Traffic dodging pihole DNS

Running pihole on a Raspberry Pi 3b+. DHCP is my router, a Motorola MG7550, which has the primary DNS set to my pihole (192.168.0.69), secondary DNS 0.0.0.0, and ipv6 disabled.

When setting up, everything works as expected for a few hours, then suddenly only queries from my desktop make it to the pihole (Windows machine, which has the DNS set to the pihole in my ethernet adapter settings), and I don't think all of my traffic from it is even going to the pihole. Laptop (MacOS) and mobile (android) aren't showing up in the log at all and aren't having ads blocked.

Windows desktop nslookup pi.hole output:

Server:  pi.hole
Address:  192.168.0.69

Name:    pi.hole
Addresses:  fe80::a524:7487:e346:c762
          192.168.0.69

MacOS laptop nslookup pi.hole output:

Server:		75.75.75.75
Address:	75.75.75.75#53

** server can't find pi.hole: NXDOMAIN

75.75.75.75 is a Comcast DNS.

Expected Behaviour:

  1. I expect I should be able to access pi.hole/admin from all devices, but I can only do so on my desktop
  2. I expect queries from all devices in the query log
  3. DNS from debug output should be pi-hole address 192.168.0.69

Actual Behaviour:

  1. On my laptop, I can only access the pihole dashboard by navigating directly to the IP address (192.168.0.69/admin)
  2. No queries from other devices, and I'm not sure if all of my desktop queries are going through either (despite DNS set manually to pi-hole)
  3. DNS from debug output are 75.75.75.75 and 75.75.76.76 (both Comcast)

Debug Token:

https://tricorder.pi-hole.net/eHqT4NO5/

Any help would be appreciated. Thanks!

Your debug log shows the router is advertising 75.75.75.75 and 75.75.76.76 as DNS servers:

*** [ DIAGNOSING ]: Discovering active DHCP servers (takes 10 seconds)
   Scanning all your interfaces for DHCP servers
   Timeout: 10 seconds
   
   * Received 321 bytes from eth0:192.168.0.1
     Offered IP address: 192.168.0.69
      (...)
      dns-server: 75.75.75.75
      dns-server: 75.75.76.76

Where exactly did you set Pi-hole as DNS server?

I don't know Motorola MG7550 routers, but most routers have 2 places to configure DNS servers:

  • DHCP/LAN settings (the names can vary depending on the brand/model) - this is the preferred place to set Pi-hole.
    The information above shows your router has 75.75.75.75 and 75.75.76.76 set in the DHCP settings.
    I'm not sure if your router has an option to change that;

  • WAN/Internet settings (if you set Pi-hole here, your router will be the only device showing on the Dashboard).

Yeah, the 75.75.75.75 and 75.75.76.76 are definitely Comcast, and shouldn't be there. The DNS for the router is set under Advanced > Status > Connection > IPv4 DNS Servers (screenshot below with Help text). The DHCP settings really just has whether or not the DHCP server is activated (yes), the local address pool + lease time, then clients and setting static IPs.

In this case, you have the alternative to disable the DHCP on your router and use Pi-hole as DHCP server.

You can also manually configure each individual device to use Pi-hole IP as DNS server, but this is usually the last alternative.

I was hoping to avoid going that extra step by finding out how / why my router is inserting some other DNS in, or finding some mistake I've made, but maybe I don't have a choice. I definitely want to avoid manually configuring each device, as I would like my partner's devices and my Android streaming box to easily utilize the pi-hole as well.

I will work on setting the pi-hole as the DHCP server then, and see if that fixes the problem. Thanks!

This reddit post is for a different Xfinity MD model but its the same issue. The DNS settings can be made to work for a while but then just reverts back.

The DNS settings can be made to work for a while but then just reverts back.

Yeah, I bet that's what's going on here.

I actually didn't realize how dead simple it was to switch the pi-hole to being my DHCP server. So far, it seems to have worked - all devices are blocking ads as expected, and I can access the admin portal properly (thru pi.hole/admin). Thanks!

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