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Webcast-Catalyst9k
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Using BGP4 TO PROVIDE RESILIENCE AND LOADBALANCING

I am involved in a project which requires the redesign of a private network to one using a service providers MPLS platform. The design needs to provide for routing during migration and ISDN backup.

The client is runnig EIGRP and I am intending to run BGP4 on two links into the service providers autonomous system from two geographically dispersed sites but connected with 10M LAN extension service.

I want to provide router & circuit resiliency between the sites and provide load balancing on the links using LOCAL_Pref and MED attributes.

I am having difficulty understanding which of 4 routers I should run iBGP4 only and which should run both EIGRP and BGP4 to provide a resilient and load balancing solution.

I have a diagram that I can share showing the senario and my thoughts on the subject.

2 REPLIES
Gold

Re: Using BGP4 TO PROVIDE RESILIENCE AND LOADBALANCING

As long as you're not transiting traffic, just run it on the two routers directly peered to the service providers. From there, adjust the local pref (med won't do you much good, most likely) to adjust your outbound load. To adjust your inbound load, use as path prepend. Make certain both routers can handle at least two views of the entire internet routing table.

Another option is to accept partials only from each provider, and shoot for optimal routing, rather than load sharing.

Russ

New Member

Re: Using BGP4 TO PROVIDE RESILIENCE AND LOADBALANCING

I would run IBGP between the two AS boundary routers, over the 10 Mbps link. EBGP will be used over the 2 links to the ISP AS.

It's not easy to achieve load balancing with EBGP in your scenario. However you can apply AS prepend or MED to some of your routes using an outbound route-map towards the ISP. The route-map will be applied on the EBGP neighbor statement on both of your peering routers A and B.

Router A will advertise a particular set of internal networks with a lower MED (or shorter AS path) to your ISP than router B.

Conversely, Router B will advertise the remaining set of routes with lower MED (or shorter AS path) than router A.

This way each router will advertise all your internal routes to your ISP but some are preferred through router a and other through router B. Therefore the inbound traffic (from ISP to your EBGP routers A and B) will be deterministically load balanced per destination subnets.

If router A connection to your ISP fails, router B can take over. It is still advertising all your internal networks to your ISP. The IBGP session between routers A and B will be used as backup. Router A can redirect the internal traffic to the ISP through the 10 Mbps link to router B.

The outbound traffic load balancing is more difficult to control. The way I would do it is to redistribute EBGP into EIGRP with exactly the same metric value on both routers A and B. The EIGRP routers 'closest' to router A will then hopefully send Internet outbound traffic to A (lower cost than B) and routers 'closest' to B will send outbound Internet traffic to router B.

I hope this helps.

Thanks

Karim

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