding of Mobile IP Reg. Messages
Taken of faith
1.5.2 Firewall Friendly
Issues with SCTP being supported initially through firewalls
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1.5.3 Allocation of Local Home Agents
Still lack of understanding of the AAA protocol requirements here
(versus just being a roaming attribute)
Overall summary:
Diameter seems to meet most requirements and is a likely candidate to
support AAA requirements.
Other matters:
Votes on Diameter should be in by Sunday evening. Same format as
before. Mike will tally up as both majority and average votes.
Should different requirements have different weight?
Possibility of SNMP reconsideration as per ADs? To close off our
task in timeframe allocated, should not reopen submissions or
discussions. Could cause to drag on for long time causing us to miss
our July 15 date.
Possibility of needing a few extra days to finish report due to
editing and review needs of the group. Mike to ask ADs to consider
slight time extension possibility.
"No discussion" means that the topic was mentioned but there we no
objections/issues raised on that requirement being met.
These are based upon my notes. Please send any corrections to the
list.
Minutes of AAA-Team Telecon 7/6/00
By: Barney Wolff
Pro review of COPS - Dave Nelson
Likes the object model.
No apparent showstoppers.
Will resend review with typos corrected.
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Con review of COPS - Dave Mitton
Architecture is mostly there.
Strong dependency on info model, sceptical of object model.
Problem with info model in multi-vendor, multi-administration
environment.
How does server speak to multiple client flavors?
Will resend review with typos corrected.
Comment by Mike StJ "replace SNMP with COPS" - :) I think.
Per-Item discussion
1.1.1 Scalability - concern re always-on TCP. Direction to DM - add
general issue of number of connections.
1.1.2 Failover - No hot backup, but true of all protocols. (ie, no
explicit mention of server-server protocol that might keep a backup
server in sync so it could take over instantly.)
1.1.3 Mutual Authentication - perhaps relies on TLS. Draft does not
otherwise support this.
1.1.8 Reliable AAA Transport - TCP + appl heartbeat.
1.1.11 Proxy & Routing Brokers - client-type interaction with proxy
is questionable. (In later discussion, it appears client-type is a
field in the request, and perhaps all AAA is one type, so may not be
an issue.)
1.1.13 Shared secret not req'd - runs over TLS, no multiple levels of
security.
1.2.1 NAI Support - some uncertainty on the impact of RFC 2459 (X.509
profiles) on this - may restrict NAI in some way?
1.2.3 EAP Support - multi-pass handshake needs work.
1.2.6 Authorization without Authentication - Mike comments the
requirement is broken. BW comment (post-meeting) - the requirement
appears intended specifically to chastise RADIUS for requiring User-
Name and some sort of password in an Access-Request, even if it's
sent pre-connect, on receipt of DNIS, for example. Sure it's silly,
but does it really matter whether an attribute is absent or filled
with "NONE"? This was just nasty sniping at RADIUS on somebody's
part, imho.
1.3.2 RADIUS Gateway - skepticism was expressed.
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1.3.4 Preclude L2 Tunnels - too much handwaving.
1.3.6 Access Rules - lots of work needed.
1.3.7 State Reconciliation - multi-server coordination is an issue.
1.4.4 Batch Accounting - for small batches, perhaps.
1.4.5 Guaranteed Delivery - application acks are an area of mystery.
1.5.2 Firewall-Friendly - COPS like any Swiss-Army-Knife protocol
(SNMP) requires the firewall to look inside the packets, because
passing AAA may be allowed but not other protocol uses. So it would
be a big help, for both COPS and SNMP, to define a different port for
its AAA application.
Present: Mike, Bernard, Paul, Bert, Raj, Dave N., Dave M., Barney,
Stuart, Mark
Recorded By: Dave Nelson
Mike St. Johns set the ground rules.
An item by item review of the summary results was held.
1.1.1 Question as to why SNMP and RADIUS++ are "P"? There are issues
regarding scaling of retries in a web of proxies (multi-layer proxy;
primary, secondary tertiary servers at each level).
1.1.2 No protocol did very well. Similar issues as above, e.g. web
of proxies. Recovery of state from a previously failed primary
server?
1.1.3 Question as to how serious is the need for this requirement?
May be some legitimate requirements from Mobile IP. Is this
requirement an AAA-level issue?
1.1.4 Called hop-by-hop or transmission level?
1.1.5 Most protocols evaluated used CMS to meet this requirement.
Question as to applicability of CMS for NASes and other edge devices?
There is a requirement for object by object confidentiality.
consider three-party scenarios.
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1.1.6 Question as to why SNMP did not rate the same as for item
1.1.5? The evaluation is based on what was contained in the
submission documents, rather than capabilities of the protocol
itself. Too much hand waving.
