[c-nsp] C7200-I/O-GE+E and HSRP group limits

Jon Lewis jlewis at lewis.org
Tue Mar 22 18:59:46 EST 2005

On Tue, 22 Mar 2005, Christopher E. Brown wrote:

> Of note, standby group number is used to autogen the roving MAC used by
> the interface, but you can re-use groupe numbers.
> IE, dot1q subinterfaces for vlans 2-22 could *all* used standby group
> 10, meaning all roving MACs used by HSRP are the same, but as they are
> in different VLANs...

I think you can only reuse group numbers across different interfaces.  At
least on the platforms I've messed with, dot1q or ISL subinterfaces of a
single physical interface must have unique hsrp group IDs.

> The use BIA is only required for older goofy platforms...  It has the
> nasty side effect of changing the root interface MAC of the routers
> during handoff.  (Imagine OSPF speaking subnet with a HSRP supported
> default for a couple non OSPF speakers, bang traffic loss...)

A workaround I used for this (only supported on some platforms) is to
configure the HSRP MAC address yourself, and make it the same for all
vlans/subinterfaces on a given physical interface...and the same on all
the other hsrp member routers.

 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

More information about the cisco-nsp mailing list