Configuring the SCE-Sniffer DHCP LEG

The SCE-Sniffer DHCP LEG is configured using two configuration files, dhcpsnif.cfg and dhcp_pkg.cfg , which reside in the sm-inst-dir /sm/server/root/config directory ( sm-inst-dir refers to the SM installation directory).

The configuration files consist of sections headed by a bracketed section title; for example, [RDR Server]. Each section consists of several parameters having the format parameter=value. The number sign ("#") at the beginning of a line signifies that it is a remark line.

The general configuration of the SCE-Sniffer DHCP LEG resides in dhcpsnif.cfg. The dynamic package association configuration resides in dhcp_pkg.cfg.

Configuring the General Settings

The following is a description of the configuration variables of dhcpsnif.cfg.

To extract and handle the DHCP messages received by the RDR server, this parameter must be set to yes.

Possible values for this parameter are trueand false. The default value is true.

Defines whether the SM should add all messages, including successful logins and logouts, to the user log.

Possible values for this parameter are trueand false. The default value is false.

Defines whether all login operations should use the default domain "subscribers".

Possible values for this parameter are trueand false. The default value is true.

If the value is set to false, the SM will log in the subscribers using the domain name identical to the IP address of the SCE that received the DHCP traffic for that subscriber. In this case, you will have to configure domain aliases as described in Cisco SCMS Subscriber Manager User Guide .

Indicates whether to check if this is a cable modem transaction; i.e., compare the value of the Remote-Id sub-option (option 82 sub-option 2) with the haddr DHCP header field. If it is a cable modem transaction, use only the policy information.

Possible values for this parameter are trueand false. The default value is true.

Possible values for this parameter are any combination of the following types: DHCPACK, DHCPRELEASE. The default value is set to DHCPACKand DHCPRELEASE.

Note For this LEG to work correctly, use the configuration file to enable the RDR server in the SM.

Defines which DHCP option to use for subscriber ID association. For DHCP options that have sub options, a colon separates the DHCP option and the sub option. The default value is Relay-Agent-Information using the Remote-Id information, i.e. 82:2.

Defines the format type of the DHCP option defined by the dhcp_option parameter above.

Possible values for this parameter are binaryor string. The default value is binary.

Defines the type of fallback that occurs when packet does not contain the configured DHCP option.

The possible value for this parameter is ipfor using the allocated IP to create a subscriber ID in the format IP_a.b.c.d. If this parameter is not set, no fallback occurs, and the login fails. The default is not set.

[SCE-Sniffer DHCP LEG] 
start=yes 
log_failures=true 
log_all=false 
use_default_domain=true 
is_cable=true 
[Sniffer] 
packet_types=DHCPACK 
[Subscriber ID] 
dhcp_option=82:2 
dhcp_option_type=binary 
default_id=ip

Configuring Policy Association

Subscriber policy configuration in the SCE-Sniffer DHCP LEG can be handled in any of the following ways:

Dynamic Assignment of Policy Information

Dynamic assignment of policy information is supported if the policy information is submitted in the DHCP packets. The LEG concatenates the desired options and creates a policy-name . It is possible to map, using the configuration, between the policy-names and the application policy parameters such as package IDs and Virtual-links. The SCE-Sniffer DHCP LEG can support multiple policies.

To extract the policy information data from the DHCP packet, use the dhcp_pkg.cfg configuration file to define the option types that contain the policy information and define the conversion map of the policy-names to the package IDs (or any other policy) of the Service Control Application for Broadband (SCA BB).

The LEG is able to add additional data to the login operation based on the LEG configuration. This data is added as a key-value pair. Other modules in the login chain can use this data, such as the SOAP LEG (see the Cisco SCMS SM SOAP LEG Reference Guide ). This data can be created by concatenating the data of several DHCP options and can be given a user-defined label.

Defines the DHCP options that contain the policy association information and defines the order of concatenation of the data. The DHCP header field called giaddr (Relay-Agent IP) is also supported; it requires the use of the type integer in the option_type parameter.

Defines the format type of the DHCP options and fields defined by the options_order_for_policy_name parameter.

