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

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.

Answer 3

I've written a multicast testing application back in the day.
You can check it out here: https://github.com/eranbetzalel/SimpleMulticastAnalyzer

Answer 4

This is the first hit when I searched for capturing multicast packets using netcat, and I found out that tcpdump does a job better. Just making a note for any one else hitting this post.
To install:
sudo apt install tcpdump
To run:
tcpdump -c 8 -n -i eth0 portrange 1234-1239
looks like there may be a Windows port too, but I didn't try it: https://www.winpcap.org/windump/