3 Networky AIX 6/7 gotchas....

A colleague came across this tricky gotcha in AIX7 - his scp sessions were stalling on AIX 7.1 (VIO client) LPARs.

There is not much on the net about this one yet

By disabling tcp timestamp randomisation feature on both source and target VIO clients the randomised timestamp value is not used for setting the retransmission timer

Fix

 #no -o tcp_rand_timestamp=1

Here is the APAR http://www-01.ibm.com/support/docview.wss?uid=isg1IV13121 IV13121: TCP RETRANSMIT PROCESSING IS VERY SLOW.

One possible cause of an SEA on VIOS flip flopping from primary to backup is processor unfolding delays http://www-01.ibm.com/support/docview.wss?uid=isg3T1012941

Fix - stop folding
# schedo -p -o vpm_fold_policy=4

There is a fair bit on the net about this one...

Another one I'll put here (AIX 6/7 and Oracle 11g network stalling/delays)
With Oracle 11g came IPv6 support and even though a hostname may be resolved in IPv4 land a second lookup into /etc/hosts is done for the IPv6 address/hostname.

If the IPv6 address is not matched in /etc/hosts then it goes out to the DNS servers for IPv6 name resolution because of the (default) name resolution order in net service (/etc/netsvc.conf) was local then bind
Fix
Force the IPv4 ie in /etc/netsvc.conf change local, bind to local4, bind4

There is a LOT on the net about this one....