backup link problem, please help.

Unanswered Question
Jun 10th, 2009

Company C has servers on my network(company B). Users on company A network access these servers via company C the red link.

B has a link to A as I need to access servers on A's I redistribute network in to our EIGRP.

Company C uses my link from B to A (blue) as a backup to reach network I have created static routes with an AD of 200 to network pointing to A. As these have a higher AD than the other static route which point to C these are not entered in to the routing table. The problem I have is I have no idea if the etherflow link from C to A fails so there is no automatic failover for C to use my link to A.I have to use a manual process and remove the routes for network which point to C.

Myself (B) and C use EIGRP AS 100. our networks don't share routing information due to the passive-interface command.

My question is what would be the best way to achieve autmamtic failover should C's link to A fails. I know we could share complete EIGRP information but I don't want to know all of their routes. Someone has suggested using a new EIGRP AS (110) which will work around the existing AS (100) but I'm not sure this will work.

Please could someone advise on a prefered method.

Many Thanks

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Dennis Mink Wed, 06/10/2009 - 05:19

Darren, I might be missing the complexity of this set up, but what if you add a static route on

ip route and redistribute this into eigrp 100

also add a to and redistribute into eigrp.

then make tweak the metrics for that last static route so it becomes less preferred and only active when the primary link fails.

darrenriley5 Wed, 06/10/2009 - 06:37

Sorry my diagram wasn't correct I've updated it. The basic problem I have is the three companies are not sharing routing information so how would I know if company C's etherflow connection to A failed. My router would continue forwarding traffic for network via C ( C then wouldn't have anywhere to send the traffic. Currently I have to remove my static routes on company B switch so the backup route kicks in on the router. I need to find a solution so this will happpen automatically. The easy solution would be to use EIGRP AS 100 across all 3 companies and share all of each others routes. This isn't something I would like to do as I don't want A & C having routes to all my subnets. Someone sugggested setting up another EIGRP AS just for this purpose but I'm not sure how this would work.

Dennis Mink Wed, 06/10/2009 - 17:04


I understand you don't want full routing distribution between customers. The thing is that is you want automatic fail over when the - link fails to go via the link between &, you will need dynamic routing and updates between companies, no way around that; this will propagated an alternative route into company C in case the primary link fails.

By sticking company C in its own EIGRP AS, you have the opportunity of filtering out what updates you want between the companies/AS's (use route maps to do this for instance)


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