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How to Change AIX MTU Size

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AIX MTU

In some situations, Maximum Transmission Unit (MTU) size should not be optimized as high as 9000. Instead, 1500 could be the right choice for your AIX system.

Let's see current status of MTU on en0 and en1.

[root@primary01 /]# lsattr -El en0 | grep mtu
mtu           9000          Maximum IP Packet Size for This Device        True
mtu_bypass    on            Enable/Disable largesend for virtual Ethernet True
remmtu        576           Maximum IP Packet Size for REMOTE Networks    True
[root@primary01 /]# lsattr -El en1 | grep mtu
mtu           9000          Maximum IP Packet Size for This Device        True
mtu_bypass    on            Enable/Disable largesend for virtual Ethernet True
remmtu        576           Maximum IP Packet Size for REMOTE Networks    True

We changed both values back to 1500.

[root@primary01 /]# chdev -l en0 -a mtu=1500
en0 changed
[root@primary01 /]# chdev -l en1 -a mtu=1500
en1 changed

Then we check the results.

[root@primary01 /]# lsattr -El en0 | grep mtu
mtu           1500          Maximum IP Packet Size for This Device        True
mtu_bypass    on            Enable/Disable largesend for virtual Ethernet True
remmtu        576           Maximum IP Packet Size for REMOTE Networks    True
[root@primary01 /]# lsattr -El en1 | grep mtu
mtu           1500          Maximum IP Packet Size for This Device        True
mtu_bypass    on            Enable/Disable largesend for virtual Ethernet True
remmtu        576           Maximum IP Packet Size for REMOTE Networks    True

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