Cisco Cisco IOS Software Release 12.4(6)T

Increasingly, many hundreds of subinterfaces are being configured on the same physical interface, with 
each subinterface having its own HSRP group. The negotiation and maintenance of multiple HSRP 
groups can have a detrimental impact on network traffic and CPU utilization.

Only one HSRP group is required on a physical interface for the purposes of electing active and standby 
routers. This group is known as the ‘master’ group. Other HSRP groups may be created on each 
subinterface and linked to the master group via the group name. These linked HSRP groups are known 
as ‘client’ or ‘follow’ groups.

The HSRP group state of the client groups follows that of the master group. Client groups do not 
participate in any sort of router election mechanism. 

Client groups send periodic messages in order to refresh their virtual MAC addresses in switches and 
learning bridges. The refresh message may be sent at a much lower frequency compared with the 
protocol election messages sent by the master group.

Configuration information is included in the “Configuring HSRP” chapter in the Cisco IOS Application 
Services Configuration Guide, Release 12.4T, at the following URL:

Command reference information is included in the Cisco IOS IP Application Services Command 
Reference, Release 12.4T, at the following URL:

The following commands are new or modified for this feature:

An alphabetical list of all Cisco IOS Release 12.4T commands is in the Cisco IOS Master Command List, 
Release 12.4T, at the following URL