config For backup link

Unanswered Question
Jan 23rd, 2009


DR user accessing branch via 45 MB link DC Router.We configured EIGRP between DR and DC.Also configure a BGP between DR and ISP.Branch router having static route.

ip route

ip route

ip route

We proposed a backup link 5 MB for branch in case of DR Router Failure.

can any one tell me how it will be possible?

What config is required on DR, DC and branch router.

Thanx in Advance...

I have this problem too.
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kwillacey Fri, 01/23/2009 - 06:40

I think you would need to turn on dynamic routing on the back up link interface on the DR router in that case it looks like it would be BGP. Assuming of course that the MPLS cloud has static routes to the branch and redistributes them into BGP that is.

It seems your EIGRP routes on DR would be external with an AD of 170 so when you learn those same branch routes via eBGP it will have an AD of 20 and use the backup as the primary path. The easiest thing to do to fix that would be to change the eBGP routes AD to something greater than 170. I'm sure there must be a better way to do it but I just can't think of it right now..... I'm sure a real expert could tell you.

arjunsawant Tue, 01/27/2009 - 19:56

Thanx...for reply.

I appreciate with u.

can u pls brief config.

Is there any another soln?

kwillacey Wed, 01/28/2009 - 05:59

I don't know what your AS number would be but your BGP config would look similar to what you currently have on the DC router, with the following command added 'distance bgp 200 200 20'.

I suppose depending on how the MPLS cloud is setup that you could use poisoned static routes on the DR router, which could work based on how your branch is setup.

ip route x.x.x.x y.y.y.y 200

where x.x.x.x and y.y.y.y is the subnet and mask of the branch office.

hope this helps

arjunsawant Thu, 01/29/2009 - 06:33


I am going to configure BGP for my backup link.

On which router i have to put static route as u mentioned.

ip route x.x.x.x y.y.y.y 200

Is it on DR router?

If yes, my branch network is learn via BGP.

can u pls explaine the command "distance bgp 200 200 20".

Thanx for ur reply.....pls be in touch.

kwillacey Thu, 01/29/2009 - 06:46

If you are going to run BGP on the DR router then you would not need the static route/s.

However the BGP routes would be used as primary because they would have a better administrative distance than the EIGRP routes that point to the branch, the lower the AD the better. So to ensure that the BGP routes are only used when the DR router loses the EIGRP routes you would need to change the AD of BGP.

router BGP XXX

neighbor remote-as xxx

distance bgp 200 200 20

That command modifies the AD of BGP which works as follows.

bgp (external) (internal) (local route)

So now that the external BGP AD has been changed to 200 the EIGRP routes with an AD of 170 will be in the routing table.

Hope this helps.

arjunsawant Fri, 01/30/2009 - 06:43

Hi...have a good Day.

I have some doubt.

1.If i access any branch pc from DR,it takes path through DC(EIGRP), how it will take return path.(Via DC or via backup link)?

2.If i access any server in DR from Branch,how it will take path(via DC or via Backup link).Is there required any floating static route on branch router?

I m very thankful to U......

cisco.com123 Thu, 02/05/2009 - 22:00

Hi Arjunsawant,

i have one doubt that you are saying and as per your diagram, you have puchased 5mb backup link but i am not understanding your sentense as below

"We proposed a backup link 5 MB for branch in case of DR Router Failure"

arjunsawant Fri, 02/06/2009 - 03:02


Just go thr my net Diag which i attached.

My backup 5 MB Link is at DR which is used when my DC router fail (Router redundancy).


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