[c-nsp] load share eBGP and iBGP

[Oliver Boehmer (oboehmer)]

> 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.

So you are aware that whenever R1 load-shares traffic to R2, you need to
be very sure that R2 fwds the traffic towards the PE, as you would run
into a loop? 
If you do accept this, you could move your traffic into a VRF on R1 and
R2, and make use of "maximum-paths eibgp" feature to load-share traffic
across ebgp and ibgp peers. This feature is intended to be used on PEs
(hence only suppt in VRFs) along with label swichting to avoid the
potential for loops, but it could also "work" in your environment, with
the above caveat.

If you go down the "turn ibgp to ebgp using local-as" route and use ebgp
multipath, I guess you also need "bgp bestpath as-path multipath-relax"
to compare ebgp paths with different as-path

A "proper" way would be some form of a tunnel (GRE?) between PE and R1
via R2 with an eBGP session across it, and you can do normal ebgp
load-sharing on R1, and the tunnel would address the potential for
loops.

Alternatively (but again with possible loops) you can build an eBGP
multihop session between PE and R1 via R2, and also do regular ebgp
load-sharing.. I've seen customers do this, but it requires the
PE/provider to cooperate.

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