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How to view MTU size in Windows Vista

It has always frustrated me that ipconfig /all in windows does not show me the currently active MTU size on a given adaptor (like it does in most OS’s).  Up until now I was not aware of any way to get this information (beyond maybe looking up the setting in the registry).

I just discovered the following command in Windows Vista (you have to be running command prompt as admin):

C:\Windows\system32>netsh interface ipv4 show subinterface

   MTU  MediaSenseState   Bytes In  Bytes Out  Interface
——  —————  ———  ———  ————-
4294967295                1          0      41533  Loopback Pseudo-Interface 1
  1300                1    7853050    1403618  Wireless Network Connection
  1300                5          0      23616  Local Area Connection
  1500                5          0          0  Bluetooth Network Connection
C:\Windows\system32>

Note that my MTU sizes on my LAN and Wireless cards are 1300, because the Cisco VPN client is installed, and I believe it sets them low to avoid PMTU issues.

This command does not work in Windows XP or Windows Server 2003 as it complains that RRAS is not running (I suspect it would work if RRAS *was* running).

-Eric

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