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. ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@xxxxxxxxxxxxxx - - AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 - - - - NEWS FLASH! Intelligence of mankind decreasing! Details at... - - uh, when, uh, the little hand is, uh, on the... Aw, NUTS! - ---------------------------------------------------------------------- -- 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
