Wednesday, July 2, 2008

The Importance of HSRP groups

When using the standby command to setup HSRP, one optional parameter is to use a group number. When I configure it, I typically always use one, even though I never really had a good reason to do it.

One thing to keep in mind is dealing with the virtual MAC address HSRP uses. By default, this MAC address is 0000.0c07.ac00, if no group number is specified. If a group number is used, it is added to the last word. For example, group three becomes 0000.0c07.ac03. Further details here.

In general, you will usually only use one HSRP group per vlan, so this isn't a problem. But if you have another device spanning multiple vlans that needs to talk to multiple HSRP speakers simultaneously, this can create MAC address conflicts if the same HSRP groups are used.

1 comment:

Anonymous said...

This could be why my Netscaler is behaving strangely...