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From: noc on 14 Dec 2009 17:56

Hi All:

It's cisco newbie here and I have a question about the best approach for
configuring HSRP v2.

The context of the question is that, overall, we anticipate having
about 20 vPCs and 3-400 VLANs. Each VLAN will be associated with two
or more vPCs, and we will use HSRP on all of the VLANs so as to
provide next hop redundancy.

The question is, should we use 1 HSRP group per VLAN, or should we
associate multiple VLANs for every HSRP group? Is there one approach
that would optimize the usage of system resources? Is there a limit on
how many VLANs can be included in a single HSRP group?

Thanks in advance for any information you can provide.

noc(a)ucalgary.ca
From: Stephen on 16 Dec 2009 17:16
On Mon, 14 Dec 2009 22:56:56 +0000 (UTC), noc <noc(a)ucalgary.ca> wrote:

>
>Hi All:
>
>It's cisco newbie here and I have a question about the best approach for
>configuring HSRP v2.
>
>The context of the question is that, overall, we anticipate having
>about 20 vPCs and 3-400 VLANs. Each VLAN will be associated with two
>or more vPCs, and we will use HSRP on all of the VLANs so as to
>provide next hop redundancy.
>
i have only used this with VLANs where they segregate subnets across
sets of switches - the main difference is that the topology of each
VLAN can be different depending on fibre faults etc.

>The question is, should we use 1 HSRP group per VLAN, or should we
>associate multiple VLANs for every HSRP group?

HSRP "context" is within 1 subnet, and AIUI you describe multiple
VLANs, 1 subnet per vlan. So i think you need 1 or more groups per
VLAN. You can re-use the group numbers in each VLAN.

400 VLANs for 20 vPCs does seem a bit backward, but the numbering
implies most of them are inactive or idle.....

Is there one approach
>that would optimize the usage of system resources?

Yes - only 1 VLAN :)

Seriously - if all the VLANs are routed together it may not make much
sense to complicate life with VLANs.

If you need them for say security segregation, then fine.

Is there a limit on
>how many VLANs can be included in a single HSRP group?
>
Never seen it done, so dont know - the acid test is try to configure
it.

What you may hit 1st is the number of HSRP instances or VLANs
supported on a box.

Note increasing these imply more IP routing / firewall interfaces or
VRFs, so you might hit a limit there 1st.

you can expect hardware limits on switches, but it varies by model
number. Switches often have a limit as well, although that may just be
a cisco "recommendation" (ie where you start to hurt performance, or
where cisco think you should spend more money for a faster box).

No substitute for hunting the manuals here, or a bench test if you
have the hardware.

>Thanks in advance for any information you can provide.
>
>noc(a)ucalgary.ca

Good luck
--
Regards

stephen_hope(a)xyzworld.com - replace xyz with ntl
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