TCP Maximum Segment Size tuning. The TCP path MTU discovery protocol option is enabled by default in AIX. This option allows the protocol stack to determine the minimum MTU size on any network that is currently in the path between two hosts, and is controlled.
![Tcp Tcp](https://developer.ibm.com/developer/articles/au-aix7networkoptimize3/images/fig01.jpg)
We have an AIX box, running what we call in banking 'ATM Switch' not the ATM networking switch, but the bank ATM driver.