How did 1500 bytes become the MTU of the Internet?





[Benjojo] became interested in where the 1,500-byte magic number came from, and shared some background on how and why it appears to have originated. In a nutshell, the maximum transmission unit (MTU) limits the maximum amount of data that can be sent in a single network layer transaction, but 1500 is a bit of an odd number in binary. For the average internet user, this under the hood stuff doesn’t really affect one’s ability to transmit data, but it does have an impact from a network management standpoint. Where does this number come from and why does it matter?

[Benjojo] looks at a year’s worth of data from a major internet traffic interchange and shows using several graphs that being stuck with an MTU cap of 1,500 bytes has a real impact on modern network efficiency and bandwidth usage, because the bandwidth spent on packet headers ramps up quickly when about 20% of all packets exceed the 1,500 byte limit. Of course there are solutions to improve this situation, but elegant and effective solutions to the legacy problems of the Internet usually require immediate support and cooperation from everyone at once, meaning they end up heading in the general direction of nowhere.

So where did 1500 bytes come from? It appears to be a legacy value originally derived from a combination of hardware limits and the need to choose a value that would work well on shared network segments, without causing too much transmission latency when busy and not too much. involves a lot of header overhead. But the picture is not quite complete, and [Benjojo] asks that if you have additional knowledge or insight about the 1500-byte decision, please share it because manuals, mailing list archives, and other context from that era are either disappearing quickly or have already disappeared altogether.

Knowledge disappearing from the archive and memory is definitely something that happens, but every once in a while things get stored instead of disappearing into the shadows. so we have IGNITION! An Informal History of Liquid Rocket Propellants, which contains knowledge and history that would otherwise simply have disappeared.




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