[nsd-users] Ignored IPv6 requests

[Stephane Bortzmeyer]

I switched a low-usage DNS server from NSD 3 to NSD 4 and I see now
that, from time to time, it stops serving IPv6 requests (timeout). The
problem seem to occur randomly, it lasts a few minutes, then cures
itself. Nothing similar for IPv4. (By the way, the -6 option of
-ex-Nagios monitoring plugins is broken, see 
<https://github.com/monitoring-plugins/monitoring-plugins/issues/1228>.)

It is not a network/L3 issue: when the problem happens, even a dig on
the name server to itself over the local interface fails. Also, with
tcpdump on the name server, I see DNS requests coming in but nothing
coming out.

strace on the daemon does not show a recvmmsg(sa_family=AF_INET6...)
for my address when tcpdump sees the packet coming in.

Could it be because of something else than NSD? At the same moment, I
switched to Linux kernel 3.12.6 on a Linode VPS. Any similar problems
with this setup? (If I have time, I will try with Knot, to compare and
to see if it's the fault of the kernel.)