Any small program to receive multicast packets on specified UDP port?

Question

I'd like to debug some multicast issues, and I hope to have some small programs/utilities to display incoming multicast packets.

From the sending machine(A), I use Richard Stevens's sock program(provided with his TCP/IP Illustrated book Vol1) to send multicast packets(source port=dest port=7000), like this:

sock -u -b 7000 224.0.0.7 7000

On the receiving machine(B), I can capture the very sent packet with Wireshark, however, the same sock command running on B does not report receiving anything.

Then, what program should I use on B to see incoming multicast packets, aside from Wireshark which is overkill.

Linux and Windows programs are both welcome.

Answer 1

Here's a python script that will print the incoming data;

# Multicast client
# Adapted from: http://chaos.weblogs.us/archives/164

import socket

ANY = "0.0.0.0" 
MCAST_ADDR = "224.0.0.7"
MCAST_PORT = 7000

# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)

# Allow multiple sockets to use the same PORT number
sock.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)

# Bind to the port that we know will receive multicast data
sock.bind((ANY,MCAST_PORT))

# Tell the kernel that we want to add ourselves to a multicast group
# The address for the multicast group is the third param
status = sock.setsockopt(socket.IPPROTO_IP,
socket.IP_ADD_MEMBERSHIP,
socket.inet_aton(MCAST_ADDR) + socket.inet_aton(ANY))

# setblocking(0) is equiv to settimeout(0.0) which means we poll the socket.
# But this will raise an error if recv() or send() can't immediately find or send data. 
sock.setblocking(0)

while 1:
    try:
        data, addr = sock.recvfrom(1024)
    except socket.error as e:
        pass
    else:
        print "From: ", addr
        print "Data: ", data

Answer 2

You can use netcat (nc) to do that:

netcat -vv -l -p 1234 -u

This means netcat is verbosely listening on port 1234 of the localhost in UDP mode.