1.1.7 No comments.
1.1.8 Question as to meaning of "reliable"? Discussion of transport
protocols was deferred to later in the meeting.
1.1.9 No comments.
1.1.10 SNMP received "P" because of hand waving in the submission
documents.
1.1.11 SNMP received "F" because this section of the submission
document indicated "t.b.d.". Diameter was the only protocol
submission to completely address this item.
1.1.12 We treated this requirement as "non-repudiation". There is a
concern that digital signatures are computationally expensive and are
not globally available. COPS has more work to do on this item.
1.1.13 Question that "no shared secrets" should be interpreted to
mean that an alternative key management mechanism is available? We
treated this as meaning that application-layer security could be
turned off in deference to transport layer security. There had been
discussion of the use of IKE in the AAA protocol.
1.1.14 No comments.
1.2.1 No comments.
1.2.2 No comments.
1.2.3 No comments.
1.2.4 Is there a need for a clear-text "password" for service such as
OTP, SecurID, et. al.? It was noted that all plain passwords are
exposed in clear-text at the NAS or other edge device, which is no
more inherently trustworthy than any AAA server or proxy.
1.2.5 We distinguished event-driven reauthentication from timer-
driven (or lifetime-driven). How is this requirement to be met in a
proxy environment?
1.2.6 We asserted that this requirement is an oxymoron.
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1.3.1 We had difficulty in determining what "static" meant, and from
which reference point it was measured.
1.3.2 We agreed that NAIs could be handled, possibly with some
restrictions.
1.3.3 No comment.
1.3.4 The SNMP submission documents contained significant hand
waving.
1.3.5 Similar comments as to item 1.2.5. The question was raised as
to how the server knows when to send this request?
1.3.6 We found that the notation in Diameter was weak, and of a least
common denominator nature. In general, there was concern about
achieving interoperability when the syntax was standardized but the
semantics were not. This area needs further work.
1.3.7 Question as to how this requirement is achieved via proxies?
1.4.1 No comment.
1.4.2 No comment.
1.4.3 No comment.
1.4.4 There was significant skepticism regarding batch accounting as
part of the AAA protocol. How large are the "batches"? Should this
requirement be met using FTP or something similar?
1.4.5 No comment.
1.4.6 No comment.
1.4.7 No comment.
1.5.1 No comment.
1.5.2 There was some discussion of what constitutes firewall
friendly. It was suggested that the firewall didn't want to look
into packets much past the application protocol address (e.g. UDP or
TCP port number). Protocols such as SNMP and COPS that have usage
other than AAA are at a disadvantage, since the firewall must look
deep into the application PDU to determine the intended purpose of
the packet. Diameter suffers from reliance of SCTP, which is not
widely deployed or widely recognized by firewalls. Should firewalls
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also be AAA proxy engines? Has this issue anything to do with
interoperability with NAT?
1.5.3 We had some confusion as to what the requirement actually was.
Raj seemed to be able to explain it, but the rest of us had to take
it on faith.
A poll was taken on overall acceptability and effort for each of the
protocols submitted, for requirements conformance.
Each member indicated their evaluation in the form of (Acceptable,
Not-Acceptable) with qualifiers for (Accounting, or effort to change)
This information will be summarized in the final report.
A general wrap-up discussion was held.
It was considered important that as much of the thought processes and
rationales be placed in the final report as is feasible. Mike St.
John will work with Dave Mitton on the ID. We really need to meet
the IETF July 14 submission deadline, even if we have to issue an
update on the AAA WG mailing list. All agreed that the process went
fairly well. In future evaluations of this nature, it would be well
for the evaluators to follow the requirements documents closely, for
the submitters to create accurate and complete conformance documents,
and to allow a "re-spin" cycle to correct errors and omissions in the
requirements documents and conformance documents.
A discussion of the transport protocol was held.
The issue with transport is congestion control. There has been a
problem with streams-oriented applications over TCP. The IESG is
increasingly sensitive to this issue in new protocols. It was noted
that AAA was a transaction-oriented application. Other request-
response applications, such as DNS, seem to scale welt to Internet-
scale using simple application-level retries and UDP transport. TCP
has problems with head-of-line blocking, especially when multiple
sessions are using a single TCP connection. AAA typically will send
3 or 4 iterations and then indicate a failure to the upper layers.
It won't continue retransmissions in the face of congestion, like
TCP. It was noted that bulk data transfer may not best be
implemented in the AAA protocol. Concern was voiced that SCTP is not
a widely implemented protocol. AAA will implement congestion control
by limiting the number of outstanding requests. Some RADIUS
implementations send lots of traffic when they encounter
misconfigured shared secrets, but this is likely caused by a lack of
proper error recovery. Diameter, as currently drafted, relies on
SCTP. Can AAA run over UDP? The IESG didn't say "no"; their issue
is addressing congestion control.
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Full Copyright Statement
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