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