How do I setup jumbo frames under IBM AIX operating systems using command line tools?
You can use any one of the following method.
Method #1: Use SMIT Tool
The AIX comes with a tool called "SYSTEM Management Interface Tool" (SMIT), It is an interactive tool bundled with AIX which provides a menu-based alternative to the command line for managing and maintaining the AIX operating system. This tool can be used to setup jumbo frames too.
You need to go to Devices > Communication > Ethernet Adapter > Adapter > Change / Show Characteristics of an Ethernet Adapter > Select the interface in question from the list (such as ent1 or ent2). Make sure you enable jumbo frames.
Change/Show Characteristics of an Ethernet Adapter Type or select values in entry fields. Press Enter AFTER making all desired changes. [Entry Fields] Ethernet Adapter ent0 Description 10/100/1000 Base-TX PCI-X Adapter (14106905) Status Available Location 1H-08 Receive descriptor queue size  +# Transmit descriptor queue size  +# Software transmit queue size  +# Transmit jumbo frames yes + Enable hardware transmit TCP resegmentation yes + Enable hardware transmit and receive checksum yes + Media Speed Auto_Negotiation + Enable ALTERNATE ETHERNET address no + ALTERNATE ETHERNET address [0x000000000000] + Apply change to DATABASE only no + F1=Help F2=Refresh F3=Cancel F4=List Esc+5=Reset Esc+6=Command Esc+7=Edit Esc+8=Image Esc+9=Shell Esc+0=Exit Enter=Do
How do I Set MTU to 9000 under AIX operating systems?
Next, hit F3 key (or [esc]+3) and come back to the System management main menu. Go to TCP/IP item. Find MTU and set it to 9000.
Option #2: Command Line Option To Change MTU under AIX UNIX
In this example I'm setting mtu to 9000 for ent1/en1
chdev -Pl ent1 -a jumbo_frames=yes chdev -Pl en1 -a mtu=9000
You need to reboot the server. Please note that both smit/smitty or the chdev command changes the values in the ODM database on disk so they will be permanent. Please note that the following command will only work over the ssh session if use a different interface for ssh'ing in to the server:
chdev -P -l ent1 -a media_speed=Auto_Negotiation ifconfig en1 down detach chdev -l ent1 -a jumbo_frames=yes chdev -l en1 -a mtu=9000 chdev -l en1 -a state=up