HSRP Issue

Unanswered Question
May 16th, 2009

Hi,

we are confiured HSRP between the two router on our LAN Side

my issue is i have two interface on my both the router for example

Router A Router B

fa0/0 Fa0/0

10.80.11.2 10.80.11.3

standby 1 10.80.11.1

Router A Router B

fa0/1 Fa0/1

10.90.11.2 10.90.11.3

standby 1 10.90.11.1

Iam configuring both the interface on the single HSRP group

My worry is whether i need to configure both the interface on the single HSRP group or Different group

if different may i know the reason for that

Thanks in advance

I have this problem too.
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Giuseppe Larosa Sat, 05/16/2009 - 11:15

Hello Vinoth,

on routers you need to use different HSRP groups when used on subinterfaces of the same physical interface.

In your case you have two different interfaces fas0/0 and fas0/1 on each router so there is no possible ambiguity on what interface should process a received hello: lan switch(es) will forward the hello on a per vlan basis.

So if the two interfaces of each routers are connected to access ports in two different vlans everything is well.

Using two different group numbers provide you:

a more clean config using different groups can make troubleshooting easier

and what is more important it provides protection from possible events that would cause the two vlans to merge (by accident or fault of any type).

For the same reasons it is better to use different HSRP MD5 passwords on each group.

This is important on multilayer switches also on powerful 6500 they can experience 100% cpu if they start to compete for HSRP.

We had an issue caused by a config error that merged two different vlans using the same HSRP group number.

So you can do so but I would use two different numbers for all the reasons above.

Hope to help

Giuseppe

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