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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 23 Configuring Redundancy
MSFC Redundancy
Failure Case 3: Active Sup #1 Fails
This sequence occurs when the active supervisor engine (Sup #1) fails:
1.
Because the Layer 3 state is maintained, the MLS entries of MSFC #1 gracefully age out of the
Sup #2 Layer 3 cache while MSFC #2 takes temporary ownership of these MLS entries using its
XTAG value.
2.
The standby supervisor engine maintains the Layer 2 state so that there is no Layer 2 convergence
time.
3.
MSFC #2 removes all the dynamic and reflexive ACLs that are programmed in the hardware by
MSFC #1.
4.
MSFC #2 reprograms the static ACLs in the Sup #2 ACL ASIC. MSFC #2 is now the designated
MSFC.
Failure Case 4: Standby Sup #2 Fails
This sequence occurs when the standby supervisor engine (Sup #2) fails:
1.
The MLS entries for MSFC #2 gracefully age out of the Sup #1 Layer 3 cache while MSFC #1 takes
temporary ownership of these MLS entries using its XTAG value.
2.
The MLS entries from MSFC #1 are not affected.
3.
MSFC #1 removes all the dynamic and reflexive ACLs that are programmed in the hardware by
MSFC #2. MSFC #1 remains the designated MSFC.
Failure Case 5: New or Previously Failed Supervisor Comes Back Online
This sequence occurs when the previously failed supervisor engine (Sup #2) comes online:
1.
Sup #1 continues to be the active supervisor engine.
2.
Sup #2 synchronizes its image and configuration with Sup #1 (unless high-availability versioning is
enabled).
3.
MSFC #2 (on Sup #2) comes up. If the HSRP preempt for VLAN 21 is configured, then MSFC #2
becomes HSRP active. The MLS entries for MSFC #1 are purged and then relearned through
MSFC #2.
4.
MSFC #1 remains the designated MSFC for the static ACLs.
Configuring Redundancy with HSRP
Although the supervisor engine software high-availability feature maintains the protocol state between
the redundant supervisor engines, you need to configure HSRP for failover between the redundant
MSFCs. HSRP is used to provide first-hop, unicast redundancy. You can configure one or more HSRP
groups on the MSFC VLAN interfaces to provide automatic routing backup for your network. Each
VLAN interface in an HSRP group shares a virtual IP address and MAC address. You can configure the
end stations and the other devices to use the HSRP address as the default gateway so that if one router
interface fails, the service is not interrupted to those devices.
The interface with the highest HSRP priority is the active interface for that HSRP group.