Re: Long AS Path

[Steve Lalonde <steve () enta net>]

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 <mel () 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, "sthaug () nethelp no" <sthaug () 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, sthaug () nethelp no