DNS name server, IPv6 and hang of listener

The other day during an operation on one of the DNS servers, some of our RAC listeners went down and stop responding.

We found this happened when they brought down one of the DNS name servers, even thought one was up and running.

Ping, ssh and so on was working fine. But any operation with ‘lsnrctl’ or ‘srvctl xxx listener’ would hang.

After investigation together with the system administrator it was found that it was related to the IPv6 lookups which are activated by default on AIX and are done when the first IPv4 lookup fails.

To solve the problem was just necessary to disable the IPv6 lookups by changing the /etc/netsvc.conf file to:

This is explained on this IBM note.