Created attachment 1430339 [details]
Description of problem:
Since upgrading from F27 to F28 it seems that NetworkManager will initially configure IPv6 successfully but after a while (precise delay ranges from minutes to hours) it will seeming spontaneously delete the default IPv6 route.
I'm attaching the journal entries, with all domains set to level trace, starting from a restart of NetworkManager.
At 20:50:11 is successfully completes neighbour discovery with fe80::28ef:1dff:fe15:2fad as gateway and installs a default route using that gateway.
At 22:07:30 it reports a change of neighbour discovery configuration, with the change seemingly being that it has removed the gateway, as a result of which it removes the default route.
I can't see any indication of why it thinks the gateway has gone away though - it seems to have just decided that spontaneously!
Version-Release number of selected component (if applicable):
it looks like the router advertisement contained a gateway with zero lifetime and therefore NM dropped the route.
Can you please capture ICMPv6 packets with the following command (as root), wait that the problem happens again and attach the generated file?
tcpdump -i wlp58s0 -s 65535 -w icmp6.pcap icmp6
Created attachment 1430804 [details]
So I just had it happen again, logged at 18:35:16 in the journal and the packet capture is attached.
There are no RA packets at all though, only neighbour discovery requests and replies.
Right so I think the issue is that the gate is expiring because it's not seeing the periodic RAs.
Tracing the interface on the gateway I can see it sending them but them never seem to appear on the interface at the client!
There is some discussion about dropped ICMPv6 packets in bug 1575431. Can you try the workaround suggested at:
(i.e. disable ipv6 rp_filter and restart the firewalld service)?
I certainly agree that it seems to be an issue of ICMPv6 packets getting lost and I've been continuing to pursue this - at one point it seemed that reverting the other end of the link to an older kernel had fixed it but that turned out not to be the case.
I think I even tried stopping firewalld at one point - this machine is the only one I use that on which might be why I haven't seen this anywhere else. Of course if it had changed the kernel's rp_filter setting and didn't reset it on shutdown then just stopping it wouldn't be effective.
I will investigate further tonight...
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