MTU size: increasing network performance

  • Thread starter Thread starter Paul
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Paul

Hi All,

How do I get the MTU size on my network to very large numbers (9K)? I want
to increase the performance of my network. Does the entire network need to
speak the same MTU szie?

Thanks
 
I set the MTU on the server adapter and on my workstation adapter to 9000
and rebooted. I then tested to see if they could exchange packets with 9000
bytes but the following is what I got.


C:\>ping -f -l 9000 10.0.0.1

Pinging dev1.dev.com [10.0.0.1] with 9000 bytes of data:

Packet needs to be fragmented but DF set.

Ping statistics for 10.0.0.1:
Packets: Sent = 1, Received = 0, Lost = 1 (100% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms


What am I missing?
 
Welcome to the wonderful world of trial and error TCP/IP performance tuning.
Some things to try:

1. Set MTU to 8960

2. Create a DWORD registry entry called EnablePMTUDiscovery and set its
value to 0 in HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

3. Download Dr TCP - this is a GUI which allows you to quickly and easily
change TCP/IP registry settings. You can get it here:

http://www.dslreports.com/drtcp

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP

Paul said:
I set the MTU on the server adapter and on my workstation adapter to 9000
and rebooted. I then tested to see if they could exchange packets with 9000
bytes but the following is what I got.


C:\>ping -f -l 9000 10.0.0.1

Pinging dev1.dev.com [10.0.0.1] with 9000 bytes of data:

Packet needs to be fragmented but DF set.

Ping statistics for 10.0.0.1:
Packets: Sent = 1, Received = 0, Lost = 1 (100% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms


What am I missing?


Doug Sherman said:
You can set MTU size on a per adapter basis. Use regedit and navigate to:
HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces

Create a new DWORD entry called "MTU". Values are in bytes, eg. 1.5 KB
="1500".

For a general guide to Windows 2000 performance tuning, see:
Click to expand...
http://www.microsoft.com/technet/prodtechnol/windows2000serv/maintain/optimi
ze/perftune.mspx#XSLTsection127121120120

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP
Click to expand...
need
to
Click to expand...
Click to expand...
 
Hello,

The ping with MTU set to 9000 failed because a routing device needs to
fragment the packet. Scale back on the MTU size until you get a success.
Example: Ping -f -l 8000 10.0.0.1, ping -f -l 7000 10.0.0.1 etc.... Until
you get a reply. This will get you the MTU that the routing device will
accept.

Shane Brasher
MCSE (2003,2000,NT),MCSA Security, Network+, A+
Microsoft Technical Support

This posting is provided "AS IS" with no warranties, and confers no rights.
 
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