[c-nsp] load share eBGP and iBGP

[Tony]

Hi Oli,

Thanks for your comments & suggestions.

--- On Mon, 14/2/11, Oliver Boehmer (oboehmer) <oboehmer at cisco.com> wrote:

> From: Oliver Boehmer (oboehmer) <oboehmer at cisco.com>
> Subject: RE: [c-nsp] load share eBGP and iBGP
> To: "Tony" <td_miles at yahoo.com>, cisco-nsp at puck.nether.net
> Received: Monday, 14 February, 2011, 6:35 PM
>  
> > 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? 

Yes, I am aware of this issue and the potential for problems here.

> 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.
> 

I did find this command in my searches to find a solution that would work, but was disheartened when I found that it only worked in VRFs. R1 & R2 are 877 on the end of DSL services, so I don't really want to run VRFs on them (as well as they only support VRF-lite).

> 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

This might be the command that I am missing to make this work, I'll have to test tomorrow.

> 
> 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.

Problem with that approach would be MTU issues as we cannot increase the MTU on DSL session.

> 
> 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.
> 

We control all routers in this scenario (PE, R1 & R2) so that could work. So would doing this give us TWO BGP sessions bewteen R1 & PE, one over direct connection and the other via R2 ?

Even though we control/maintain R1 & R2 we don't "own" them, so they need to stay as two separate 877 devices. The PE is our 7204.

I'll have to give some thought to the various options and test which ones will work in our setup and then decide on the best one.

Thanks,
Tony Miles.