Prepending with another ASN you don't own

Randy Bush randy at
Fri Dec 16 23:22:42 UTC 2016

>> this is called path poisoning.  an italian friend used it in his phd
>> thesis.  a few friends and i used it to detect use of default across
>> the internet.
> I've done this in the past as a work-around for insufficient BGP
> community support.  Just prepending the AS I wanted to ignore the
> paths.
> But, if the problem is an anycast CDN choosing a sub-optimal path to
> reach you, you might try reaching out to them.  They're probably just
> as, if not more interested, in getting their traffic to you as
> efficiently as possible.

apologies.  i should have been more explicit.  both of the examples
were using path poisoning for routing research.  it is not a technique
i would reccommend in normal operations.


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