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Catalyst 3750 Switch Software Configuration Guide
OL-8550-09
Chapter 42 Configuring HSRP
Configuring HSRP
Enabling HSRP Support for ICMP Redirect Messages
The Internet Control Message Protocol (ICMP) is a network layer Internet protocol that provides
message packets to report errors and other information relevant to IP processing. ICMP provides
diagnostic functions, such as sending and directing error packets to the host.
When the switch is running HSRP, make sure hosts do not discover the interface (or real) MAC addresses
of routers in the HSRP group. If a host is redirected by ICMP to the real MAC address of a router and
that router later fails, packets from the host will be lost.
The Internet Control Message Protocol (ICMP) is a network layer Internet protocol that provides
message packets to report errors and other information relevant to IP processing. ICMP provides
diagnostic functions, such as sending and directing error packets to the host.
In releases earlier than Cisco IOS Release 12.2(18)SE, ICMP redirect messages were automatically
disabled on interfaces configured with HSRP. In Cisco IOS Release 12.2(18)SE and later, ICMP redirect
messages are automatically enabled on interfaces configured with HSRP. This feature filters outgoing
ICMP redirect messages through HSRP, in which the next hop IP address might be changed to an HSRP
virtual IP address. For more information, see the Cisco IOS IP Configuration Guide, Release 12.2.
Configuring HSRP Groups and Clustering
When a device is participating in an HSRP standby routing and clustering is enabled, you can use the
same standby group for command switch redundancy and HSRP redundancy. Use the cluster
standby-group HSRP-group-name [routing-redundancy] global configuration command to enable the
same HSRP standby group to be used for command switch and routing redundancy. If you create a cluster
with the same HSRP standby group name without entering the routing-redundancy keyword, HSRP
standby routing is disabled for the group.
This example shows how to bind standby group my_hsrp to the cluster and enable the same HSRP group
to be used for command switch redundancy and router redundancy. The command can only be executed
on the cluster command switch. If the standby group name or number does not exist, or if the switch is
a cluster member switch, an error message appears.
Switch# configure terminal
Switch(config)# cluster standby-group my_hsrp routing-redundancy
Switch(config)# end