IPv6 configuration of AIX

How can I enable IPv6 on AIX?

You should traverse several menu in smit(graphical)/smitty(curses) tool.

Enable Autoconfiguration

 Communications Applications and Services ->
  TCP/IP                                   ->
  IPV6 Configuration                       ->
  IPV6 Daemon/Process Configuration        ->
  Autoconf6 Process                        ->
  Start Using the Autoconf6 Process        ->
  BOTH Now and at System Restart

Enable Neighbor-Discovery

 Communications Applications and Services ->
  TCP/IP                                   ->
  IPV6 Configuration                       ->
  IPV6 Daemon/Process Configuration        ->
  Ndpd-host Subsystem                      ->
  Start Using the Ndpd-host Subsystem      ->
  BOTH Now and at System Restart

Do I have to configure/restart inetd also to provide IPv6 via internet superserver?

In theory you should configure inetd to have IPv6 also, but in practice (since AIX using dual-stack technology) you can use IPv6 service after enabling IPv6 as described in earlier section.

There is some IPv6 conectivity problem with AIX box. What to do?

Symptoms : I can reach machines on the LAN via IPv6 (e.g. with ping), but remote machines canoot reach me via IPv6 (e.g. no answer to ping).

Very likely that ndpd-host process is not running. Enable it as described in earlier sections.

Configuring IPv6 applications on AIX