Load balancing default route from two ISP on one BGP router.

[Stephan Nandelstadt]

Hi all,

I have two uplinks to ISPs on one router in which they give me only default routes via BGP. I'm looking for the best way to load balance acrross both circuits with minimal config.

[trung.nguyenxuan]

Hi Stephan,

Let us know in more detail. Do you have 2 ISPs or only one? Bandwidth of both uplinks are the same? And what is the prefix length of your subnet?

[Jose Jara]

Hi,

if you have two links to different ISPs on one router and you are receiving the default route and all attributes are the same: weight, local preference, origin, as-path length and MED , you can use the command bgp bestpath as-path multipath-relax in order to achieve multipath load sharing. Be aware that the AS-PATH length must be the same, even though the AS of the two ISPs will be different. Otherwise, different lengths, it will not work.

Hope this helps,

Jose.

[Joseph W. Doherty]

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Posting

In addition to what Jose describes, you may need to set maximum-paths 2 for BGP (I believe the default only allows 1 route).

[Jose Jara]

Joseph,

good point. Yes, it is needed the maximum paths 2.

Thanks,

Jose.

[Stephan Nandelstadt]

I have uplinks to two seperate ISPs and receive a only receive a default route from each via BGP. Both links are the same speed and BGP is used only to advertise our prefixes out - nothing hectic. I was thinking the easiest solution would be to add two static routes on the router and balance across. I had read about applying the command "

bgp bestpath as-path multipath-relax", but wasn't sure since from my understanding it's not a fully supported command with Cisco. We'll see.