Possible values for this parameter are binary(a binary string that is converted to an ASCII hexadecimal string), string(an ASCII string), or integer(a 4-byte integer converted to an IP address string in dotted notation). Order the list in the same way as options_order_for_policy_name.

Defines the separator character to use between two options when concatenating them to each other to create the policy name. Any character is accepted. The default value is '_'.

Determines whether to use a default policy when no policy information can be extracted from the DHCP data, such as the configurable options are missing or no options were configured.

Possible values for this parameter are trueor false. The default value is false.

Defines the default policy ID to use if no policy information is extracted from the DHCP data. This parameter is relevant only if the use_default parameter is set to true.

Possible values for this parameter are any integer number. This parameter has no default value.

Defines whether to perform a login without policy information when no policy information can be extracted from the DHCP data and the use_default parameter is set to false.

This parameter is relevant only if the use_default parameter is set to false.

Possible values for this parameter are trueor false. The default value is true.

Defines the name of the application property that contains the policy information. This parameter has no default value.

Defines whether to write detailed user-log messages for all policy association events.

Possible values for this parameter are trueor false. The default value is false.

Defines whether to write a user-log message for every assignment of the default value (as defined by the default_policy parameter).

Possible values for this parameter are trueor false. The default value is false.

Multiple entries containing the information to convert from the policy information as it appears in the DHCP packet to the policy property value to be used by the SCA BB application.

The [Additional Data] section of the configuration file contains the following parameters:

Possible values are the option number or, in the case of DHCP options with sub-options, the option and sub-option separated by a colon. For example, 43:123 or 61.

Defines the keys that should mark the DHCP options defined by the label_options parameter.

Defines the format type of the DHCP option defined by the label_options parameter.

Possible values for this parameter are binary(a binary string that is converted to an ASCII hexadecimal string) or string(an ASCII string).

Dynamic Assignment of Policy Information Example

Suppose that the policy information appears inside option 43 (Vendor Specific Option) of the DHCP packet and that both subtypes, 102 and 101, are in use. Configure the options_order_for_policy_name parameter as follows:

options_order_for_policy_name=43:102,43:101

Suppose that option 43 with subtype 102 contains the type of package (gold, silver, or bronze), and that option 43 with subtype 101 contains domain information (the package type has a different meaning in different domains). If the separator value is configured to the default value, configure the mapping_table entries as follows:

mapping_table.gold_domain1=11 
mapping_table.gold_domain2=12 
mapping_table.silver_domain1=13 
mapping_table.silver_domain2=14

This configuration means that if the DHCP packet contains the value 'gold' inside option 43 with subtype 102, and the value 'domain1' inside option 43 with subtype 101, the package ID that will be associated to the subscriber in the SM will have the value 11.

The following configuration describes how to add the data of the Relay-Agent Circuit-Id option as additional data to the login operation:

[Additional Data] 
label_options=82:1 
label_keys=PORT_ID 
label_option_type=string

[DHCP.Policy.Package] 
options_order_for_policy_name=43:102,43:101 
name_separator_value=_ 
use_default=true 
default_policy=1 
policy_property_name=packageId 
allow_login_with_no_policy=false 
log_all=false 
log_default_assignment=false 
mapping_table.gold_domain1=11 
mapping_table.gold_domain2=12 
mapping_table.silver_domain1=13 
mapping_table.silver_domain2=14 
[Additional Data] 
label_options=82:1 
label_keys=PORT_ID 
label_option_type=string

Static Assignment of Policy Information

If the installation does not require dynamic assignment of package information, the configuration file dhcp_pkg.cfg should define the default package ID to be assigned to all the subscribers, as shown in the following example:

[DHCP.Policy.Package] 
policy_property_name=packageId 
allow_login_with_no_policy=false 
use_default=true 
default_policy=1 
[DHCP.Policy.VirtualLinkDownstream] 
policy_property_name=downVlinkId 
allow_login_with_no_policy=false 
use_default=true 
default_policy=0 
[DHCP.Policy.VirtualLinkUpstream] 
policy_property_name=upVlinkId 
allow_login_with_no_policy=false 
use_default=true 
default_policy=0

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