Linux built-in or open source program to join multicast group?

Question

I'm using tcpdump to capture multicast packets and had to code up a custom program to join multicast feeds so tcpdump will "see" the packets. Just wondering if netcat or any other applications can perform this function instead?

score 15 · Answer 1 · answered Sep 22 '15 at 08:01

One can use socat to subscribe to groups. This works nicely for both L2 and L3 subscription:

socat STDIO  UDP4-DATAGRAM:239.101.1.68:8889,\
  ip-add-membership=239.0.1.68:10.100.201.1

This will subscribe to group 239.0.1.68 using the interface with address 10.100.201.1. The UDP4-DATAGRAM:239.101.1.68:8889 bit listens for packets on a dummy group and udp port that should not receive any data to prevent socat from also outputting everything to stdout. If, instead, you want to direct the payload to stdout, change that group and port to be actual group and port that you want to subscribe to.

Multiple comma-separated ip-add-membership directives can be specified to subscribe to multiple groups at the same time. When socat exits, it seems to clear out the IGMP subscriptions too.

grawity · Accepted Answer · 2023-07-14T17:55:08.190

12

This answer has been retracted.

edited Jul 14 '23 at 17:55

answered Aug 18 '11 at 16:12

grawity

501,077

score 4 · Answer 3 · answered Feb 05 '23 at 13:36

For future visitors of this thread

Why not use ip addr add ... autojoin? The following works for me to join a multicast ipv4 or ipv6 group:

desktop:~ $ sudo ip addr add ff05:feed:dead:beef:feed:dead:beef:beef dev enp4s0 autojoin
desktop:~ $ # or for ipv4: sudo ip addr add 239.42.42.42/32 dev enp4s0 autojoin
desktop:~ $ # optional check that the address is added:
desktop:~ $ ip addr show
desktop:~ $ # to start listening:
desktop:~ $ netcat -6 -l -k -u -p 9000

On the sender (for ipv6)

pi@blueberry:~ $ echo "Hello multicast" | netcat -w 0 -u ff05:feed:dead:beef:feed:dead:beef:beef 9000

score 3 · Answer 4 · answered Jun 14 '18 at 07:03

3

In addition to socat answer, here is a heavyweight solution - smcroute. This application run as a daemon and can be controlled on the fly:

smcroutectl join eth0 239.1.1.27
smcroutectl leave eth0 239.1.1.27

answered Jun 14 '18 at 07:03

SergA

348

score 1 · Answer 5 · answered Feb 04 '23 at 11:16

1

In FRR's pimd, you can do:

interface vlan2000
 ip address A.B.C.D/24
 ip igmp
 ip igmp join 239.0.110.219
 ip igmp join 239.0.110.220
 ip igmp version 2

answered Feb 04 '23 at 11:16

yasu

11

score 0 · Answer 6 · answered Sep 05 '18 at 12:31

Use the "Receive" part in https://stackoverflow.com/questions/603852/multicast-in-python, omit the definition of the MCAST_PORT and the line "sock.bind ..." and replace the last line (print ...) with pass. That gives you a program similar to the SOCAT example without reading a dummy port.

score 0 · Answer 7 · answered Jun 11 '20 at 11:15

You can use omping for this.

Example: To test multicast traffic between 3 hosts - execute then the same command line on each host:

omping example.org example.com example.net

Omping uses 192.168.178.79 by default but you can tell it to use any other multicast address.

If you snoop IGMP traffic you see the report (join) and leave messages then.

In contrast to socat omping also supports IPv6, in case you want to test MLD instead of IGMP.

Linux built-in or open source program to join multicast group?

7 Answers7