Maximum Transmission Unit (MTU)
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4/8/2010
Each media type has a maximum frame size that cannot be exceeded. The link layer is responsible for discovering this MTU and reporting it to the protocols above the link layer. NDIS drivers may be queried for the local MTU by the protocol stack. Knowledge of the MTU for an interface is used by upper layer protocols such as TCP, which optimizes packet sizes for each media automatically. For more information about TCP Path Maximum Transmission Unit (PMTU) discovery, see Path Maximum Transmission Unit (PMTU) Discovery.
Note
The minimum MTU for IPv6 is 1280 bytes.
If a NIC driver — such as an ATM driver — uses LAN emulation mode, it may report that it has an MTU that is higher than what is expected for that media type. For example, it may emulate Ethernet but report an MTU of 9180 bytes. Windows Embedded CE accepts and uses the MTU size reported by the adapter even when it exceeds the normal MTU for a given media type.
For information about enabling TCP to discover the MTU or largest packet size, see TCP/IPv4 Configurable Registry Settings.