Long AS Path

sthaug at nethelp.no sthaug at nethelp.no
Wed Jun 21 07:56:26 CST 2017


> 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, sthaug at nethelp.no


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