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Table Of Contents
About the SCE-Sniffer DHCP LEG
Information About the SCE-Sniffer DHCP LEG
SCE-Sniffer DHCP LEG Operation
Information About SCE-Sniffer DHCP LEG Functionality
DHCP Initial Logon Transaction
DHCP Lease Extension Transaction
About the SCE-Sniffer DHCP LEG
This module describes the Subscriber Manager SCE-Sniffer DHCP LEG software module and the terms and concepts relevant to the SCE-Sniffer DHCP LEG.
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Information About the SCE-Sniffer DHCP LEG
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Information About the SCE-Sniffer DHCP LEG
The SCMS SM SCE-Sniffer DHCP LEG is a software module that receives RDR (Raw Data Record) messages containing DHCP information from SCE devices configured with a DHCP sniffer service. The SCE-Sniffer DHCP LEG is an extension of the Subscriber Manager (SM) software and runs as part of the SM.
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SCE-Sniffer DHCP LEG Operation
The SCE device analyzes DHCP traffic, and reports the DHCP transactions to the SM device using the RDR protocol. The SM extracts the modem MAC address, the CPE IP address, and optionally, the subscriber package information from the RDR, and triggers a logon or logout operation to the SM.
The following diagram represents the operation of the SCE-Sniffer DHCP LEG:
Figure 1-1 SCE-Sniffer DHCP LEG Operation
Terms and Concepts
The following is a list of terms and concepts that are necessary to understand the SCE-Sniffer DHCP LEG and SM configuration and operation. Additional information regarding the various issues can be found in the Cisco SCMS Subscriber Manager User Guide .
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LEG (Login Event Generator)
A software component that performs subscriber login and logout operations on the SM, which is used to handle dynamic subscriber integration.
RDR (Raw Data Record)
A client/server data protocol that enables the SCE devices to export reports about network transactions to external collectors. This is a Cisco proprietary protocol.
Cable/Satellite Modem
A data modem that provides Internet access over cable and satellite networks. The modem usually corresponds to a single subscriber of the Internet Service Provider (ISP).
CPE (Customer Premise Equipment)
Any equipment that an end-user can connect to the network through a modem. The end-user usually owns multiple CPE devices that are used to connect to the Internet through a single modem.
DHCP ACK Packet
The final packet that is transmitted from the DHCP server in each DHCP transaction (except the release transaction). After the transmission of the DHCP ACK packet, the results of the transaction are final.
DHCP Lease Extension Transaction (Renewal)
A DHCP transaction for renewal of the entity lease time. When the lease time has been reached, the network entity is removed from the network. The LEG uses this query to logon the subscriber using the new lease time.
DHCP Release Transaction
A DHCP transaction for releasing IP addresses. This transaction is used to logout network entities from the network. The DHCP release transaction is rarely used. Logout is usually performed when the lease time expires, and not directly with a release transaction. The LEG uses the release query to logout a subscriber from the SM.
DHCP Sniffer
The software logic inside the SCE device that analyzes DHCP traffic and sends the information to the SCE-Sniffer DHCP LEG using the RDR protocol.
Subscriber Mappings
The SCE platform requires mappings between the network IDs (IP addresses) of the flows it encounters and the subscriber IDs. The SM database contains the network IDs that map to the subscriber IDs. The SCE network-ID-to-subscriber mappings are constantly updated from the SM database.
The main function of the SCE-Sniffer DHCP LEG is to provide the SM with network-ID-to-subscriber mappings in real time.
Subscriber Domain
The SM provides the option of partitioning SCE platforms and subscribers into subscriber domains. A subscriber domain is a group of SCE platforms that share a group of subscribers. Subscriber domains can be configured using the SM configuration file and can be viewed using the SM Command-Line Utility (CLU).
For additional information about domains and domain aliases, see the "Configuration File Options" section in the Cisco SCMS Subscriber Manager User Guide .
Subscriber Package
The policy enforced by Cisco solutions on a certain subscriber is usually defined by a policy subscriber package. The SCE-Sniffer DHCP LEG can handle the package ID in any of the following ways:
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For additional information, see Configuring Policy Association and the Cisco Service Control Application for Broadband User Guide .
Information About SCE-Sniffer DHCP LEG Functionality
The SCE devices analyze the DHCP ACK packets of DHCP transactions and send the information to the SCE-Sniffer DHCP LEG that resides on the SM. The LEG performs login and logout operations to the SM using the information sent from the SCE devices. The DHCP transactions that are relevant for the operation of the LEG are initial logon , lease extension , and release .
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DHCP Initial Logon Transaction
The following is a detailed description of the attributes extracted from the DHCP initial logon transaction:
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For cable environments—The subscriber ID is the modem MAC address, which you extract from option 82 (Remote-ID sub-option of the DHCP Relay Agent Information Option). Therefore, for a successful logon operation, it is required that option 82 contains the modem MAC address in the DHCP initial logon transaction. If option 82 is missing, it is not possible to perform a logon operation. Furthermore, the value of option 82 is compared with the haddr field to identify modem transactions and not login the modem IP address to the SM.
For non-cable DHCP environments—The LEG supports using other DHCP options for the subscriber ID. If the DHCP option does not exist in the packet, it is possible to use the IP address as a fallback. In this case, the subscriber ID is in the format IP_a.b.c.d.
The chain of decisions regarding the subscriber-ID is as follows:
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Each subscriber might have multiple IP addresses, depending on the number of CPE devices connected to the modem. A logon operation is triggered for each assigned IP address in the DHCP message.
If the transaction correlates to a CPE device, the assigned IP address for that CPE device is added to the SM database. The IP address of the modem is not added to the SM database. If the transaction correlates to a modem device, no IP mappings are added to the SM database, but a logon operation is performed anyway to update package information.
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If the transaction correlates to a CPE device, the assigned IP is added to the SM database with a lease time taken from option 51 (lease time option). Note that option 51 must contain the lease time; otherwise no logon operation is performed.
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The policy information is assigned according to configurable options in the DHCP message. The LEG includes a component that converts the package information data from the DHCP packet to a subscriber package ID. If the packet does not contain package information, it is possible to log in the subscriber with a default package, or log in the subscriber with no package information at all.
After extracting the above information, the LEG performs a logon operation to the SM.
DHCP Lease Extension Transaction
The same attributes are extracted from the DHCP lease extension transaction as for the DHCP initial logon transaction, but the existence of option 82 is not required. If the modem MAC address cannot be retrieved from option 82, the SM database is queried for this information.
DHCP Release Transaction
The DHCP release transaction is handled differently to the other DHCP transactions. If the transaction correlates to a CPE device, the LEG performs an SM logout operation with the IP address of the CPE, which appears as a released IP address in the packet itself.
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Posted: Tue Jan 22 17:09:18 PST 2008
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