I wrote: > 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. Rick Stevens answered: > 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. Thanks. But that doesn't make any obvious difference. Still no output. If examining the packets were my only concern, tcpdump would do just fine. But I actually have a program which would like to receive those packets and doesn't. Using NC is part of the investigation to discover why not. But NC doesn't seem to get the packets, either. -- Dave Close -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
