On Fri, Jan 27, 2006 at 11:39:27AM -0500, Joe Abley wrote:
On 27-Jan-2006, at 11:12, bmanning@vacation.karoshi.com wrote:
but by definition, the right-most entry is the prefix origin...
Suppose AS 9327 decides to originate 198.32.6.0/24, but prepends 4555 to the AS_PATH as it does so. Suppose 9327's uses a transit provider which builds prefix filters from the IRR, and the "as9327" aut-num object is modified to include policy which suggests 9327 provides transit for 4555. Suppose this is not actually the case, though, and in fact 9327 is a rogue AS which is trying to capture 4555's traffic.
The rest of the world sees a prefix with an AS_PATH attribute which ends with "9327 4555".
In this case, from the point of view of those trying to discern legitimacy of advertisements, what is the origin of the prefix? Is it 4555, or 9327?
from BGP's perspective, you tell me. being the naive BGP listen/speaker - i think that AS 4555 is the origin. now... what does Prefix 198.32.6.0/24 say is the correct origin?
Is it possible to tell, from just the right-most entry in the AS_PATH attribute?
nope - but you have jumped right into the path question. (what does the as4555 aut-num object say about using 9327 as an upstream AS?)
Joe
[note: 9327 is not a rogue AS, in fact. This is just hypothetical :-)]
sez you :) (reminder to send Cingular the royalty check if you receive the above two characters ":" and ")" as listed above AND you chose to infer mood or intent.) I think -all- AS are run by rouges and pirates. -- (headless) bill