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How to change MTU size on Windows Xp/Vista/7/2008

May 13th, 2010

Sometimes when you are use VPN or Dial-UP based remote connection you need to change the size of MTU.

What is the MTU?

In computer networking, the maximum transmission unit (MTU) of a layer of a communications protocol is the size (in bytes) of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). Standards (Ethernet, for example) can fix the size of an MTU; or systems (such as point-to-point serial links) may decide MTU at connect time. A higher MTU brings greater efficiency because:

  • each packet carries more user-data
  • protocol overheads, such as headers or underlying per-packet delays, remain fixed,
  • higher efficiency means a slight improvement in bulk protocol throughput

However, large packets can occupy a slow link for some time, causing greater delays to following packets and increasing lag and minimum latency. For example, a 1500-byte packet, the largest allowed by Ethernet at the network layer (and hence over most of the Internet), ties up a 14.4k modem for about one second. (WIKIPEDIA)

How can I Change ?

1. Solution

Via CMD line (i changed the default value to 1300):

netsh interface ipv4 set subinterface "Local Area Connection" mtu=1300 store=persistent

Of course REBOOT needed.

1.1 If do you what to verify this setting:

netsh int ip show int

Response is:

Idx Met MTU State Name
--- --- ----- ----------- -------------------
1 50 4294967295 connected Loopback Pseudo-Interface 1
10 10 1500 connected Local Area Connection
19 20 1500 connected VirtualBox Host-Only Network

2. Solution

1. run REGEDIT.exe
2. Go to : HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\Interfaces
3. Select the Interface what do you want to config  example interface value: {111112-3344545-666666-777777}
4. Rich Click on Right Side and create a new RegWord type with:

    name: MTU
    value: 1300
    base: Decimal
    or  value: 514
    base: Hexadecimal

5. Restart the System

3. Solution

Download this application:

http://www.dslreports.com/drtcp

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