HOW TO Change the default Maximum Transmission Unit (MTU) Size

The maximum transmission unit (MTU) is the size (in bytes) of the largest protocol data unit that it can pass onwards. MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). The MTU may be fixed by standards (as is the case with Ethernet) or decided at connect time (as is usually the case with point-to-point serial links).

A higher MTU brings greater efficiency because each packet carries more user data while protocol overheads, such as headers or underlying per-packet delays remain fixed, and higher efficiency means a slight improvement in bulk protocol throughput. However, large packets can occupy a slow link for some time, causing greater delays to following packets and increasing lag and minimum latency. For example, a 1500 byte packet, the largest allowed by Ethernet at the network layer (and hence most of the Internet), would tie up a 14.4k modem for about one second.

OK, enough for MTU overview,you can read more on Wikipedia pages.

Now here are the step by step to increase the MTU size, on Solaris of course.

by default, if you type “ifconfig -a” you will get the MTU size is 1500:

bash-3.00# ifconfig -a
lo0: flags=2001000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv4,VIRTUAL> mtu 8232 index 1
inet 127.0.0.1 netmask ff000000
e1000g0: flags=201000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4,CoS> mtu 1500 index 2
inet 10.32.16.1 netmask ffffff00 broadcast 10.32.16.255
ether 8:0:27:73:25:e8
e1000g1: flags=201000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4,CoS> mtu 1500 index 3
inet 10.32.16.2 netmask ffffff00 broadcast 10.32.16.255
ether 8:0:27:6a:34:ae
bash-3.00#

Continue reading