[c-nsp] BGP Multipath load balancing

[gscisco@xs4all.nl Cisco]

On 5/23/06, David Coulson <david at davidcoulson.net> wrote:
>
> gscisco at xs4all.nl Cisco wrote:
> > -Then again you might want multiple (physical) routers to connect to
> your
> > upstream in different pop's for resilliency. That way you can do a
> traffic
> > analysis and try to find a split even point (you will of course need to
> > review that to make sure it will continue to work) and then prefer
> certain
> > routes from others in BGP (local pref and such). And specify MED's/AS
> > prepends for incoming traffic.
>
> I don't have multiple paths into the same exterior AS, so MED isn't
> going to help. Network looks like this (from a BGP perspective)
>
>
> ISP A    ISP B
> |        |
> |        |
> R1-------R2
> \        /
>   \      /
>    \    /
>     \  /
>      R3
>
> There are multiple R3 routers all meshed with R1, R2 and each other.
>
> > - a nicer solution keeping you equipped with multiple physical routers
> for
> > redundancy would be to run GLBP between the routers. That would load
> balance
> > your egress traffic automatically.
>
> Yeah, GLBP seems like a good solution, although since most of my
> customers are on /29s with a single IP sending traffic on their end,
> GLBP is probably not going to do much (unless they have a per-flow or
> per-packet load-balancing technique that I missed).


I think you can configure GLBP on a load basis but this might not work for
you if you have very few hosts actually sending data, though it might be
possible it will not utilize properly your connections.

>From what I find at cisco it is not doable to load balance between 2
different ISP's
See their website at:
http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf5

Of course, I'm also trying to figure out why downstream routers (e.g.
> R3) with BGP into both of my edge routers won't do multipath route
> loading into the RIB even though iBGP multipath is enabled and I'm
> allowing up to six paths within my BGP config. Does it not multipath
> them if they originated from two different ASes? before being
> redistributed via iBGP?


David
>
>
I think it should work but have never seen it; only eBGP multipath. Maybe
you can put your R1 and R2 in a different AS as R3 then it will become eBGP
multipath. Of course you can also redistribute it in for example OSPF and
EIGRP as then the AS path is gone and it definitly load balance between
them.