On 06/26/2014 09:53 AM, CLOSE Dave issued this missive:
I have a Fedora 20 machine which is receiving UDP broadcast packets at
regular intervals on a strange high port. No program is presently
listening for these packets. If I run, "tcpdump -i eth0 port 29531", I
see each of the packets arriving just as I expect. Note, the packets are
not empty and contain mostly ASCII characters.
But if I then run, "nc -lu 29531", I don't see anything! Why not? What
obvious thing am I missing?
This same operation works better (but still not as I expect) on Fedora
14. NC shows one packet arriving but then doesn't show any more.
Running NC under strace on both machines, I see F14 NC seems to use
poll(2). It outputs one packet then hangs on poll. F20 NC seems to use
select(2). It hangs on the first call.
SELinux and the firewall are disabled on both machines.
You may need to use "nc -lu --recv-only 29531" so the system doesn't
try to reply to the packet. Perhaps it's better to use wireshark or
tcpdump to copy the data to a file and examine it.
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