IPv6 BGP & kernel 4.19

Benedikt Neuffer benedikt.neuffer at kit.edu
Thu Jun 20 18:13:43 CEST 2019


On 19.06.19 20:09, Alarig Le Lay wrote:
> Hi,
> On mer. 19 juin 09:10:53 2019, Robert Sander wrote:
>> Hi,
>> our routers run on Debian stretch with bird 1.6.4 from
>> bird.network.cz/debian.
>> Yesterday I tried kernel 4.19 from backports.debian.org and ran into a
>> weird issue with IPv6 BGP sessions:
>> All Peerings reported "Error: Hold timer expired" ca. every 40 minutes.
>> IPv6 forwarding was flapping all the time.
>> After rebooting into kernel 4.9 everything worked again.
>> IPv4 BGP was not affected and also OSPF (v4 and v6). I could disable all
>> IPv6 BGP peerings on this router and then it forwarded to another router
>> learned via OSPF for IPv6 without issues.
>> Has anyone seen such a behaviour?
> I’ve seen this with 4.19 on gentoo. For now I’m still running 4.14.
> https://archives.gentoo.org/gentoo-user/message/fab628cc53e4a55589410f9dff6abd23

Same here. Gentoo, Linux 4.19.52, Bird 2.0.4. I am running a full table
using a separate VRF and the default table as management VRF.

Without traffic through the box (all IPv6 prefixes filtered) the bgp
sessions is stable. With traffic the bgp session dies after some time
and ssh connections in the default table freezes.

I did some packet captures and saw tcp retransmissions before hold timer

Kernel 4.14.127 is here stable, too. Sadly I have no time for a kernel
bisect until September. (And no glue where to start and how to trigger
the bug faster.)


Karlsruher Institute of Technology (KIT)
Steinbuch Centre for Computing (SCC)

Benedikt Neuffer
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