[21261] in North American Network Operators' Group
Re: Strange BGP announcement.
daemon@ATHENA.MIT.EDU (Brett Frankenberger)
Mon Nov 9 08:44:35 1998
From: Brett Frankenberger <brettf@netcom.com>
To: sgifford@alastair.tir.com (Scott Gifford)
Date: Mon, 9 Nov 1998 07:30:04 -0600 (CST)
Cc: nanog@merit.edu
In-Reply-To: <Pine.SOL.3.91.981109014319.8748B-100000@alastair.tir.com> from "Scott Gifford" at Nov 9, 98 01:48:27 am
:: Scott Gifford writes ::
>
> > > > Bays don't crash (at least not in the general case ... for example,
> > > > mine stayed up this time and the last time this happened), but they do
> > > > send a NOTIFY and bring down the BGP session, as required by the RFC.
> > > > (I believe gated does this also.)
>
> In case any Bay Networks users didn't already know this, reasonably new
> version of the system software have a switch to turn off this behavior:
>
> 1:TN]$g wfBgpPeerEntry.41.*
> wfBgpPeerEntry.wfBgpPeerASLoopDetect.157.130.101.182.157.130.101.181 = 2
> wfBgpPeerEntry.wfBgpPeerASLoopDetect.204.70.16.38.204.70.16.37 = 1
> wfBgpPeerEntry.wfBgpPeerASLoopDetect.204.70.100.66.204.70.100.65 = 1
> wfBgpPeerEntry.wfBgpPeerASLoopDetect.209.54.51.230.209.54.51.229 = 2
> wfBgpPeerEntry.wfBgpPeerASLoopDetect.209.54.101.238.209.54.101.237 = 2
>
> [1:TN]$set wfBgpPeerEntry.wfBgpPeerASLoopDetect.204.70.100.66.204.70.100.65 2
> (41) (interface)
> [1:TN]$commit
>
> Set this flag to '2' for each interface to keep your router from tearing
> down BGP sessions when it finds a loop. Don't forget to commit
> afterwards, and then to do a "save config config" so it will take after
> you reboot.
This wasn't a loop. This was a malformed AS path. The length of the
entire AS Path attribute was 14 bytes, and the length of the first AS
Sequence segment was 7 AS's, even though there wasn't room to fit that
many in 14 bytes. (7AS's * 2 bytes each + 2 bytes for the segment
header, gives a minimum of 16 bytes needed.)
Does this attribute also disable detection of malformed AS Paths?
- Brett (brettf@netcom.com)
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