Transit Analysis

Fri Feb 15 17:51:37 UTC 2002

      Guy.Ram at usa.telekom.de wrote:
    > When trying to identify good AS candidates for peering from your transit
    > traffic stream. It would seem that distinguishing the ingress traffic by
    > not only the next-hop AS but also by the next-next-hop AS (or by the
    > complete AS path) so that you can identify which customer or peer of your
    > transit provider might be a likely interesting new peer for you. However,
    > due to the concept of BGP traffic in the internet being asymmetrically
    > distributed. It is not possible to exactly determine the real AS path of
    > incoming traffic. The only reliable information is about the next-hop and
    > the origin AS.

Correct, and you can't generalize by assuming the traffic to by
symmetrical, as it isn't far more of the time than it is.

In my work, I've always looked at the entire AS-path on outbound traffic,
and done a weighted assignment of bytes-through to each AS in the path.
For inbound traffic, basically all you can do is look at the origin AS by
itself.  The neighbor you receive it from isn't interesting, because
that's who you _currently_ receive it from, and the whole point of this
exercise is to determine who _else_ you could receive it from if you added
peers.

                                -Bill