From: Gilbreath, Jeff (jeff.gilbreath@mirant.com)
Date: Mon May 13 2002 - 12:37:19 EDT
Greetings all,
I've come across a head-scratcher that I wanted run by the group.
I've noticed poor performance from our GigE interfaces and while troubleshooting, I decided to turn up
the MTU size, only to discover that I can't.
All testing has been done through both a Cisco Catalyst GigE switch
and through a GigE direct "box to box" link.
Through searching the net I've found many people seeing the same performance
problems. The sunmanagers mailing list has been extremely helpful in providing
tuning info that has resulted in minor performance increases. But the crux of
the issue seems to be the MTU size. While I've found info on the net and sunsolve
on how to change this, when I try to change this on our servers (multi-homed E420R's,
02-20 release) I get the following error:
[root@weblogicdev02] ifconfig ge0 10.11.236.31 netmask 255.255.252.0 mtu 1600
ifconfig: setifmtu: SIOCSLIFMTU: ge0: Invaid argument
I can reset the MTU size to a number lower than the install-default of 1500. But, I can not
reset it to a number that's higher. (Note: When setting to a lower MTU throughput decreases.)
This has been tested through direct connect, the Cisco switch and unplugged. IT JUST WON'T
LET ME SET IT HIGHER. References I've found on the net show that SGI GigE cards are usually
set to a MTU of 9000 instead of Sun's locked 1500. Various Linux resources point to a MTU of
between 7500 and 10000 for optimal GigE performance. So the $64,000 question is: How can this
be reset on a Sun box?
All suggestions are welcome and appreciated. I thank you in advance.
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