8-5. MSFC Redundancy with Configuration Synchronization

· In config-sync mode, both MSFCs are active at all times; all interfaces and routing processes are available and active on both modules.
· One MSFC is "designated" and maintains the master copies of startup and running configurations. The other is "nondesignated" and receives its configurations from the designated module.
· The nondesignated MSFC can be monitored through an EXEC session, but doesn't allow the configuration mode.
· Config-sync mode allows an immediate failover because both MSFCs are always active. All VLAN interfaces are up, and any configured routing protocols are active on both modules.
· For MLS, either of two redundant MSFC modules can be involved in setting up a flow cache entry. The PFC is aware of both RP modules.
· For CEF, only the designated MSFC downloads the FIB and adjacency table information to the other modules. The designated MSFC is the one that initializes first, in the lowest module slot position.
· HSRP should be used to provide a redundant gateway address on each VLAN. Both MSFCs share a common gateway address, while operating their own unique interface addresses. (See section "8-6: Router Redundancy with HSRP" for more information about HSRP.)
· After config-sync mode has been enabled and is active, any configuration changes that are made on the designated MSFC are automatically synchronized with the nondesignated module:
- Whenever you enter the write mem or copy source startup-config commands, the startup configuration is updated across MSFCs.
- Whenever you enter the copy source running-config command, the running configuration is updated across MSFCs.
- As you enter commands in configuration mode, they are also sent to and executed on the nondesignated MSFC.