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EIGRP / OSPF priority

I've got a problem with the distribution of a route in an environment using both EIGRP & OSPF.

I have a pair of 6509 switches (one core and the other distribution/access). On the core side of the network I have a 2600 router that's configured with OSPF area 0 (as is the core switch). I have a need to be able to occasionally migrate one of the remote WAN subnets over to the distribution side of the LAN (I won't go into too much detail, but it's basically down to the size of the site and availability of patch points into the core). At present my dist & core switches exchange routing information via EIGRP and what I'd hoped to do was create a vlan interface on the dist switch and then activate it when required. I'd hoped that this would propogate the route via EIGRP, but it seems that the OSPF routing from the 2600 is taking priority.

If I look at the routing table on the dist switch, it sees the vlan in question as directly connected, but the core switch shows a route obtained via OSPF from the 2600. I enabled 'debug eigrp transmit' on my dist switch and can see it sending the route updates as I activate and de-activate the interface...

Ideally what I'd like to happen is when I perform a no shut on the dist vlan interface, the core prioritises the route obtained via EIGRP, but when I perform a shut on the interface, it switches back to the route obtained via OSPF.

I'd appreciate any comments.

Chris

Reply to
Can2002
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There is quite a lot to this.

More specific routes always beat less specific routes.

i.e.

192.168.1.0 255.255.255.128 via 1.1.1.1

is ALWAYS prefered over

192.168.1.0 255.255.255.0 via 2.2.2.2

If there are two routes of the same prefix length then the administrtive distance comes into play.

formatting link
There are further possible problems with redistribution.

If your network really is 3 devices then step one would be to switch to running only one routing protocol.

Presumably it isn't?

Reply to
anybody43

Cheers, in my case the two routes in question both had 20 bit masks, but thanks for the confirmation.

Good point, I condensed the network down to avoid confusion, but I got to the bottom of the problem - my understanding of the 'network a.b.c.d' command. I had thought it meant 'propogate to these subnets' rather than 'propogate subnets of this prefix'... In my case I had the line 'network 10.0.0.0' in my eigrp config, but the network I wanted to propogate was 172.16.x.y! Once I added 'network 172.16.0.0' to the eigrp config it fixed it!

This bit that threw me was when I looked at the debug eigrp transmit output prior to this change, it appeared to be sending out updates for the 172.16.x.y network when I brought the relevant interface up and down, but it clearly wasn't!

Thanks for the feedback anyway, Chris

Reply to
Can2002

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