8-4. MSFC Redundancy with Single Router Mode

Only the Catalyst 6000 supports redundant supervisor engines with redundant route processors (MSFC/MSFC2).
Only one MSFC is designated and active; the other is booted up, synchronizes its configuration with the active MSFC, starts any routing protocol processes, but keeps all interfaces in the "line down" state so that no network traffic is exchanged.
Only the designated and active MSFC is involved in creating MLS flow cache entries for the switching engine and in creating and downloading the CEF FIB and adjacency tables to the PFC2 switching engine.
In the event of a failure, single router mode (SRM) causes the nondesignated MSFC to bring its interfaces up and allow its routing protocols to converge. During this time, the existing Layer 3 switching information supplied by the failed MSFC continues to be used by the designated Supervisor PFC until the new MSFC can provide an update.
Both MSFC modules must run the same Cisco IOS Software imageSoftware Release 12.1(8a)E2 or later.
The Supervisor modules must run in high-availability mode to support SRM, using Supervisor Engine Software Release 6.3(1) or later.
Hot Standby Router Protocol (HSRP) is not necessary in SRM, because only one MSFC is active in the chassis at any one time. However, you should use HSRP if you have other MSFC or Layer 3 devices that have a presence on the same VLANs as the SRM MSFC. These other devices can then act as redundant gateways on those VLANs.