[c-nsp] Outbound Load balancing using eBGP

[RAZ MUHAMMAD]

Hi Roger,

Thanks for your response.
Unfortunately the vendor does not support multipath or anything similar on
their platform. I am left with usual BGP attribute manipulation tricks, such
as weight or local AS preference. Our eBGP router is multi-homed and is
getting full Internet routing table from both ISPs.
Its difficult to devise a deterministic outbound load sharing policy with
full routing tables. I am not sure how would I slice the full table and
define a policy to share the outbound traffic across 2 transit providers. If
it was a default route only option from both transit providers, then
outbound load sharing would have been a lot easier to some extent.
I am also considering the default route only option from both providers, or
have the default route and some partial routes from the transit providers.
But I am trying to evaluate the pros and cons of either having the full
internet routing table or just a default route from the upstream provider.
The obvious advantage would be easier outbound load sharing across both
providers, less resource utilisation on the router (though our BGP router is
fully capable of handling full routing table). The disadvantage that comes
to my mind would be having less control over traffic, and more dependence on
transit provider's BGP policy.

I would appreciate if someone can shed some further light on using the
default route or full routing table scenario while multi homed. In this case
hardware is not an issue, I am trying to assess the operational,
differences, or the outcome in terms of traffic patterns.

Regards


On 21 December 2010 11:16, Roger Wiklund <copse at xy.org> wrote:

> On Mon, Dec 20, 2010 at 10:30 PM, RAZ MUHAMMAD <raz.muhammad at gmail.com>
> wrote:
> > Hi all,
> >
> > I would like to find out how one can use BGP to load balance outbound
> > traffic, while multi homed to 2 transit providers or ISPs and getting
> full
> > routing tables, no default routes? The BGP peer at the client end is a
> non
> > Cisco router, so would not be able to use the multipath feature. The load
> > balancing is intended for all routes in the routing table, or at least to
> > achieve some kind of load distribution.
> >
> > Is there any other way to achieve an optimal outbound load balancing
> method
> > using eBGP?
> >
>
> Just do "maximum path 2" to loadbalance on equal paths. Per session is
> default.
> Also if you want to ignore as path use "bgp bestpath as-path
> multipath-relax"
>
> If your non Cisco router is capable of handling full routing table,
> surley it must support at least multipath. Check with the vendor.
>