Distributed default route.

Answered Question
Nov 29th, 2007

All of our routers are configured with a static default route that point to the IP address of the last hop router before our firewall. This has worked great in the past, but now we want to change the way default route is applied so that we don't have to config each router.

I will add a static default route at the last hop router and distribute it into EIGRP using a route-map and metrics. I've tested this and it works great.

In the past, on each router that had it's own static default route, when you typed in 'sho ip route' the gateway of last resort was the IP address in the default route statement. Now when the individual static entries on the routers are removed and the default route is presented to a router via EIGRP, when I do a 'show ip route' the gateway of last resort is the next-hop upstream router interface from which the EIGRP updates came from.

This presents the problem that you can't tell what the default route really is unless someone travelled hop by hop to the final source of the default route.

Is this the way it's supposed to work? Once we go to the distributed method of injecting default route, the actual default route is hidden on all other routers?

Correct Answer by Edison Ortiz about 9 years 2 months ago

That's the expected behavior.

With IGPs, the route will contain the device providing the path to the destination address as the next-hop.

Let's put it this way:

You have a router on 192.168.1.0/24 segment and it receives a default route with next hop 10.1.1.1 ?

How does 192.168.1.254 device knows how to get there ? It needs to use a device on its segment first, right ? Well, that's what the next-hop information provides.

The next hop should be in the same segment (192.168.1.1, for instance) and 192.168.1.1 would have another interface (10.1.1.254) providing that routing path.

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Correct Answer
Edison Ortiz Thu, 11/29/2007 - 09:36

That's the expected behavior.

With IGPs, the route will contain the device providing the path to the destination address as the next-hop.

Let's put it this way:

You have a router on 192.168.1.0/24 segment and it receives a default route with next hop 10.1.1.1 ?

How does 192.168.1.254 device knows how to get there ? It needs to use a device on its segment first, right ? Well, that's what the next-hop information provides.

The next hop should be in the same segment (192.168.1.1, for instance) and 192.168.1.1 would have another interface (10.1.1.254) providing that routing path.

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