Topic: Setting mtu for eth0

[Paul van Dun]

Hello everybody,

My server is equiped with a gigabit lancard but it's mtu is set to 1500, when I enter the following command on the command line the mtu will be set to 3000

Line: ifconfig eth0 mtu 3000

Is it possible to load this at boottime in the file modules.conf and if so, how should it be entered.
The line of modules.conf looks like this

alias eth0 dpm     <--- this nic can be set to 3000
alias eth1 rtl8139

It's not a big issue but I want to test if this wil make it faster or not,

Looking forward to your replies,

Ragards

Paul van Dun
The Netherlands

[Nathan Fowler]

Just slap ifconfig eth0 mtu 3000 in /etc/rc.d/rc.local so it loads on boot.

[Paul van Dun]

Thankx Nathan,


I will try it tonight when I'm home from work.


Regards,


Paul

[Charlie Brady]

Paul van Dun wrote:

> My server is equiped with a gigabit lancard but it's mtu is
> set to 1500, when I enter the following command on the
> command line the mtu will be set to 3000
>
> Line: ifconfig eth0 mtu 3000
>
> Is it possible to load this at boottime in the file
> modules.conf

Yes, but not in modules.conf.

Create the directory /etc/e-smith/templates-custom/\
etc/sysconfig/network-scripts/ifcfg-eth0/ and within it create the file "MTU" containing "MTU=3000". Then do:

/sbin/e-smith/signal-event post-upgrade
/sbin/e-smith/signal-event reboot

Charlie

[Dub Dublin]

FWIW, most cards capable of using "jumbo frames" as they're commonly called can go all the way up to 9000 byte MTUs.

Jumbo frames are common in the Unix world, especially when running NFS, since an entire 8K NFS block can be sent in a single packet this way.  Of course, whatever's on the other end has to support jumbo frames, too, as well as any routers and/or switches in between.

This is the difference between cheap gigabit routers/switches and expensive ones:  It seems you can't get one to handle jumbo frames without paying a very substantial premium for name brand gear.

(FWIW, if you're after performance with GigE, avoid Cisco like the plague - they have very shallow buffers.  Extereme Networks' stuff keeps up with whatever you can throw at it.  I did extensive GigE performance work on this subject last year...)

[Paul van Dun]

Thanks guys,

I'd like to thank you for your replies, only the solution from Charly didn't work, but Nathan's did.
The funny part is that with Charlies solution the line was added to the file ifcfg-eth0 but it didn't alter the setting for the MTU.
Does someone know a list of out of the box compatible gigabit NIC's for 5.12 and UP or should I wait until 5.6 which might be using the full RH7.3 kernel to support more hardware ?


Regards,


Paul van Dun

[NickR]

Intel is the only one, I think.  I have compiled a module for the NetGear GA622 which works on sme 5.1.2.  You are welcome to it if you want, just mail me.