Best MTU for single-isdn

[Andreas Klemm]

On Sat, Apr 12, 2003 at 09:07:01PM +0200, Gary Jennejohn wrote:
> Jan Goebel writes:
> > I was just wondering, if the standard ethernet mtu 1500 is best for my isp
> > device, too. Or is it better to lower it a bit?
> > 
> 
> I've always used the default of 1500 with good success.

It depends on your traffic pattern.

Supposed you have often a mix of ftp / http / telnet traffic,
then ftp often tends to monopolize the link.

Cisco router have several queuing options to come around
this problem, i.e. WFQ (waited fair queueing), that has
been made for exactly this purpose, give smaller packets
a chance to come through smaller bandwidth links.

But if you download much this helps you only if your ISP
also uses WFQ, so that receiving ftp streams also don't
monopolize the link.

Using smaller mtu sizes could help you, so that many
different traffic types can make better use of the link.

The downside is, that you loose download performance and
the router has to fragment the packets which is more
CPU intensive as if he would only have to forward the
packets.

If you don't often mix ssh/telnet / ftp/hhtp traffic, then
I would say, save the work and simply use the default of 1500
which is more often desired, to get best download results of
larger files.

	Andreas ///

-- 
Andreas Klemm - Powered by FreeBSD 4.8
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