This post just as a follow-up for thread http://www.unix.com/aix/115548-hacmp-5-4-aix-5300-10-not-working.html: there was a bug in the clcomdES that would cause the Two-Node-Cluster-Configuration-Assistant to fail even with a correct TCP/IP adapter setup. That affected HACMP 5.4.1 in combinatin with (at least) AIX 5.3 from TL6 to TL12 (did not try older oslevels but found a post that could imply the problem did not exist at and below TL5) and RSCT 2.4.13.0
Problem with HACMP 5.4.1 shows as
Configuring cluster topology.
ERROR: Unable to use communication interface 'xxxxxxxxxx'.
For each of the above invalid communication interfaces listed,
please check that the owning node is running the clcomdES subsystem,
and that the /usr/es/sbin/cluster/etc/rhosts file is properly configured.
Also, check /var/hacmp/clcomd/clcomd.log logfile on remote node for possible errors.
[...]
Using an empty or a manually edited cluster rhosts does not make any difference but leads to the same error.
Now, this is fixed with (at least) SP10 for HACMP 5.4.1 (did not try older HA Service Packs). I could not find an APAR with a suitable description. Maybe it was related to IZ70306: CLCOMD HACMPNETWORK MALLOC MEMORY LEAK CAUSES CLCOMDES FAILURES which dates to 2010-09-06. I am not sure about that as during my tests I never saw the 5901 ODM error mentioned in the description but it also says that the clcomdES dies after "few verification invocations" and there are verification checks during Assistant run and the bug caused an incomplete cluster rhosts setup which led me to identify clcomdES as the culprit.