[En-Nut-Discussion] UDP problem to recv datagram bigger than 1500

Ole Reinhardt ole.reinhardt at embedded-it.de
Wed Sep 3 00:09:34 CEST 2014


Am 02.09.2014 22:12, schrieb SnailHero:
> I am writing an application for NUT/OS 5.2 and I am facing some problem:
> When sending datagram smaller than 1500 everything is ok.
> But when I try to send something bigger
> The function:
> got = NutUdpReceiveFrom(sock, &clientIP, &clientPort, buf, 2600,
> always timeout and return 0

That is because Nut/OS does not support IP fragmentation. The MTU of the
network interface is 1500 bytes. So packages larger than 1500 Bytes
would get fragmented. And unfortunately this is not supported...

Especially for low-ressource devices like the AVRs, handling of
fragmentation requests too much resources. So from historical reasons
and downward compatibility Nut/OS does not support fragmentation.

Perhaps we should implement in the future?



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