I recently needed a way to test if packets were reaching a linux device
I'm testing. The device didn't have tcpdump installed, so I didn't have
a real sniffer. Fortunately all I really needed was confirmation that
packets were arriving. iptables to the rescue! Assuming there are no
existing rules to interfere (i.e. use iptables -F
to clean out any
existing firewall), you can use this to log UDP packets arriving at port
1234:
iptables -A INPUT -p udp --dport 1234 -j LOG
Then tail your syslog and you'll see a message when traffic arrives on UDP 1234.