About the CNR LEG
This module describes the Subscriber Manager CNR LEG software module.
The Cisco Network Registrar (CNR) Login Event Generator (LEG) is a software module that forwards login and logout events from the CNR to the Cisco Service Control Management Suite Subscriber Manager (SCMS SM). The CNR LEG is actually a CNR extension developed in C++. The extension points used by CNR LEG are:
About the CNR LEG Module
The CNR LEG module requires the use of option 82 sub-option 2 (Relay-Agent-Information Option with the Remote-Id sub-option), which contains the CM-MAC, in all DHCP requests. If option 82 does not exist in a renewal transaction, an attempt to extend the lease based solely on the IP address is performed. This will succeed only if the IP address was previously logged in to the Subscriber Manager (SM) by the LEG, in the event of a full DHCP transaction, or via other interfaces to the SM.
The CNR LEG protects the SM and the connection to the SM from any DHCP Denial of Service (DoS) attacks, which are performed on the CNR. To reduce the login rate to the SM, the LEG ignores identical DHCP requests that are approved by the CNR. The requests are sent to the CNR in short time intervals.
For additional information about extending the CNR functionality using extension points, see the CNR CLI Reference Guide.
The CNR LEG was carefully developed and thoroughly tested on Solaris and Windows platforms for both functional correctness and robustness. It does not jeopardize the stability or the reliability of the CNR.