[afnog] A heads up on a nasty IPv6 bug

[Andrew Alston]

Hi Guys,

Figured I’d share this because someone might run into the issue I did last night and after how long it took to figure out what was going on, rather give people a heads up.

Under Cisco IOS-XR 5.3.3 AND under 6.0.2 (though the documentation on the bug explicitly states its fixed in 6.0.2, its NOT), do not, under any circumstances, run ipv6 nd router-preference high anywhere.

That particular command has an extremely high chance of crashing your IPv6_nd process on the box, and when that process goes down, things get pretty strange.  For a while, the box will seem to be working ok, but as the neighbors expire, things go from bad to worse.  We noticed that the first thing we lost is the point to point connectivity across the interface.  Weirdly, going THROUGH the interface would keep working for anywhere from 15 to 30 minutes, then that would die as well, and a little while later, if you are running ISIS in single-topology mode as we do, ISIS would fall over as well.

Once you get that process crash, restarting the process also doesn’t seem to clean up whatever else went wrong, and the ONLY resolution at that point that we could find was a complete restart of the box.

We replicated this behavior on fully patched 5.3.3 and on XR 6.0.2.

Removal of the command and then a reboot of the box ensuring it’s not there anymore fixes the problem.

Thanks

Andrew

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