Re: Intermittent IPv6 connectivity on VPS

[z411 <z411%omaera.org@localhost>]

Update: It seems the issue is related to the network, not NetBSD at all.

After trying more in the Debian Linux machine, it seems to also drop
IPv6 connectivity intermittently.
`ip -6 neigh show` (its ndp -a equivalent) shows the following:

2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router STALE
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router DELAY
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router DELAY
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router PROBE
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router PROBE
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router PROBE
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router PROBE
2a06:a880:3::1 dev eth0 router FAILED
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router FAILED
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router FAILED
2a06:a880:3::1 dev eth0 router FAILED
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 router INCOMPLETE
2a06:a880:3::1 dev eth0 lladdr 0c:59:9c:8c:dc:e4 router REACHABLE

It's also having trouble resolving the gateway through NDP after the
entry gets stale, and the connection drops meanwhile.

So it's having the exact same behavior, although Linux seems to be more
lenient and it seems to retry more before expiring the NDP entry. I'm
mimicking this behavior on NetBSD through the following tunables:

net.inet6.icmp6.nd6_mmaxtries=15
net.inet6.icmp6.nd6_umaxtries=15
net.inet6.icmp6.nd6_delay=30
net.inet6.icmp6.nd6_prune=3600

It's a lot closer to Linux now, but it doesn't fix the problem - if
there's no IPv6 traffic for a while, it will have to probe for the
gateway again, which takes around 30-120 seconds of retries, which is
unacceptable for services. These tunables let me at least keep an
outgoing ping to keep the NDP entry alive, but that's janky.

I'm bringing the issue to the provider. If I show them Linux is having
the same issue I'm sure they'll listen this time.

Thanks to the people who took a look!