about interdomain multipath routing.

Matthew Petach mpetach at netflight.com
Tue Nov 10 09:23:13 UTC 2009

On Tue, Nov 10, 2009 at 1:10 AM, Doug Lane <laned1 at gmail.com> wrote:
> On Tue, Nov 10, 2009 at 3:50 AM, Matthew Petach <mpetach at netflight.com> wrote:
>> I've outlawed the use of multihop eBGP for load-sharing here; when we get
>> multiple links off the same router to a peer or upstream, they are configured
>> with multipath.  We've got hundreds of BGP sessions across the network
>> configured with multipath on them.
> Do you use iBGP multipath as well to load-balance between links on
> different routers?


> I know eBGP multipath is fairly common, but I wonder how many are
> using iBGP multipath as well. I doubt any carriers would support it,
> so it's probably only useful for load-balancing outbound traffic. The
> problem with eBGP multipath alone is that you might want to terminate
> circuits from a given carrier on two different routers for redundancy
> reasons, but that precludes any load-balancing with eBGP multipath.
> Obviously your network has to be designed with equal-cost paths for
> iBGP multipath to be of any value.
> -Doug

iBGP with multipath, multiple LSPs to each BGP next-hop...much load
balancing across all same-cost internal links to each of the eBGP
multihop next-hops.

inet.0: 300787 destinations, 2675963 routes (300092 active, 2
holddown, 2086 hidden)

Yes...takes up a chunk more memory keeping track of all the
different paths, but it does provide more end-to-end load balancing
of traffic even on different routers.


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