> Does linux 's kernel implement Path MTU discovery in UDP packets (IPv4)? I
Yes.
> runned tcpdump and i saw that TCP packets usind Don't Fragment bit while
> UDP packets don't use. Why?
PMTU discovery is useless for UDP at the moment, so that it is turned
off by default.
> I saw that Solaris use Path MTU in UDP packets too.
The problem is that UDP does not retransmit. If pmtu discovery
on UDP solved some (even minor) problem, we would enable it.
It does not as of 2.2 and 2.3, so that it is not worth to loose
packets without any clear purpose. I have no idea why sun folks
did it.
BTW one application for pmtu discovery for udp is found and
it is enabled by default in patch
ftp://ftp.inr.ac.ru/ip-routing/softnet-*.dif.gz
Alexey
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