ISP Policies

["Tulip Rasputin" <tulip_rasputin () yahoo ca>]

Hi,

I have a general policy question.

Do the ISPs ever look for some particular AS number in the BGP AS_PATH and 
then decide what action/preference/priority they need to take/give based on 
the AS number(s) present in the BGP AS_PATH_SEQ/SET? For instance, does it 
happen that an ISP receives some BGP paths, but because of some political, 
social, economical, DOS attack, etc. reasons decides that it doesn't want to 
accept this path because some particular AS number is present in the BGP 
UPDATE.

Basically, it doesn't want *its* traffic to flow via that particular AS 
number(s).

Or, if there is a mutual disagreement between two ISPs, and one doesn't want 
his traffic to traverse the other's AS number.

Does this sort of thing ever happen? Are such restrictive policies normal in 
the ISP/IX scenarios?

Thanks,
Tulip