[c-nsp] Catalyst with HSRP

[Jon Lewis]

On Tue, 17 Jul 2007, Tom Zingale (tomz) wrote:

> The 3560e/3750e, we can support up to 32 groups but each group can be
> supported across multiple vlans. Therefore, you can have one group on
> multiple VLAN's but it will only count once toward the 32 group limit.

Q. What is the implication of the use of the same HSRP group ID on 
multiple interfaces?

     A. When you define the same HSRP group ID on multiple interfaces, they 
all share the same HSRP virtual MAC address. In most modern LAN switches, 
there are no issues because they maintain a per-VLAN MAC address table. 
However, if your network contains any third party switches which maintain 
a system-wide MAC address table regardless of VLAN, you may experience 
problems.

Is it safe to assume the same question and answer apply for VRRP as well, 
and that SVI's for VLANs trunked over the same physical interface count as 
"multiple interfaces" in reference to the above Q&A?  So given a network 
of reasonably modern cisco gear, there's no compelling reason to use 
different HSRP or VRRP group numbers on any number of SVIs unless you need 
to support multiple groups within a single SVI / vlan subinterface?

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