Seemingly random unexpected DNS settings (and a possible solution)

#1

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Expected Behaviour:

All sites on blocklist are unreachable. All DNS requests go through pihole. http://www.whatsmydnsserver.com/ only shows Cloudflare DNS servers (as these are what I selected during setup.)

Actual Behaviour:

Some sites on blocklist are reachable seemingly at random. http://www.whatsmydnsserver.com/ is sometimes showing my ISP DNS server is being used instead of Cloudflare.

Debug Token:

txn6nmycd1!

This was driving me nuts for several days!

I have an XB6 cable modem from my ISP (Shaw Cable) and a D-Link DIR-867 router connected to it. The pihole is running on a Raspberry Pi Zero W on the D-Link network. All devices are connected to the D-Link, with none connected directly to the XB6.

Sometimes sites that I know should be blocked would show up. When I checked on whatsmydnsserver.com it would sometimes show the Shaw (ISP) DNS servers either instead of or in addition to the Cloudflare servers.

What appears to be happening is the the D-Link router was using the IPv6 DNS settings, even though I don’t have an IPv6 service (my ISP doesn’t offer IPv6 services, but it appears that they are using IPv6 for management of the XB6 - the IPv6 gateway and DNS servers are defined, but there is not IPv6 WAN address that I can use.)

http://ipv6-test.com/ shows that “DNS6 + IP4” for DNS is enabled for my connection, so it seems to me like even though I don’t have an IPv6 WAN address, the D-Link can still query the IPv6 DNS server for an IPv4 address.

To fix this I disabled external IPv6 on the D-Link (set the IPv6 network type to “Local Connectivity Only” on the Settings >> Internet >> IPv6 page, and now everything works as I expect. It looks like all DNS requests are going to the pihole, and whatsmydnsserver.com only shows Cloudflare servers.

I wasn’t able to find any details on anyone else running into or fixing this problem, so I thought I should throw up a quick post summarizing it.

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#2

https://test-ipv6.com/ Works better for IPv6 testing

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#3

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assigned DanSchaper #4
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unassigned DanSchaper #5
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closed #7

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