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Maximum Transmission Unit (MTU)


The maximum transmission unit (MTU) of a network interface is the size of the largest block of data that can be transmitted as a single unit. Anything larger than the MTU must be broken into smaller units prior to transmission. Interfaces with different MTUs should not normally be mixed on a given Internet Protocol subnet, however it is possible (and not uncommon) for subnets with different MTUs to be connected to each other by means of a router.

MTUs can be measured either at the network layer or at the link layer. For example, the standard Ethernet MTU is 1500 bytes at the network layer but 1518 bytes at the link layer. The values used in this site are network-layer MTUs unless stated otherwise, but be aware that equipment manufacturers often specify link-layer MTUs instead.

The MTU of a network interface may be configurable. Faster networks tend to benefit from having a higher MTU, but it is also necessary to take account of hardware limitations and the need to avoid mixing MTUs within a subnet.


Further reading