DNSMASQ_WARN Warning

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1

The issue I am facing:
I get this message frequently for this IP address.
|2023-04-16 09:50:00|DNSMASQ_WARN|Warning in dnsmasq core:
disabling DHCP static address 192.168.168.137 for 10m|

Seems to always be same address, which I traced with MAC to a thermostat.

Details about my system:
PiHole running as ad blocker and DHCP server.

How can I troubleshoot this further to eliminate this message?

What I have changed since installing Pi-hole:
Nothing really, just making it DHCP server recently.

Debug log created.

Thanks, Carl

2

Can you run the debug log again please and post the tricorder URL it gives you. That will let staff find it on their secure system.

The docs advise that the thermostat returned a DHCPDECLINE message to the Pi-hole. This in turn implies that the thermostat sees the address offered as already in use.

The debug log will help reveal how your networking is set up and may shed some light on this.

1 Like
3

Sorry about that. I forgot to check the box for the tricorder URL, so I didn't see in the in the log last time.

https://tricorder.pi-hole.net/xILCUPoo/

Carl

4

You have two DHCP servers active, and they are passing out conflicting information:

*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
   Scanning all your interfaces for DHCP servers
   Timeout: 10 seconds
   
   WARN: Could not sendto() in send_dhcp_discover() (/__w/FTL/FTL/src/dhcp-discover.c:233): Network is unreachable
   * Received 326 bytes from eth0:192.168.168.1
     Offered IP address: 192.168.168.111
     Server IP address: 192.168.168.1
     Relay-agent IP address: N/A
     BOOTP server: ecosystem.home.cisco.com
     BOOTP file: (empty)
     DHCP options:
      Message type: DHCPOFFER (2)
      server-identifier: 192.168.168.1
      lease-time: 86400 ( 1d )
      renewal-time: 43200 ( 12h )
      rebinding-time: 75600 ( 21h )
      netmask: 255.255.255.0
      broadcast: 192.168.168.255
      domain-name: "hsd1.ma.comcast.net"
      hostname: "raspberrypi"
      dns-server: 192.168.168.1
      router: 192.168.168.1
      --- end of options ---
    
   * Received 302 bytes from eth0:192.168.168.111
     Offered IP address: 192.168.168.121
     Server IP address: 192.168.168.111
     Relay-agent IP address: N/A
     BOOTP server: (empty)
     BOOTP file: (empty)
     DHCP options:
      Message type: DHCPOFFER (2)
      server-identifier: 192.168.168.111
      lease-time: Infinite
      netmask: 255.255.255.0
      broadcast: 192.168.168.255
      dns-server: 192.168.168.111
      domain-name: "CSMNET"
      hostname: "RaspberryPi4"
      router: 192.168.168.1
      --- end of options ---
    
   DHCP packets received on interface eth0: 2
   DHCP packets received on interface lo: 0
   DHCP packets received on interface wlan0: 0
5

Thanks so much! Ugh... I left the Router DHCP enabled in error, and completely missed checking that. Can clearly see that in the log now, but I just wasn't looking for that, was more focused on the IP that was causing the issue. I was switching back and forth between the 2 DHCP's and forgot to disable that one last time. I am still troubleshooting another issue I have with OpenVPN that works with the router DHCP no problem, but not the Pi-Hole DHCP. Everything else is the same, just toggle the 2 DHCP's.

6

If you'd need those DHCP servers to coexist, then you should at least make sure that their respective DHCP ranges would not overlap. That would avoid your observation (unless you'd have some devices with static IPs configured on device).

Furthermore, for routers that can't disable DHCP, we usually recommend to restrict your router's DHCP range to accommodate just Pi-hole's host machine, and configure a DHCP lease reservation/fixed IP address for that in your router.

7

@Bucking_Horn Good advice. One thing I don’t quite understand though is if there are two ranges, how would it know for incoming assignment, which range to go with?

In my case I would run the router DHCP for just VPN since it doesn’t seem to be working on PiHole DHCP. MAC address for the client would be same, but on VPN coming through the tunnel, vs. local network.

Thanks, Carl

8

With multiple DHCP servers on the same network segment/link, a client would be free to accept any one DHCP offer at its own discretion. As soon as a client would accept one DHCP server's offer, all other DHCP servers would discard their respective previous offers.

Restricting your router's DHCP range to accommodate just Pi-hole's host machine would prevent clients from picking up a DHCP lease from your router (and thus potentially by-passing Pi-hole).

9

@Bucking_Horn Thanks for the info. Easy to understand now. Appreciate it.

Carl

10

@Bucking_Horn one more question. I was having trouble connecting a Blink Camera with the PiHole DHCP activated (linksys DHCP disabled). Then I disabled the PiHole DHCP, and made the Linksys DHCP active, and it connected. What should I look at further as to why the PiHole DHCP did not connect the camera but the Linksys DHCP did?

Carl

11

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