Re: mtu

["Igor Gueths" <igueths@yahoo.com>]

Hi Kerry. I actually have an lne100TX, and I think it does pretty good for speed. What other options could I tweak for speed improvements could I manipulate? 
----- Original Message ----- 
From: Kerry Hoath <kerry@gotss.net>
To: <speakup@braille.uwo.ca>
Sent: Tuesday, March 26, 2002 3:23 PM
Subject: Re: mtu


> The ethernet frame size is 1524 bytes. You can't
> raise the mtu higher than that you just end up with a pile of back to back
> full-sized ethernet frames and loose performance due to the
> fragmentation.
> What transferrs are you trying to speed up and what sort of card is this? There may
> be other options you can tweak that don't involve fooling with the 
> framesize on ethernet.
> Increasing mtu can also cause problems with cards that are not capable of
> receiving giant frames. You're also violating
> the ethernet standards if you exceed the maximum framesize.
> I doubt you will gain any performance by reducing wire overhead, your
> need for speed can be solved in other ways. How fast is this machine and is the
> card isa/pci?
> If it isn't a pci busmaster and is an rtl8029, it's a cheap
> card and is a connectivity solution. Snap it in half and go buy a real card
> if speed and system performance is important to you or tolerate
> the slower speeds to save money.
> 3com 905 cards cost a lot of money for a good reason, they are fast
> efficient and easy on cpu.
> The rtl8029 and rtl8139 are mass market pci ethernet chips that aren't known
> for speed. Linux usually drives them as best it can but
> there are all sorts of hardware limitations to work around and
> bugs that bite.
> 
> Regards, Kerry.
> On Tue, Mar 26, 2002 at 02:28:26PM -0500, Igor Gueths wrote:
> > Hi Kerry. Wouldn't increasing the mtu value decrease over head? Because I am trying to raise the value to 10000 or something, not lower it. 
> > ----- Original Message ----- 
> > From: Kerry Hoath <kerry@gotss.net>
> > To: <speakup@braille.uwo.ca>
> > Sent: Tuesday, March 26, 2002 6:46 AM
> > Subject: Re: mtu
> > 
> > 
> > > I can't see why you'd want to do this on an ethernet
> > > interface anyway since ethernet is tuned to handle mtu of 1500 and reducing it
> > > is just going to increase wire overhead and do nothing more.
> > > MTU discovery means that if something else has a lower mtu this will be communicated back
> > > to the kernel and th e networking stack will take care of it.
> > > Well just because I don't know why you want to do this doesn't mean it can't be done.
> > > Once the route to the interface is in place you need to del the route and re-add it
> > > with the mtu value so for example:
> > > route del 192.168.1.0
> > > route add -net 192.168.1.0 dev eth0 mtu 768
> > > and I think the ip tools can do this too
> > > try ip route help 
> > > and
> > > ip nei help
> > > 
> > > Regards, Kerry.
> > > On Mon, Mar 25, 2002 at 08:19:13PM -0500, Igor Gueths wrote:
> > > > Hi. Has anyone successfully changed their mtu value on their network interface? I am unable to do this via /etc/network/interfaces. I put mtu 1000 after the line where it says iface eth0 inet dhcp. I restarted inetd and init, and the value hasn't changed. Does anyone know how to go about doing this? Thanks! 
> > > > 
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