Unable to find any PTR-records for the specified domain/ip :(
Log
+000
Resolving PTR record of '2600:9000:21ac::'
+161
ERRNo PTR record availible DNS server 'pdns1.ultradns.net' raised an NotExistentDomain error, while beeing queried for PTR-records on domain '0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.c.a.1.2.0.0.0.9.0.0.6.2.ip6.arpa'.