I've seen something like this a few times, mostly on servers with
HACMP (redundant NICs in failover config).
For reason I can only guess, AIX routing table redirected outbound
traffic to 127.0.0.1. Only connection within the same subnet worked
OK.

Once I disabled PMTU discovery and manually corrected routing table,
outbound connections started working fine.
Apparently, PMTU discovery dynamically updates AIX routing table with
optimized paths to specific hosts - and sometimes makes a mistake.

How to check and disable PMTU discovery:
no -a | grep pmtu
grep pmtu /etc/tunables/lastboot

no -p -o udp_pmtu_discover=0
no -p -o tcp_pmtu_discover=0

no -a | grep pmtu
grep ptmu /etc/tunables/nextboot

Hope this will help.


Regards,
brother Matthius