Core Issue
The Catalyst 6500 and 6000 series switches use the Supervisor Engine for Layer 2 (L2) switching and the Multilayer Switch Feature Card (MSFC), which is a daughter card, on the Supervisor Engine for Layer 3 (L3) routing functionality. The switch allows the user to install two Supervisor Engines on the same chassis in slot 1 and slot 2 for L2 redundancy. When the dual supervisor engines have the MSFC, they can be configured to provide L3 redundancy as well.
Hot Standby Router Protocol (HSRP) provides redundancy for IP networks, ensuring that user traffic immediately and transparently recovers from first hop router failures. HSRP allows multiple routers on a single LAN to share a virtual IP and MAC address, which is configured as the default gateway on the hosts. From the group of routers configured in a HSRP group, the one with the highest priority functions as the active router and the one with the second highest priority functions as the standby router. The active router assumes the role of forwarding packets sent to the virtual IP address. If the active router fails, the standby takes over as the new active router.
Resolution
These are the different types of configurations available for MSFC redundancy on a single Catalyst 6500 and 6000 chassis operating in hybrid mode. This runs Catalyst OS (CatOS) on the Supervisor and Cisco IOS Software on the MSFC:
- Dual router mode redundancy makes use of HSRP. Both the MSFCs can be active at the same time and establish routing protocol peer relationships with other routers. If one MSFC fails, the other MSFC takes over using the HSRP mechanism. This method can also be used to provide load sharing of VLAN traffic by using a single chassis.
- In single router mode redundancy, only one of the MSFCs is active and it establishes routing protocol peer relationships with other routers. The other MSFC takes over if the active MSFC fails. This method cannot provide load sharing capability using a single chassis.
Apart from the redundancy options available for MSFC on the same chassis, HSRP can also be used to provide MSFC redundancy and load sharing. This occurs when HSRP is available on Supervisors on a multiple chassis, just like a normal router-based network.
Certain requirements must be met for single chassis MSFC redundancy. Both the MSFCs must have identical configuration, except for HSRP and other network layer parameters like IP and Internetwork Packet Exchange (IPX) addresses, which have to be unique. This condition is due to the concept of designated MSFC, which programs the ASIC on the active Supervisor Engine for forwarding traffic. The designated MSFC is the one that comes up first (or has been up the longest), and it can either be the one in slot 1 or slot 2.
To resolve this issue, perform these steps:
- Before configuring HSRP for dual router mode redundancy, identify the active and standby MSFCs for each VLAN. All the HSRP commands are configured under the Switched Virtual Interfaces (SVIs) for the VLAN on both the MSFCs. The SVI acts as the routed interface for a VLAN.
- To access both the MSFCs from the Supervisor module, issue the session and session 16 commands.
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3. To configure the virtual IP address for the group, issue the standby [group-number] ip [ip-address] command.
4. Use the same group number and virtual IP address on both the MSFCs for the specific VLAN.
5. To configure the priority, issue the standby [group-number] priority priority command.
6. Select the active and standby MSFC for that VLAN.
If necessary, configure the standby [group-number] preempt command to always force the MSFC with the highest HSRP priority to be elected as the active MSFC for that VLAN.
For more information on MSFC redundancy and HSRP configuration, refer to these documents:
