[c-nsp] Running OSPF on PE-to-CE

[ar]

Hi. I actually dont need a sham-link. Because I want the backdoor or intra-area link to be utilized.

My only concern is that, I understand intra-area is prefered over the inter-area route when VPN routes are redistributed back to the ospf domain. This is the common setup.
But in my setup, its not an inter-area route. They are both E2 routes since vlans are redistributed to ospf. Then ospf redistributed to MP-BGP. Then MP-BGP redistribited back to OSPF.  My show ip route below shows the to routes: via the backdoor link and via the MPLS/VPN. Both E2 routes. I cant seem to understand yet what will be the route decision in this case. Two identical external routes on the routing table. But it seems, via the backdoor is being preferred even if I increase the metric.



________________________________
From: Enno Rey <erey at ernw.de>
To: ar <ar_djp at yahoo.com>
Cc: "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net>
Sent: Sunday, October 16, 2011 12:31 AM
Subject: Re: [c-nsp] Running OSPF on PE-to-CE

Hi,

this one might be helpful

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ospfshmk.html

thanks

Enno

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Enno Rey

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On Sun, Oct 16, 2011 at 04:02:38PM +0800, ar wrote:
> ??? 
> 
> Can somebody tell me why this route is being prefered?
> 
> I have 2 customer edge router. one on each site. The are linked together running ospf for intra-area routes. Multihomed to the MPLS VPN service provider using OSPF also as PE-to-CE? routing protocol. Routes are redistributed so they are both E2 routes.
> 
> Here's the outpu from one of my CE. I am trying to check show ip route the loopback address of CE2 from CE1.
> 
> 
> Here's the route of CE-2's loopback via the MPLS/VPN
> 
> 
> CE1#sho ip route 10.30.30.30
> Routing entry for 10.30.30.30/32
> ? Known via "ospf 10", distance 110, metric 1
> ? Tag Complete, Path Length == 1, AS 10, , type extern 2, forward metric 1
> ? Last update from 172.16.2.1 on FastEthernet0/0, 00:01:47 ago
> ? Routing Descriptor Blocks:
> ? * 172.16.2.1, from 10.2.2.2, 00:01:47 ago, via FastEthernet0/0
> ????? Route metric is 1, traffic share count is 1
> ????? Route tag 3489660938
> 
> 
> Here's the CE-2's loopback via the Intra-area link. (elected as best path always)
> 
> CE1#sho ip route 10.30.30.30
> Routing entry for 10.30.30.30/32
> ? Known via "ospf 10", distance 110, metric 20, type extern 2, forward metric 1000
> ? Last update from 172.16.3.1 on FastEthernet1/0, 00:00:08 ago
> ? Routing Descriptor Blocks:
> ? * 172.16.3.1, from 10.30.30.30, 00:00:08 ago, via FastEthernet1/0
> ????? Route metric is 20, traffic share count is 1
> 
> 
> Loopback IP is just redistributed to OSPF so it should be an E2 route.
> 
> However based on the two routes above, the one via the intra-area link is always being prefered over the one via the MPLS network even if I adjust the redistribution metric. Both are E2 routes already. What's the difference between the two routes and why the other is being prefered always regardless of metric set?
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-- 
Enno Rey

ERNW GmbH - Breslauer Str. 28 - 69124 Heidelberg - www.ernw.de
Tel. +49 6221 480390 - Fax 6221 419008 - Cell +49 174 3082474
PGP FP 055F B3F3 FE9D 71DD C0D5  444E C611 033E 3296 1CC1

Handelsregister Mannheim: HRB 337135
Geschaeftsfuehrer: Enno Rey

=======================================================
Blog: www.insinuator.net || Conference: www.troopers.de
=======================================================