(Some) received packets are not reaching a listening application (UDP?)
Hello everybody,
I have an issue with an application not receiving all traffic that it
should be getting. The current system is a non-Debian GNU/Linux, but
since I had a similar issue using Debian and I am not following any
other Linux-related list, I hope not to be off topic. I have taken the
liberty to CC debian-kernel because I feel that the kernel is getting
the packets but not forwarding them.
The first experience--using the Debian system--was some months ago, so
accuracy is not guaranteed. At that time I had decided to try
configuring network autodetection (on a laptop using a 10/100 Broadcom
Ethernet chipset, and a 2.6.x packaged kernel) using one of Debian's
packages, laptop-net, I think. Under ordinary circumstances I did not
manage to make it work. However, when capturing traffic with Ethereal,
I found that the IP was correctly configured from the previous
arbitrary state. The situation was weired, I wasn't really moving
around much and time was scarce, so I let the issue drop.
Now I have seen a similar situation with syslog running under a RedHat
system with a 2.6.9 kernel. This time, capturing traffic on the wire
shows no packet loss, and a tcpdump capture on the interface shows all
messages arriving, but syslog does not log all of them. However, when
running "nc -l -u -p 514 > /dev/null", without stopping the syslog
daemon, all messages are written down. As a matter of fact, it seems
that "nc -l -u -p 514 > /dev/null &" is just as good, but since the
process is stopped automatically not even I quite believe my eyes.
I hope that somebody can offer some insight as to what might be
happening or how to look deeper into the problem. I might not be able
to readily work on the affected system, but it would anyway be good to
get some tips as to how to further look into the problem. Hints about
the reason and, why not, how to mend the situation would also work
wonders. Thanks.
--
Gonzalo HIGUERA DÍAZ <gonhidi@gmail.com>
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