MikroTik strikes again ?
%BGP-6-ASPATH: Long AS path ... 39412 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
39625 39625 39625 39625 received from xxxx: More than configured
MAXAS-LIMIT
aut-num: AS39625
as-name: ARANEO-AS
descr: Omni-Araneo's AS number
org: ORG-OSTW3-RIPE
import: from AS12968 action pref=100; accept ANY
export: to AS12968 announce AS39625
import: from AS39412 action pref=100; accept ANY
export: to AS39412 announce AS39625
admin-c: TW1273-RIPE
tech-c: TW1273-RIPE
mnt-by: AS12968-MNT
mnt-routes: AS12968-MNT
source: RIPE # Filtered
Uhm....okay...but why does anyone prepend their ASN that much? Are you saying the Mikrotik did that on purpose?
Adrian M wrote:
Adrian M wrote:
> MikroTik strikes again ?
>
> %BGP-6-ASPATH: Long AS path ... 39412 39625 39625 39625 39625 39625
> 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
From: Bret Clark [mailto:bclark@spectraaccess.com]
Sent: Monday, 3 May 2010 8:26 PM
To: nanog@nanog.org
Subject: Re: MikroTik strikes again ?
Uhm....okay...but why does anyone prepend their ASN that much? Are you
saying the Mikrotik did that on purpose?
MikroTik asks for an amount of prepends rather than what ASN to prepend
with.
There was a bug in an old version that would modulus the ASN with 256 and
prepend that many times.
In this case 39625 modulo 256 = 201 prepends.
It's not really a bug, only a matter of habbit I guess 
I read this some time ago in nanog list:
http://www.renesys.com/blog/2009/02/longer-is-not-better.shtml
regards,
Christian
Bret Clark wrote:
Tim Warnock wrote:
Adrian M wrote:
MikroTik strikes again ?
%BGP-6-ASPATH: Long AS path ... 39412 39625 39625 39625 39625 39625
39625 39625 39625 39625 39625 39625 39625 39625 39625 39625 39625
From: Bret Clark [mailto:bclark@spectraaccess.com]
Sent: Monday, 3 May 2010 8:26 PM
To: nanog@nanog.org
Subject: Re: MikroTik strikes again ?
Uhm....okay...but why does anyone prepend their ASN that much? Are you
saying the Mikrotik did that on purpose?
MikroTik asks for an amount of prepends rather than what ASN to prepend
with.
There was a bug in an old version that would modulus the ASN with 256 and
prepend that many times.
In this case 39625 modulo 256 = 201 prepends.
Yeah...guess I see why that would be a problem.
There was a well-known routing incident last year in which a difference
between the Mikrotik and Cisco CLIs caused the propagation of extremely long
AS-PATH attributes, which caused certain Cisco routers to crash.
Basically, someone remembered their Cisco IOS syntax and typed "bgp-prepend
47868" into a Mikrotik; the correct syntax would have been "bgp-prepend x
47868" where x is an integer between 0 and 16 representing the desired number
of prepends. The Mikrotik correctly tried to prepend 47868 47868 times, but
had only one byte to store this value and therefore produced 255 prepends.
Some Cisco machines, it turned out, had a bug that caused path lengths close
to 255 to crash them. Fun and games ensued.
The Renesys blog has much, much more:
http://www.renesys.com/blog/2009/02/longer-is-not-better.shtml