[c-nsp] load share eBGP and iBGP

[Tony]

Hi all,

I have a situation where I wish to load share traffic between two services.

We have a PE router that terminates a DSL session from two CE routers, R1 & R2. R1 & R2 are at the same location and share the same LAN network.

R1 is the default gateway for the network at this location and I want it to do load sharing on both of the links (ie. the one from R1 and also R2). I'm aware of the problems/issues that can/may arise, but this is what would like to be done.

R1 & R2 talk eBGP to PE. R1 & R2 also talk iBGP between themselves (as they in the same AS on the LAN).

With the setup this way R1 only adds a single route (via its DSL link) to the route table as it is an eBGP route and they are preferred over iBGP routes. I know that I can never make an eBGP & iBGP route look the same to R1 (by changing metrics, or other) so this will never work how it is.

I was doing some research into ways of making it work and I came across the option of replacing the AS on each end of the iBGP session (using "local-as xxxxx no-prepend replace-as") to turn the iBGP into eBGP. This works fine (in that it's now an eBGP session), but the routes are still not equal cost as the one from R2 has a longer AS-PATH now.

I'm after any suggestion on how to make R1 get both BGP routes (one directly from PE and one via R2) and make them equal cost so that it will load share across the two links. One option that I can think of is to use a route-map on the BGP session between PE & R1 to prepend to the AS-PATH so that they are the same length. Are there any other options or is this the only/best way to achieve this ?


Thanks,
Tony Miles.