Tulip Rasputin wrote: That's why i explicitly asked for some "social/political/etc." reasons where an ISP may not want his traffic to traverse some particular AS number(s). Something which is beyond BGP to determine as of now ! :-)

FWIW, this is exactly how I understood the question. It's all about "non-BGP" issues.

I believe with the responses that i received both on the list and offline, that it is indeed quite normal for ISPs to filter routes based on the AS Paths for 'other' reasons. Reasons, quite beyond BGP as a protocol to handle! And this can happen, when an ISP doesnt want its traffic to traverse some AS(es).

I'm not sure I agree with "normal", but it is common practice indeed, a significant part being in a <cough> grey <cough> area, and notice that nobody dared to post the reasons on the ML. Trying to stay intellectually honest, there are "good" and "bad" reasons for it. Using my well-known politically incorrect bluntness, I would say this (words borrowed from several people) (disclaimer #2: this is somehow exaggerated, but here it is anyway): God has given men a brain and a penis, but not enough blood to operate both of them at the same time. Although there are exceptions, when the blood flows to the brain, men use BGP; when the blood flows to the penis, men manipulate the AS_PATH and/or create route-maps :-D Michel.