Changing MTU size on client machines

Changing MTU size on client machines

Post by R2xlbm4gVG » Mon, 14 Jan 2008 07:53:01


I have a c# application hitting an web service. .net 2.0

I have been told by a customer of mine that it is necessary that I reduce
the MTU size of all my outbound client web requests to 1470. I've done a bit
of searching on the topic, and it is apparent to me that this can only be set
at the client machine level through a registry modification, not through my
application itself. Is this correct? Is there a way that my c# code, through
digging into the webservice proxy class to get to the Syste.Net.Socket
object, can chance this?

Thanks for any help,

Glenn Thimmes

Changing MTU size on client machines

Post by Spam Catch » Tue, 15 Jan 2008 16:20:06

=?Utf-8?B?R2xlbm4gVGhpbW1lcw==?= <Glenn
XXXX@XXXXX.COM > wrote in

Why? MTU should be handled by the operating system ... or by a
knowledgable user. Your application should not be messing with the MTU.

MTU is controlled via a registry entry.

Correct - most applications do not need to modify the MTU.

Any particular reason you need to modify the MTU?

XXXX@XXXXX.COM (Do not e-mail)


Changing MTU size on client machines

Post by R2xlbm4gVG » Tue, 15 Jan 2008 21:44:03

The reason is that a customer has reported that network traffic is not
performing optimally becuaes MTU size is larger that what is configured by
their routers. To me this seems like their problem, since they are in charge
of configuring thier client machines, but the client claims it is something I
should be controlling in my application itself.


Changing MTU size on client machines

Post by Spam Catch » Wed, 16 Jan 2008 00:17:52

< XXXX@XXXXX.COM > wrote in

Yes, this is a customer issue ... MTU is set by default in the Winsock
and Windows usually has it configured for an optimal value. If the user
has changed their MTU (i.e. with bandwidth tweaking tools), the MTU may
no longer be optimal for the network he/she is on. It is very rare to
need to modify the MTU and is only down by people who want to maximize
download speeds.

One of the best tools for tweaking MTU and other TCP settings is TCP
optimzer, you can download it here:

You can replicate some of the settings from this tool, but it's probably
for you to tell your client to get his/her administrator to understand
MTU and other settings and get them to make their own changes :-)

P.S. Remember the 7 layer OSI model? Your application is resides at the
top Application layer. Network calls by .NET are fed down to the
transport and network layers - which are handled by the OS.

XXXX@XXXXX.COM (Do not e-mail)