AS PATH limits

William Herrin bill at
Sun Oct 1 05:24:46 CST 2017

On Sun, Oct 1, 2017 at 1:05 AM, Ken Chase <math at> wrote:

> I don't quite understand the exact situation that causes the issue - our
> cogent facing router (quagga .99.22 debian) was receiving the route but
> that
> session stayed up - it was it while sending or the other igp router (also
> quagga .99.22) receiving (I think the latter) that was crashing their
> session.
> Not quite sure why the cogent session didn't crash as well (or first,
> before
> propagating the bad route).

Hi Ken,

Technically the route is not bad, just really inconsiderate.

The bug happens when quagga sends the the long-AS path route to a peer. As
I understand it, when the announcement is larger than one segment, Quagga
double-counts the some of the bytes when computing the number of bytes in
the AS path. It receives the announcement just fine, but then it corrupts
what it sends to the neighbor who then chokes.

Bug and patch here:

Bill Herrin

William Herrin ................ herrin at  bill at
Dirtside Systems ......... Web: <>

More information about the NANOG mailing list