Unfortunately, I was wrong - the MTU is still a fixed setting, in Vista. The legendary tool, DrTCP, which is used by everybody to change the MTU in Windows 2000 and XP, doesn't work under Windows Vista. Fortunately, Microsoft now allows us to adjust the MTU using the "netsh" command.

Set-NetIPInterface Specifies the network layer Maximum Transmission Unit (MTU) value, in bytes, for an IP interface. For IPv4 the minimum value is 576 bytes. For IPv6 the minimum is value is 1280 bytes. For both IPv4 and IPv6, the maximum value is 2^32-1 (4294967295). You cannot set values outside these ranges. What is MTU Size and What Should I Set it to? - Home What Exactly Is MTU? MTU stands for Maximum Transmission Unit. This is just one of many settings that you may have to adjust to fully optimize your router. The MTU size is a setting that determines the largest packet size that can be transmitted through your system. These packets are measured in octets, or eight-bit bytes. PChucks Network: Setting The MTU In Windows Vista Long ago, when I first heard of the dynamic tuning in the Windows Vista TCP/IP stack, I envisioned the manual setting of the static MTU to be a thing of the past. Unfortunately, I was wrong - the MTU is still a fixed setting, in Vista. The legendary tool, DrTCP, which is used by everybody to change the MTU in Windows 2000 and XP, doesn't work under Windows Vista.

Jul 26, 2012

No question MTU can cause problems. Often when you can see files and browse successfully, but fail when opening or copying files, it is an MTU issue. PPTP VPN's require an MTU of 1430 or less. I assume if you are using the WatchGuard you are using IPSec, for which I have never seen a specific MTU requirement.

Resize MTU in Windows – Zyxel Support Campus EMEA

Personally I have never had to manually manipulate the MTU value on any of my PCs ever. MS-MVP Windows Desktop Experience, "When all else fails, read the instructions" MS-MVP Windows Expert - Consumer "When all else fails read the instructions"