Why do I get this warning related to DNS packet sizes on Digital Ocean with IPv6?
At the moment, I have a DNS master being served from my Gandi VPS and slaves operated by friends at Linode. I just set up a new VPS to test as a slave at Digital Ocean, but when I run this DNSSEC test,
I get this warning for any queries directed to the IPv6 address of the Digital Ocean VPS:
No response was received until the UDP payload size was decreased, indicating that the server might be attempting to send a payload that exceeds the path maximum transmission unit (PMTU) size. (2604:a880:2:d0::826:6001, UDP_0_EDNS0_32768_4096)
(This address "2604:a880:2:d0::826:6001" is for the IPv6 side of my D.O. VPS. This warning does not appear for any of the Linode or Gandi systems, which are using both IPv4 and IPv6.)
I do run a firewall (ufw), but I get the same warnings regardless of disabling or enabling the firewall.