The latest versions of AIX now allow largesend on virtual adapters to remain persistent across reboots. I cant find any information for this attribute in the AIX 7.1 Information center yet.

The new attrribute is called mtu_bypass and can be changed with the chdev command. e.g

; AIX 7.1 TL1 SP2.

# oslevel -s

7100-01-02-1150

; LARGESEND is off.

# ifconfig en1

en1: flags=1e080863,480<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD(ACTIVE),CHAIN>

inet 10.153.20.46 netmask 0xffff0000 broadcast 10.153.255.255

tcp_sendspace 262144 tcp_recvspace 262144 rfc1323 1

; mtu_bypass is disabled.

# lsattr -El en1 -a mtu_bypass

mtu_bypass off Enable/Disable largesend for virtual Ethernet True

; mtu_bypass is now enabled.

# chdev -l en1 -a mtu_bypass=on

en1 changed

# lsattr -El en1 -a mtu_bypass

mtu_bypass on Enable/Disable largesend for virtual Ethernet True

; LARGESEND is on.

# ifconfig en1

en1: flags=1e080862,4c0<BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD(ACTIVE),LARGESEND,CHAIN>

inet 10.153.20.46 netmask 0xffff0000 broadcast 10.153.255.255

tcp_sendspace 262144 tcp_recvspace 262144 rfc1323 1