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Re: Split flows across Domains
From: Robert E.Seastrom <rs () seastrom com>
Date: Tue, 24 Jan 2006 12:07:34 -0500



"Christopher L. Morrow" <christopher.morrow () verizonbusiness com> writes:

On Tue, 24 Jan 2006, Robert E.Seastrom wrote:



Glen Kent <glen.kent () gmail com> writes:

For example, an ISP can learn two different equal cost routes to a
foo.com server via two different autonomous domains. It can thus split
different flows (based on src-dest IP, src-dest Port, TOS, etc) across
these two paths.

Do operators currently do this?

Folks can send me replies offline in case this constitues a "trade secret"!

Works great with a flow-based router (or layer-three-switch-pronounced-
'crippled-router').  The downside, of course, is that you now have a
flow-based router in your network, which has been shown to Not Work
Well under other specified conditions (worm outbreaks come immediately
to mind).

I could be mistaken, but this is also a feature in mbgp, effectively
loadsharing across two external paths. I presume the paths would have to
be completely equal all the way down to the router-id and (probably)
age-of-route ...

He said "via two different autonomous domains", which I took to mean
two upstreams... and my understanding is that (on ciscos anyway)
you're talking per-packet, not per-flow load balancing.

What happens when you intentionally bugger stuff up so that you are
per-packet load balancing your outbound traffic between two diverse
(ie, non-congruent-to-the-same-upstream-and-pop) paths is left as an
exercise to the reader...  but I don't think TCP is gonna like it. :)

                                        ---rob



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