One of the root name servers we run recently lost IPv6 connectivity. Its logs then showed this: ``` 2019-04-17T10:23:09 warning: [.] refresh, outgoing, IPv6-master1@53: fallback to AXFR 2019-04-17T10:23:15 warning: [.] refresh, outgoing, IPv6-master2@53: fallback to AXFR 2019-04-17T10:23:19 info: [.] refresh, outgoing, IPv4-master1@53: remote serial 2019041700, zone is up-to-date ``` I've redacted the IP addresses in the above log. What you see is that Knot tried to refresh the zone over IPv6 first, and timed out, and eventually managed to refresh over IPv4. But the message it emitted, "fallback to AXFR", looks strange. I would have expected something like "timed out" or "unreachable" or something like that.