Thanks, A further question, is it mandatory for all the aggregated information be appended at the AS path, is it possible for some aggregations do not propagate outside? By this, I mean some ASes completely conceal their aggregated ASes when propagation.
thanks a lot. On Wed, Oct 22, 2008 at 10:31 PM, Ricardo Oliveira <[EMAIL PROTECTED]> wrote: > the ASes in the AS_SET resulted from merging 2 or more AS_PATHS, you only > know at least one of them is connected to AS3 ... > more details at rfc4271: > http://www.ietf.org/rfc/rfc4271.txt > > "An AS_SET implies that the destinations listed in the NLRI can > be reached through paths that traverse at least some of the > constituent autonomous systems. AS_SETs provide sufficient > information to avoid routing information looping; however, > their use may prune potentially feasible paths because such > paths are no longer listed individually in the form of > AS_SEQUENCEs. In practice, this is not likely to be a problem > because once an IP packet arrives at the edge of a group of > autonomous systems, the BGP speaker is likely to have more > detailed path information and can distinguish individual paths > from destinations. > " > > --Ricardo > > On Oct 22, 2008, at 8:17 PM, Kai Chen wrote: > >> Hi, >> >> I observe some BGP AS paths collected from Routeview having the AS-set >> in the last hop. According to my understanding, this is BGP route >> aggregation. However, my question is as follows: >> Suppose, there is a path AS1 AS2 AS3 {AS4 AS5 AS6}, how AS4 AS5 AS6 >> connect to AS3? >> Does it necessarily mean that AS4 AS5 AS6 are direct neighbors of AS4, >> and AS4 aggregate the routes from AS4 AS5 AS6 then exporting outside. >> or, it could be other cases such as AS4 aggregate AS5 AS6 first, and >> then AS3 aggregate AS4? >> >> Thanks in advance, > >
