Cache behavior with whoami.cloudflare.com

Hello, I would like to report a strange behavior:

I am running two computers on the same network:

  • Computer A is connected to the internet through a VPN.
  • Computer B connected to the internet without using a VPN.

On both computers:

  • stop any DNS proxy/resolver (no DNS queries are available)
  • run: watch -n 0.1 'dig -4 TXT whoami.cloudflare.com @173.245.58.100'

Result:

  • On computer A, ip address returned is sometimes his ip and sometimes computer B ip (VPN ip).
  • On computer B, ip address returned is sometimes his ip and sometimes computer A ip.

Computer B never had any access to the VPN.

Using another whoami service:

  • watch -n 0.1 'dig -4 ANY myip.opendns.com @208.67.222.222'

Result:
Opendns is always returning the ip address corresponding to the computer.

173.245.58.100 = ns1.cloudflare.com
208.67.222.222 = resolver1.opendns.com

I’m not a DNS expert therefore I cannot explain this behavior but it seems whoami.cloudflare.com is messing with DNS queries.
Thank you.

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