So you think you understand IP fragmentation?

Posted Feb 9, 2024 17:58 UTC (Fri) by farnz (subscriber, #17727)
In reply to: So you think you understand IP fragmentation? by paulj
Parent article: So you think you understand IP fragmentation?

By 1990, it was already the case IME that communication was not possible if there were smaller MTUs in the path, unless you were lucky enough to have a path where everything was run by sensible netadmins (usually true of academia), or you were on dial-up (where you had the bottleneck MTU).

And one of the many issues back then was routers with multi-MTU paths that were configured explicitly to not fragment packets because it could overload the CPU; packets were either pre-fragmented, or were dropped. Add in people configuring routers to drop fragments "because security" (which got worse after the ping of death vulnerability was discovered, since that depended on buggy fragment handling), and fragmentation became useless.

The IETF, by limiting fragmentation to the endpoints, were reacting to the state of play in 1990, where many routers already didn't fragment, but dropped packets that were too big.