UDP Error

General Beta 6.0
43

Same error here after upgrading from 5.x to latest 6.x as of posting. Log shows

2025-03-02 08:10:49.343 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:21:00.829 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:25:31.045 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:25:51.351 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:31:03.791 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:41:07.356 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:47:52.077 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:51:10.001 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)
2025-03-02 08:52:50.520 GMT [3723M] WARNING: Connection error (2001:4860:4860::8888#53): failed to send UDP request (Network unreachable)

I should add that other than that, the upgrade was smooth with no issues. Good job!

44

Tried that yet:

45

Running Pi-Hole in a docker container on a Synology NAS.
Same error, but only with IPv6 addresses.
Disabling IPv6 in Pi-Hole dns settings solves problem.

46

A I wrote above I run my pi-hole in an LXC container. My 2nd instance is configured as secondary DNS in Fritz!Box and not upgraded.

After I upgraded my primary DNS instance I see

image
image914×350 20.1 KB

and Fritz!Box is often using the secondary (pi-hole 5.x) instance. Before the upgrade my primary instance was often used cause less load.

I would sa, something is here broken.

47

As explained before, Network unreachable is likely due to lack of public IPv6 connectivity.
As it does not make sense to configure Pi-hole to use IPv6 servers, unticking them from Pi-hole's upstream is the logical thing to do, and would make those errors disappear.

As for Connection prematurely closed by remote server received from an unbound upstream, we've intensively analysed and identified that as being caused by specific behaviour of unbound, see Two Pi-hole instances, One with "failed to send..." - #44 by DL6ER.

There is currently nothing that Pi-hole could do to improve this.

The condition has been reported to unbound, where some potential measures are currently explored. Increasing unbound's incoming-num-tcp (e.g. to 20) is reported to mitigate the issue.

You may consider to contribute your observation over at failed to send TCP(read_write) packet (Connection prematurely closed by remote server) · Issue #1237 · NLnetLabs/unbound · GitHub.

For other cases involving encrypting upstream resolvers like cloudflared, we've seen reports that mIxEd case queries may trigger connection errors.
In such a case, it may help to set misc.dnsmasq_lines under Settings | All settings » Miscellaneous to contain no-0x20-encode.

For all other cases, sharing the upstream DNS servers as well as the full error message (including the root cause in brackets) may help identify an issue.

1 Like
49

I'm not running in Docker; is unticking IPv6 sensible when running on bare metal?

50

Hello
Upgraded to core 6.0.5 the other day.

Pi4B, bare metal, connected to the router via ethernet cable.

The pattern I see is like so:

2025-03-12 10:13:42.844 INFO Received 8/8 valid NTP replies from pool.ntp.org
2025-03-12 10:13:42.844 INFO Time offset: -1.155257e+00 ms (excluded 0 outliers)
2025-03-12 10:13:42.844 INFO Round-trip delay: 2.590346e+01 ms (excluded 0 outliers)
2025-03-12 10:21:08.495 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 10:31:22.234 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 10:42:06.059 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 10:52:40.437 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 11:02:50.438 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 11:12:59.582 WARNING Connection error (2620:fe::fe#53): failed to send UDP request (Network unreachable)
2025-03-12 11:13:43.150 INFO Received 8/8 valid NTP replies from pool.ntp.org
2025-03-12 11:13:43.150 INFO Time offset: 1.887287e+00 ms (excluded 1 outliers)
2025-03-12 11:13:43.151 INFO Round-trip delay: 3.280960e+01 ms (excluded 1 outliers)

Hope it helps

51

See my post above:

1 Like
52

Thanks, I think I got it now.

53

Yes, it was the fix. Thankyou. Just uncheck the IPv6 DNS Upstream and it will work correct.