Revealed: The Internet's well known BGP behavior

jim deleskie deleskie at
Sat Aug 30 09:35:16 CDT 2008

The biggest issue with using a heavy hammer to effect traffic is that
you don't always know why the other side is routing the way they are.
Could be simple cost (peer vs transit) or a larger issue like
congestion.  Either way think before you route.

I'm thinking Pandora's box hasn't just been opened but blown apart.....


On Sat, Aug 30, 2008 at 2:55 AM, Florian Weimer <fw at> wrote:
> * 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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