Routing Problem

Unanswered Question
Feb 28th, 2010

Hi, I need help on routing issue

HQ connects to DR site via 10mb fiber link
Branch office connects to HQ via service provider MPLS cloud
To overcome single point of failure for branch offices we got MPLS at DR site.

When HQ MPLS link goes down ; all branches cannot access HQ

Branch_router=====Service-Provider_router=====HQ_MPLS_RTR--------BackBone_RTR

Branch_router=====Service-Provider_router=====DR_MPLS_RTR--------BackBone_RTR

HQ_BackBone_RTR---------------------------DR_BackBone_RTR

Routing protocol on LAN : OSPF
Routing protocol for MPLS : BGP


On DR MPLS_RTR I get all routes for branches but these routes are not forwarded to DR Backbone_RTR,
there is already mutual redistribution, can you experts help on this.

How to manage getting updates from two different source to same destination on Backbone_RTRs

configuration attached

thanks to all

I have this problem too.
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Lei Tian Sun, 02/28/2010 - 12:49

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Hi,

A quick look of your configuration, you are missing

1, keyword "subnets" when redistributing bgp into ospf.

2, keyword " match external" when redistributing ospf into bgp. By default only ospf internal route will be redistributed into BGP, if you want the ospf external routes get redistributed into BGP, you need to use match keyword.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800943c5.shtml

Also be aware when doing mutual redistribution, loop might occur.

HTH,

Lei TIan

saquib.tandel Sun, 02/28/2010 - 13:01

thanks for replying

mutual redistribution is needed, how to overcome the loop concern.

Lei Tian Sun, 02/28/2010 - 13:13

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Hi,

There are multiple ways to prevent loop when mutual redistribution is required; it might vary on each network. You need to look closely on the network and how the route flows.

In general, you can tag the routes when it redistribute from protocol 1 into protocol 2, and block those routes when redistribute from protocol 2 back to protocol 1.  Same rule for redistributing protocol 2 into protocol 1.

You can find a good reference for redistribution

http://blog.internetworkexpert.com/2008/02/09/understanding-redistribution-part-i/

HTH,

Lei Tian

saquib.tandel Sun, 02/28/2010 - 21:47

Thanks link is very useful

Can you help with cisco link with config examples and more complex scenarios.

IE (part II ) on redistribution is kool as well

thanks again

Lei Tian Mon, 03/01/2010 - 05:50

Hi,

I couldn't find a good reference on cisco.com, but you can consider a cisco press book "Optimal Routing Design" by Russ White.

HTH,

Lei Tian

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