BGP failover issue

Unanswered Question
Jun 29th, 2009

Hello all,

We are having multiple links to our core site using bgp .

one is shdsl and other is fiber.

We have bgp and As no. provided by ISP .BGP is taken care by isp.

on our remote site we have 2 interfaces configured with wan ips and as no.

Both wan ips have same AS no. and both are displayed in IP BGP summary .

In sh ip BGP route, both wan links ips are visible.

But if one wan link goes down other is not coming up automatically.

what configuration required to make failover automatically.



I have this problem too.
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cisco_lad2004 Mon, 06/29/2009 - 03:25


If you are multihomed as you explained and both BGP sessions are established then you have redundancy.

In you set up, you see that there 2 entries for a given prefix one from each peer but only one as best.

When you test failover, best entry will move on to the only available peering session. It might take some time (max 180s) but it would failover.

If you have more troubles, let us see the sh ip bgp summary, and show IP BGP for a given prefix.



mkareemashraf Mon, 06/29/2009 - 04:17

Thanks for your quick respose.

we cannot wait till hold down time expires. we have one fiber connectivity which will not go down frequently .so i want to make this link primary.

Please can u help for me the configuration to make one bgp link primary.

your help is highly appreciated.

cisco_lad2004 Mon, 06/29/2009 - 04:37

to make a link primary, I usuallt rely on AS prepend.

Using a route map towards the BACKUP neigbour:

Prepend ur AS twice outbound.

Prepend ur provider's AS twice inboud.

The above will ensure that BACKUP session has a longer AS path and therefore less preffered.




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