Re: Gigabit and MTU > 1500

fr den 03.03.2006 klokka 07:40 (-0500) skreiv Nicolas Ross:
> Hi !
> 
> Currently, I have a linux router with a gigabit trunk to a 10/100 swith. 
> This trunk passes vlan tag to different vlan interface in the linux box.
> 
> We will be adding a 24 port gigabit swith soon. We then will have a gigabit 
> segment. On that segment, we plan on unsing jumbo frames (9000 or the like). 
> So, I'll have to crank up the eth undelaying card of the linux router to 
> 9000 to support such packets. New vlan interface will default then to a mtu 
> of 9000 (I think so).

In practice I don't think this will give you a lot performance-wise. The
most of the world is at 1500 bytes so the MTU in use at most of the time
would probably be 1500. 

This could work in a scenario where you are doing large transaction
where window scaling max out to 9000 bytes.  

> But we have some other vlan that needs to stay at 1500. If I specify in the 
> ifconfig command the MTU, will this work as I expected ?

yes

> Also, is there a way to specify de MTU in the ifcfg-vlanxxx file in 
> sysconfig/network-scripts ?

at least in Fedora, yes :)