Mel, There was a Cisco bug many years ago that caused lots of issues. Since then we have limited max-as to 50 and it has not caused any reported issues yet.
Link that does not require a CCO login to view. http://blog.ipspace.net/2009/02/oversized-as-paths-cisco-ios-bug.html Regards Steve Lalonde > On 21 Jun 2017, at 16:49, Mel Beckman <m...@beckman.org> wrote: > > Steinar, > > What reason is there to filter them? They are not a significant fraction of > BGP paths. They cause no harm. It's just your sense of tidiness. > > You might consider contacting one of the operators to see if they do have a > good reason you haven't considered. But absent a good reason *to* filter > them, I would let BGP mechanics work as intended. > > -mel beckman > > On Jun 21, 2017, at 12:57 AM, "sth...@nethelp.no" <sth...@nethelp.no> wrote: > >>> Just wondering if anyone else saw this yesterday afternoon ? >>> >>> Jun 20 16:57:29:E:BGP: From Peer 38.X.X.X received Long AS_PATH=3D AS_SEQ(2= >>> ) 174 12956 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 234= >>> 56 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 23456 = >>> 23456 23456 23456 23456 23456 ... attribute length (567) More than configur= >>> ed MAXAS-LIMIT >> >> There are quite a few examples of people using stupidly long AS paths. >> For instance >> >> 177.23.232.0/24 *[BGP/170] 00:52:40, MED 0, localpref 105 >> AS path: 6939 16735 28163 28163 28163 28163 28163 28163 >> 28163 28163 28163 28163 28163 28163 28163 28163 28163 28163 262401 262401 >> 262401 262401 262401 262401 262401 262401 262401 262401 262401 262401 262401 >> 262401 262401 262401 262949 52938 52938 52938 52938 52938 52938 52938 52938 >> 52938 52938 52938 I >> >> I currently have 27 prefixes in my Internet routing table with 40 or >> more ASes in the AS path (show route aspath-regex ".{40,}"). >> >> I see no valid reason for such long AS paths. Time to update filters >> here. I'm tempted to set the cutoff at 30 - can anybody see a good >> reason to permit longer AS paths? >> >> Steinar Haug, Nethelp consulting, sth...@nethelp.no
