MTU (Maximum Transmission Unit)

What is MTU

MTU (Maximum Transmission Unit) is a computer networking term that describes the largest data package size that can be sent through either a packet or frame-based network. It is one of the standards that the Transmission Control Protocol that the Internet uses to navigate data transfer uses to set up the maximum size of each data package during a transmission. MTU uses eight-bit bytes (octets) to determine the parameters of each package. You will often come across the term MTU (Maximum Transmission Unit) together with the Ethernet protocol. The largest size of the data package under Ethernet standards is 1500 bytes.

MTU and Fragmentation

What if you need to transfer packages that exceed these 1500 bytes? MTU fixes that issue using a process called Fragmentation. IPv4 allows dividing the basic data units in a packet-switched network into smaller pieces that fit the necessary size. In that way, the units can pass through the MTU process. The fragmentation happens on the IP level where the packages are marked as fragmented and then transmitted over the network. In that way, when the receiving network gets the packages, it knows that they need to be reassembled and in what order to do that. In some cases, applications don’t allow data fragmentation. In these, instead of MTU, networks use TCP MSS (Maximum Segment Size) to circumvent the issue.