[c-nsp] HSRP and RIPv2

[Bruce Pinsky]

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Crist Clark wrote:
> Bruce Pinsky wrote:
> 
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>> Crist Clark wrote:
>>
>>> We have a network with some devices that only speak RIPv2. On the Cisco
>>> routers connected to the network, we are redistributing routes from
>>> EIGRP
>>> into RIP. Two routers are in an HSRP group. What we see happening is
>>> each of the routers is announcing the networks using RIP, but each is
>>> sending the updates with a source address of their interface on the
>>> network
>>> and all zeros for the next hop. Therefore the other RIP listeners use
>>> the source on the announcement as the next hop. What we want is the
>>> other RIP listeners to have the HSRP address as the next hop.
>>>
>>> I am not aware of a way to get the routers to use the HSRP address as
>>> the source on their route announcements. That does not mean there is
>>> not one. Is there? Another option is to use "set next-hop" to force the
>>> next hop in the RIP advertisements to be the HSRP address, but that
>>> becomes a slight administrative hassle since this configuration is
>>> repeated at multiple sites and we want to keep the site-specific
>>> configuration to a minimum. It would be nice to just be able to tell the
>>> router to use the HSRP address as the next hop and not specify the IP
>>> address explicitly. Finally, another option might be to simply shut up
>>> the router that is in stand-by, but how do we tell it to automatically
>>> start talking RIP again when it comes on line?
>>>
>>> This would seem to be something many have had to deal with before, HSRP
>>> routers advertising their "real" IPs rather than the HSRP address into
>>> RIP. Any suggestions?
>>
>>
>>
>> You're using a routing protocol.  The RIPv2 listeners hear both of the
>> adverts.  What is the problem?   Even if one of the advertising routers
>> dies, the other will be sending updates.
> 
> 
> Both routers advertise the same metric for the routes in RIP. The routers
> could chose either router. However, we'd actually prefer the HSRP primary
> to be the one used when both are up. So, should we play with the next hop?
> Or play with metrics? Both seem pretty ugly with possible hidden problems.
> 


You should be able to either 1) set the metric as part of the
redistribution from EIGRP; or 2) use an offset-list for RIP to add
"distance" to the backup route.

The point here is that a dynamic routing protocol provides next-hop info
for non-local destinations.  If you could/did force the next-hop in the RIP
adverts to the HSRP address, then you may as well just get rid of RIP
altogether and simply rely on a statically configured default gateway on
all the devices and tweak HSRP priority to achieve what you want.

In fact, that's the least complex and most safe way to get the desired
effect.  As I'm fond of saying, it's better to eliminate operational
complexity wherever possible.

- --
=========
bep

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