AIX UNIX: Enabling Jumbo Frames

in Categories , last updated October 26, 2012

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.
smitty -a
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                      [1024]                                                      +#
  Transmit descriptor queue size                     [512]                                                       +#
  Software transmit queue size                       [8192]                                                      +#
  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

(Fig.01: A typical smitty screen to set MTU)

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

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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