HOWTO determin the Maximum Transfer Unit

[TheMillionDollarMan]

I would like to detect the MTU of my network.

At the moment I just monitor the amount of TCP packets sent/recevied on a workstation. Its only at 10mbps.

from tracert I can see only one switch between my 100Mbps NIC workstation and the 1000MBPS server so can I assume that this switch/router is the bottle neck?

Thanks

 

[vbrocks]

If there is another nic on the same segment using 10mbs that will do the same thing...

 

[ACraib]

try using

ping <servername> -f -l 1500

The -f switch forces the packet not to fragment. then adjust the -l value down until you get a correct printg respoonse.

 

[itsp1965]

It also depends on what OS you're using. I am assuming you are working in a Windows environment so you can find MTU size in the registry. The default would be 1514/1518 for Ethernet although I do recall that some of the client OSses were running at 576. There is a good document on the MS website on tuning the TCP/IP stack in order to get optimal results

 

[shorty545]

The switch/router should auto-negotiate its settings with each node on the network. If your PC has a 10/100 nic card it will choose the best connection, usually a 100/full duplex mode. The MTU should not affect the MB/s rate. The MTU will only set the maximum length for each packet. By default the MTU is somewhere between 1500 and 1550, I believe. If you lower this, your PC will still send at a rate of 100MBs, but the packet length will be shorter, and the CPU usage will increase.

You may want to check the settings of your switch to see if it is indeed a 10/100 switch and make sure it is set to auto-negotiate. You may also want to try and hard code the switch to 100MB/s for the single port the PC you are monitoring is on, and see if that increases the throughput.

Jeremy

 

[vbrocks]

Some nics have two different outputs (10Mbs BNC) AND (100 Mbs RJ-45), make sure you are using the right one....