[ILUG] tcpdump .. and friends

[Declan Grady]

Hi,
I need some help finding a windows (98/me/xp) box which is sending port 30001 
stuff.
My ipchians firewall is rejecting udp from  132.25.4.169:30001 to 
255.255.255.255:30001

tcpdump shows these packets on my eth0 (lan int) every 20 seconds.
but only gives the 132.5.24.169 address...

My local lan is all 192.168.0.xxx
How can I find which box is sending the packet ?

Thanks,
Declan