Question & Answer
Question
I have an AIX vNIC setup with MTU 1500 as below.
AIX VIO Client - lpar1
en0: 10.0.0.24
vNIC Client Adapter: ent0
VIO Server - vios1
vNIC Server Adapter: vnicserver0
Backing Device: ent8 - PCIe3 4-Port 10GbE SR Adapter VF(df1028e21410e304)
Backing Device Location: U78C9.001.WZS0459-P1-C4-T1-S6
Backing Device: ent8 - PCIe3 4-Port 10GbE SR Adapter VF(df1028e21410e304)
Backing Device Location: U78C9.001.WZS0459-P1-C4-T1-S6
What are the steps to enable jumbo frame to use MTU 9000?
Answer
The figure below illustrates the vNIC configuration on AIX VIO Client.
AIX and VIOS use MTU 1500 by default. When jumbo frame is enabled, MTU is changed to 9000. There are two steps as below to enable jumbo frame.
► Step 1: On HMC, change the MTU of the Physical Port to 9000
• From "Hardware Virtualized I/O" screen, select the physical port U78C9.001.WZS0459-P1-C4-T1
• Select "Modify Physical Port" by clicking "Action" and change "MTU Size" to 9000
► Step 2: On lpar1, change jumbo_frames from no to yes
This change impacts connectivity by using en0 so plan appropriately. Make this change using console connection.
ifconfig en0 down; ifconfig en0 detach
chdev -l ent0 -a jumbo_frames=yes
chdev -l en0 -a state=up
mkdev -l inet0
Run "netstat -in | grep en0" to verify that MTU is set to 9000. If it is not, then run following command to change MTU to 9000.
chdev -l en0 -a mtu=9000
Notes:
(1) It is required to enable jumbo frame on all network devices (e.g. switches, routers, load balancers, firewalls etc.) in between along with on the source and destination hosts to use jumbo frame.
(2) No changes are needed on vnicserver0 and backing device ent8 on vios1.
Author: Darshan Patel
Platform: AIX on Power
Feedback: aix_feedback@wwpdl.vnet.ibm.com
Platform: AIX on Power
Feedback: aix_feedback@wwpdl.vnet.ibm.com
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Modified date:
22 September 2025
UID
ibm16612947