BGP Load Balancing

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Mar 4th, 2009
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Hi, can anyone tell me if I have two protocols running in network one is eigrp & another is bgp. I am having same routers for destinations learning from BGP & eigrp ..can I do load balancing between BGP & eigrp or if is there any other possiblity to achieve load balaning in this case..

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Giuseppe Larosa Thu, 03/05/2009 - 00:09
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Hello Jain,

if routes are from two different routing protocols is difficult to achieve load balancing.


with default settings:

most specific route is installed and used

the better (lower) AD is preferred

if AD is the same the lowest metric is preferred


so to achieve load balancing you should:

have the same set of routes learned on both protocols with the same prefix lenghts.

you should make the AD equal (this can be done)

you should make the metric equal:

EIGRP metric is dynamic any change in the topology could cause a change in metric.

BGP can carry a metric (MED attribute) or not)

you can set the metric on receiving routes with a route-map applied to the neighbor.

But this metric is static : it cannot change over time.


If you can control one of the two paths the suggestion is to change so that you use the same protocol on both paths.


for example: if you can control the EIGRP path and you cannot use it on the other path you can change to use BGP also on the first path


you then need


router bgp xx

maximum-paths 2


notice that if the current BGP neighbors are eBGP you need to build an eBGP session on first path


Hope to help

Giuseppe



royalblues Thu, 03/05/2009 - 00:14
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I am afraid this wont be possible with BGP.

BGP path selection does not take into account the administrative distance so even if you try to make the AD of the routing protocols same, it wont work.


Narayan

Joseph W. Doherty Thu, 03/05/2009 - 04:58
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". . . is there any other possiblity to achieve load balaning in this case.."


Well, depending on the environment, you might configure tunnels across both paths and run the same routing protocol treating the tunnels as the primary paths.


You might also be able to tunnel across one path and match the routing protocol on the other.


You might be able to iBGP or multi-hop eBGP across the EIGRP path.


You might be able to use OER/PfR to override both routing protocols and dynamically load balance.

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