BGP 2 paths to same router

[carl_townshend]

Hi all

If I had 2 iBGP routers connected to each other via 2 links, a 2 meg link and a 10 meg link, what does BGP do and use to decide which link to use?

cheers

Carl

[Stephane Bonnet]

Hi,

The best way to understand BGP and its process decision, throw an eye on this article:

BGP Best Path Selection Process

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml

You can use your 2 links but with a 1:1 ratio, aka equal cost multipath. Because the two BGP neighbors are iBGP (same AS), you cannot use bgp unequal cost multipath, it's only between eBGP neighbor (AS different).

The best way to achieve your unequal path loadbalacing between your two routers perhaps using an IGP which can do that like EIGRP and rely on it.

All is detailed on this link for BGP best path selection algo.

HTH

Stephane