Received invalid NTP request: not from an NTP client, ignoring

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1

How can I find out / debug what's going on exactly? Which device/IP/MAC is causing this?

Expected Behaviour:

More information on whats going on, what is wrong, which device is causing this, ...

Actual Behaviour:

Im getting the warning WARNING: Received invalid NTP request: not from an NTP client, ignoring many times in the log. Probably by this code line: FTL/src/ntp/server.c at 71b6fc62571075740a3c721d5e961db9c3609376 · pi-hole/FTL · GitHub.

2

Enable NTP debugging with below:

sudo pihole-FTL --config debug.ntp true

And tail/follow the logs live with below:

sudo tail -F /var/log/pihole/FTL.log

Or browse the logs with below to inspect:

sudo less /var/log/pihole/FTL.log

Can correlate timestamps from the warnings with those in the logs.
When finished diagnosing, flip it off again with below:

sudo pihole-FTL --config debug.ntp false

EDIT: You can also inspect NTP packets live with below for more details:

sudo tcpdump -nvvvi any udp port 123

The tcpdump binary is contained in the tcpdump package (for APT based distros):

sudo apt install tcpdump

And the pihole-FTL binary can also be used as an NTP client for diagnosing:

pihole-FTL ntp <NTP_SERVER_IP>

3

Thanks for that information. With that I found out, that it's a single device which is causing this: our Segway Navimow i105e. It's sending requests like the following:

16:12:34.144411 eth0  In  IP (tos 0x0, ttl 64, id 61520, offset 0, flags [DF], proto UDP (17), length 76)
    192.168.179.174.43579 > 192.168.178.55.123: [udp sum ok] NTPv1, unspecified, length 48
        Leap indicator:  (0), Stratum 0 (unspecified), poll 0 (1s), precision 0
        Root Delay: 0.000000, Root dispersion: 0.000000, Reference-ID: (unspec)
          Reference Timestamp:  0.000000000
          Originator Timestamp: 0.000000000
          Receive Timestamp:    0.000000000
          Transmit Timestamp:   0.000000000
            Originator - Receive Timestamp:  0.000000000
            Originator - Transmit Timestamp: 0.000000000

I notice that this request is detected as NTPv1, unspecified, while other, valid requests are detected as NTPv3, Client or NTPv4, Client.

I don't think I can do anything because the Navimow is just sending bad data, right?

4

It's probably some faulty time synchronization code it's running, likely part of whatever software they purchased and never fully enabled or disabled it.

Unless there are options in their app relating to time synchronization or NTP you are most likely out of luck in the short term.

I am not familiar with the vendor in question, but it may be worth reporting the issue to them for future fix via firmware upgrade.

In my experience the vast majority of IoT vendors completely ignore such reports, but I've had a few successes over the years.

5

Makes me wonder if FTL supports NTPv1 as NTPv4 is the latest.
@DL6ER , can you shed some light please if you read this?