[nsp] HSRP and VLANs

[Ed Ravin]

On Tue, Dec 16, 2003 at 09:17:57AM -0500, jlewis at lewis.org wrote:
> On Tue, 16 Dec 2003, Marco Matarazzo wrote:
> > > As I understand it, you need at least 3 IPs to do HSRP for one subnet
> > > or VLAN.  One IP for each physical interface on the router and one
> > > virtual IP which becomes the host's default gateway.
...
> I haven't tried this, but what if you put the real IPs in a different 
> subnet (maybe even RFC1918 IPs) and the standby IP in the customer's 
> subnet?

It might work, but you will need to set up routing for the real IPs,
since routing table entries will not be automatically created as they
are with interface addresses.

> Is there a limit (other than the number of VLANs a router can support) on 
> the number of standby IPs that can be configured?

Yes, my unscientific experimentation last year with the command line
showed that there can't be more than 255 HSRP definitions on a router.
I imagine the actual limits, if they are lower, are written up somewhere
in Cisco's documentation.  I've only got 23 on my 7200 with IOS 12.2.17,
so I haven't pushed this yet.