MTU

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<interface-name>

Description

Reduces the size of the maximum transmission unit (MTU) TCP/IP uses for the network interface. The value of this entry overrides the MTU detected dynamically by the network adapter.

The MTU is the size of the largest packet that can be transmitted over the underlying network, including the size of the transport header. The MTU is configured separately for each interface.

To prevent fragmentation, the MTU should be large enough to hold any IP datagram in a single frame. IP datagrams larger than the MTU are divided into fragments whose size is a multiple of eight octets. The fragments travel separately to the destination computer, where they are reassembled before the datagram is processed.

MTU detection is determined for all interfaces by the value of EnablePMTUDiscovery. By default, the network adapter for each interface detects the largest MTU that can be transmitted by the interface and uses that for its transmissions. However, if MTU detection is disabled (that is, the value of EnablePMTUDiscovery is 0), the system uses a fixed MTU of 576 bytes. If you change the default value of MTU, you override either setting as it pertains to the interface represented by this subkey.

Note

If you enter a value greater than the dynamically-determined MTU, the system uses the value of the dynamically-determined MTU instead. You can use this entry to reduce, but not to increase, the size of the MTU.

Windows 2000 does not add this entry to the registry. You can add it by editing the registry or by using a program that edits the registry.

Tip

For more information, search the Microsoft Knowledge Base for articles that include the term MTU or PMTU.

Caution

In general, replacing a dynamically determined value with a fixed value degrades the performance of the operating system. Do not change the value of this entry unless the detected MTU is not compatible with the network media.

Related Entries

EnablePMTUDiscovery