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Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 22 Configuring Redundancy
MSFC Redundancy
Figure 22-3 Dual MSFC Operational Model for Redundancy and Load Sharing—
VLANs 10, 12, 21, and 23
Only the active HSRP router for a VLAN will respond with the HSRP MAC address for ARP requests
to the HSRP IP address. The active HSRP router will in turn ARP for the end stations’ MAC address and
populate its ARP cache. By using both MSFCs in a single chassis to share HSRP duties for even VLANs,
you can share the control plane ARP traffic. In an MSFC failure, only the ARP entries on the affected
VLAN would need to be relearned.
The tradeoff for this level of redundancy and load sharing is the added complexity of keeping track of
the even and odd VLANs on the MSFCs within a Catalyst 6000 family switch chassis.
MLS entries are created for packets arriving at the HSRP MAC addresses as well as those arriving with
the router’s real MAC addresses. HSRP is used for unicast traffic first-hop redundancy; for traffic
received through another router attached to VLAN 10, for example, the actual MAC address of
Sup #1/MSFC #1 is used.
Understanding Failure Scenarios
The five examples in this section describe possible failure scenarios within a single chassis with dual
supervisor engines and dual MSFCs (see
Figure 22-4
) when you enable high availability. The designated
MSFC refers to the MSFC that is used to program the ACL ASIC for static ACLs.
VLAN 10/21
VLAN 12/23
Trunk 1
Trunk 2
Switch S1
Switch S2
Slot 1
Sup#1/MSFC#1
HSRP Active VLAN 10: priority 110
HSRP Standby VLAN 21: priority 108
HSRP Standby VLAN 12: priority 109
HSRP Standby VLAN 23: priority 107
Slot 2
Sup#2/MSFC#2
HSRP Standby VLAN 10: priority 109
HSRP Standby VLAN 21: priority 107
HSRP Active VLAN 12: priority 110
HSRP Standby VLAN 23: priority 108
Slot 1
Sup#1/MSFC#1
HSRP Standby VLAN 10: priority 108
HSRP Active VLAN 21: priority 110
HSRP Standby VLAN 12: priority 107
HSRP Standby VLAN 23: priority 109
Slot 2
Sup#2/MSFC#2
HSRP Standby VLAN 10: priority 107
HSRP Standby VLAN 21: priority 109
HSRP Standby VLAN 12: priority 108
HSRP Active VLAN 23: priority 110
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