[c-nsp] HSRp and OSPF metrics

[Bruce Pinsky]

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Mark Kent wrote:
> I've got two 4948 L3 switches that have several
> netblocks split between them, using hsrp.
> 
> That is, under normal operating conditions switch A
> is the primary gateway for 192.168.1/24 and switch B is 
> primary gateway for 192.168.2/24.
> 
> Both switches use ospf to let the rest of my network
> know about these netblocks.
> 
> How can I get OSPF to either
> 
> a) redistribute only netblocks for which it is currently the
>    active HSRP box?
> 
> or
> 
> b) put a different metric on the redistributed routes depending
>    on whether the box is active or standby for a particular netblock?
> 

Well, you can't affect the advertising via OSPF based on HSRP currently.
So I ask....

First, why are you redist'ing instead of just sourcing in OSPF?

Second, since both switches should have interfaces in both subnets, you
should set the metrics on switch 1 interface to .1 subnet to be better than
switch 2's interface to .1 subnet and vice versa.  Now in steady state, you
will have both routes to both subnets from both routers but with one being
preferred over the other.  Then depending on the failure mode that causes
HSRP to failover, one router will stop advertising its routes.

There are some other games you could play with setting of metrics via
route-maps if you absolutely have to redistribute.  Also, depending on your
IOS version, you might be able to use EEM to do some config changes upon
notification of a change in standby address.

- --
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bep

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