Revealed: The Internet's well known BGP behavior

Florian Weimer fw at
Sat Aug 30 00:55:40 CDT 2008

* jim deleskie:

> Announcing a smaller bit of one of you block is fine, more then that
> most everyone I know does it or has done and is commonly accepted.
> Breaking up someone else' s block and making that announcement even if
> its to modify traffic between 2 peered networks is typically not
> looked as proper.  Modify your taffic good. Do it to anyone other
> traffic = bad.

No, the idea would be to do this to your own prefixes/traffic.

           +------/AS 2/-----/AS 3/--------+
           |                               |
        /AS 1/                          /AS 4/
           |                               |
           +----------/AS 5/---------------+

I'm AS 1, and the link to AS 2 has a bad metric from my POV.  AS 4 uses
local preference (or something else I can't override by prepending my
own AS) to route traffic to me through AS 3 and AS 2.  Now I prepend
AS 4 to my announcement to AS 2, and voilà, the traffic flows through
AS 5, as desired.

No prefix hijacking has occurred (I would have received the traffic
anyway, just over a different path), it's just traffic engineering.
(But probably a variant that is generally frowned upon.)

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