RE: howto increase MTU size?

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx, horms@xxxxxxxxxxxx, ja@xxxxxx, ratz@xxxxxx, jmack@xxxxxxxx
Subject: RE: howto increase MTU size?
From: Michael_E_Brown@xxxxxxxx
Date: Thu, 25 Apr 2002 15:25:50 -0500
You must have a switch that supports jumbo frames, or you won't get very
far. The switch will dump oversize frames if it isn't configured for jumbo

> -----Original Message-----
> From: Joseph Mack [mailto:mack.joseph@xxxxxxx]
> Sent: Thursday, April 25, 2002 2:12 PM
> To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx; Horms; Julian Anastasov; Roberto
> Nibali; jmack@xxxxxxxx
> Subject: howto increase MTU size?
> according to
> the MTU of 1500 was chosen for 10Mbps ethernet and was kept
> for 100Mbps and 1Gbps ethernet for backwards compatibility
> on mixed networks. However MTU=1500 is too small
> for 100Mbps and 1Gbps ethernet. In Gbps ethernet jumbo frames
> (ie bigger MTU) is used to increase throughput.
> On my LVS performance page I found that decreasing the MTU
> decreased max throughput on 100Mbps ethernet. Since the decrease
> was approx linear with MTU, I wondered if the linearity would
> still be linear beyond 1500, and if increasing the MTU
> on 100Mbps would increase max throughput (ignoring
> the problem of fragmenting packets once they got off the LAN).
> I couldn't increase the MTU above 1500 with ifconfig or ip link.
> I found that the MTU seemed to be defined in 
> linux/include/if_ether.h 
> as 
> and increased these by 1500, recompiled the kernel and net-tools
> and rebooted. I still can't install a device with MTU>1500
> Any suggestions?
> Thanks
> Joe
> -- 
> Joseph Mack PhD, Senior Systems Engineer, Lockheed Martin
> contractor to the National Environmental Supercomputer Center, 
> mailto:mack.joseph@xxxxxxx ph# 919-541-0007, RTP, NC, USA
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