Dual Site BGP Failover

Unanswered Question
Feb 19th, 2010

Working on a designfor Interconnecting two sites and providing a DR solution at the same time. What I propose to do is basically announce two /24 blocks of IP space from each site using BGP to two separate providers. The two sites will have an iBGP link between them and will trade routes with each other. The idea would be that if a connection or router goes down at site A for example, inbound traffic destined for site A;s networks will start to reroute over through site B and vice versa. I have included a diagram that should illustrate what I am trying to do. Would like to see if anyone could comment and point out any glaring deficiencies inherent in this design. The diagram shows a single DS3 between the two sites but there will be two for redundancy. Another idea was to have an MPLS connecting the two sites and running iBGP over that. I am not totally sure that can be done or if it can how. Also would like to see if anyone could maybe propose a better idea for how to achieve this. As always thanks for your time netpros.

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Giuseppe Larosa Mon, 02/22/2010 - 00:41

Hello Rfranzke,

you should use BGP conditional advertisement in order to be able to have the still alive site to start to advertise the /24 of the other site:

see

http://www.cisco.com/en/US/docs/ios/12_4t/ip_route/configuration/guide/t_brbbas.html#wp1111262

http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cbgp.html#wp9085

This may be the right tool for this job.

Hope to help

Giuseppe

rfranzke Mon, 02/22/2010 - 07:23

Thanks for the reply. I had considered using this but if I am not mistaken this will

have one site not announce the routes until such time as some kind of event happens

which then triggers the site to start announcing the routes. Looking at the diagram I have attached, Site one announces one network and is configured to conditionally announce the other network site two and site two announces one network and is set to conditionally announce the network from site one. Am I correct with this here? I was trying to actually have both networks come in over both links to maximize usage of the links all the time. Then if there was a failure of one link at say site one all traffic would reroute through site 2. Using the conditional advertisement would help me keep traffic off the link between the sites I suppose which would be good. Also I assume with the conditional advertisement both providers would still need to be willing to announce the other providers netblocks just as with any multi-homed setup. Also with the conditional advertisement, for this to work will I need to accept full tables from both providers in order to get the other sites prefixes in the BGP table? Many thanks for the help here. As always you guys really are a great resource.

rfranzke Mon, 02/22/2010 - 07:40

OK nevermind about the full tables question. After additional reading I see how this works now. Was a little confused for a second. Thanks again.

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