[c-nsp] Load balancing outbound traffic with BGP

[Matyas Koszik]

You may want to try

bgp bestpath as-path multipath-relax

to achieve load-sharing accross the providers, with different (but equal
length) as-paths. (Works for me like a charm in a situation similar to
yours.)




On Tue, 26 Feb 2008, Jeff Chan wrote:

> Hi All,
> Given multiple, roughly equal upstreams (Sprint, ATT, Level3)
> providing full BGP tables to a small ISP, what's the best way to
> balance the outbound traffic?  The problem is that all else being
> equal (path length, local pref, etc.) BGP decides to take the one with
> the lowest peering IP address.  Given that the upstreams have
> many/most of the same customers and peers, the peer with the lowest IP
> address seems to win too often, meaning it does too much outbound
> compared to the others.
>
> I asked the same question some time ago and the common practice answer
> seemed to be prefer traffic for some other large networks (UUNet,
> Qwest, AOL, etc.) over the peers with higher IP address.  Is this
> still the case?  Seems kind of an ugly hack, but it works.
>
> Are there any other approaches?  How about jumbling up or staggering
> the local preferences:
>
> ISP S:
>
> customers: localpref 120
> peers:     localpref 110
> others:    localpref 100
>
> ISP A:
>
> customers: localpref 110
> peers:     localpref 100
> others:    localpref  90
>
> ISP L:
>
> customers: localpref 100
> peers:     localpref  90
> others:    localpref  80
>
> Where S has the highest IP address, A next highest, L lowest.  Haven't
> tried this; just a thought to try to compensate for the IP address
> decision.
>
> Cheers,
>
> Jeff C.
>
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