Anyone know of an IP sniffer?

[Rodney Black]

We have a couple of Java applications exchanging data via RTP (we think
we have RTP enabled) on top of UDP between two G4's with YDL 2.1 and
everything tests fine.  We then substituted an embedded system (which
functions fine in a commercial product) for one of the G4s. The embedded
system can receive from the G4 and transmit (as verified by examining
the output from a network sniffer), but the Java application receives no
indication that the G4 received the reply (we did veirfy IP addresses
and port numbers).  So, my first question is "Does anyone know if the
YDL 2.1 IP protocol stack supports RTP?"  If the answer is it does not,
then we go back to the drawing board.  If it does, then the followup
questions are "How does one set up an RTP socket through Java?" and
"Does anyone know of a Linux sniffer (particularly on the YDL disks)
that we can use to determine if the G4 is receiving the response and
where it is going?"

Thanks.

--
Rodney Black