Have 1 Set of networks route differently then rest of the networks

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Apr 30th, 2008
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Greetings,

I have a customer that has 2 sites. 1 connection via broadband wireless (latency, drops packets...etc) and another via an MPLS connection. For the scope of this question I won't get into the technicalities of why we have routing the way we do, but there are other circumstances.


We will implement eigrp and iBGP on both sites with dual redistribution. By default all networks will route properly with the default metrics/weights - which is via the broadband wireless connection since it is higher bandwidth and there are less hops...etc


However, the customer desires their voice network to/from the building use the MPLS connections due to it being better link quality.


That's where my problem comes in since I'm having problems getting voice traffic to prefer another route - a standard route map won't work with it chosing X ip address or interface as the next hop since it would not allow redundancy/failover. I'd like to change the EIGRP metric (EIGRP is working due to a GRE tunnel over the MPLS network) just for the voice networks over the MPLS network.


Any suggestions or tips on this matter will be appreciated. I know this should be possible, but dang it has me stumped at the moment.

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Jon Marshall Thu, 05/01/2008 - 01:12
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From Cisco doc



"The set ip next-hop command verifies the existence of the next hop specified, and…


if the next hop exists in the routing table, then the command policy routes the packet to the next hop.


if the next hop does not exist in the routing table, the command uses the normal routing table to forward the packet."



So if you use a next hop ip address and then that ip address becomes unavailable then the voice traffic will get routed according to the normal routing table, which if i understand correctly is what you want.


You can also specify multiple ip next hop addresses in your route-map and it tries them in the order specified.


Jon

patrickjgalligan Sat, 05/03/2008 - 06:27
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What Jon has described is policy routing, which you may or may not want to do.


You can manipulate the Administrative Distance of selected routes to achieve what you want. Under your EIGRP routing process:

distance


is the AD you wish to set for these routes

is the address of the router you are learning these routes from

is the wildcard mask, to match the route source, will be 0.0.0.0 if you are matching just the one address for

is an access list matching the routes for which you wish to change the AD


So:

distance 220 192.168.1.1 0.0.0.0 1

sets the AD to 220 for all routes matched by access list 1 received from 192.168.1.1


If you want to make the iBGP routes preferred, you set the AD higher than 200.


Hope this helps.

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