DHCP not working with "Too few arguments" error log

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22

Something is wrong with this rule from OpenHAB manual:

iptables -A PREROUTING -t mangle -p udp ! -s 127.0.0.1 --dport 67 -j TEE --gateway 127.0.0.1

As soon as this is active (and one request comes in) /var/log/pihole.log is flooded with entries like this and CPU usage jumps through the ceiling:

Jul 12 01:06:44 dnsmasq-dhcp[13323]: DHCPREQUEST(lo) 192.168.0.XX CL:IE:NT:MA:CA:DR
Jul 12 01:06:44 dnsmasq-dhcp[13323]: DHCPACK(lo) 192.168.0.XX CL:IE:NT:MA:CA:DR client-hostname

Normal lookup without iptables rule looks like this:

Jul 12 01:06:44 dnsmasq-dhcp[13323]: DHCPREQUEST(eth0) 192.168.0.XX CL:IE:NT:MA:CA:DR
Jul 12 01:06:44 dnsmasq-dhcp[13323]: DHCPACK(eth0) 192.168.0.XX CL:IE:NT:MA:CA:DR client-hostname

23

These requests are coming on your loopback (lo) (127.0.0.1) . I don't know why OpenHab is requesting so many or what's the reason behind OpenHab needing this in the first place (Me and OpenHab = 0 history) ...

This is a normal request originating from the interface FTLDNS is listening on (eth0).

24

No it's not OpenHAB (it isn't running) -- it's the iptables rule that somehow copies and edits that packet, and then goes crazy. There are some thousand requests per second (from some minutes of testing until I wondered about missing responsiveness of my Pi I have 800 MiB of log file...). It stops as soon as I delete the rule.

I have to look that up tomorrow, I will really go to bed now.

25

It might be the PREROUTING that causes the spike.

here's why:

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