AS path question.

Stefan Fouant sfouant at
Wed Nov 10 14:53:59 CST 2010

> -----Original Message-----
> From: Greg Whynott [mailto:Greg.Whynott at]
> Sent: Wednesday, November 10, 2010 3:40 PM
> To: nick at
> Cc: nanog at
> Subject: Re: AS path question.
> thanks all,  this makes sense now.    and i just showed the internet
> how ignorant I am.

No such thing!  We are all here to learn, and so there are no such things as
stupid questions IMO.  I certainly won't rail you for asking a question like
that... ahem, Neils Bakker might so there are no guarantees ;)

> i have my maxas-limit set to 10 based on an article I was reading.
> perhaps I should up that a bit.

I think 10 is way too short.  I would definitely up that.

> what sort of problems are associated to overly long AS paths?   is it
> more of a system resource control setting?

I remember back in 1999 at UUnet we had a bug in IOS in which some AS Paths
were supposedly being prepended well above 255 AS Paths... IIRC that is
above the maximum field length (I'd have to dig it up to be sure though) and
it was actually causing routers to crash as they were interpreting the BGP
messages as malformed.  Today we have better protections in IOS preventing
this and other associated "buffer overflow" issues, but at the time there
were no such protections.  The very next day we received a patched IOS from
Cisco which contained the maxas-limit commands.

Stefan Fouant

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