Maximal Transfer Unit

Maximal Transfer Unit is the largest possibl layer 2 frame size on a network.

Ethernet uses a 1500-byte in the 10Mbps and 100Mbps forms, and commonly uses 9000-byte MTUs in 1000Mbit (Gigabit) ethernet. Ethernet MTus can be as high as 16384 bytes.

PPPoE connections and other tunnels will often use a MTU of 1492, to accout for the tunnel overhead.

Other (less common) MTU sizes:

• 16 Mbit/Sec Token Ring: 17914
• 4 Mbits/Sec Token Ring: 4464
• SONET: 4460
• FDDI: 4352
• X.25: 576

ATM uses a cell size of 53 bytes, but the LANE layer on top of it emulates a larger MTU.