j'ai pulseaudio qui diffuse un flux en multicast :
$ sudo tcpdump -n net 224.0.0.0/8 -c 10
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
00:58:12.486334 IP 192.168.1.21.48338 > 224.0.0.56.46056: UDP, length 1284
00:58:12.486343 IP 192.168.1.21.48338 > 224.0.0.56.46056: UDP, length 1284
00:58:12.486547 IP 192.168.1.21.48338 > 224.0.0.56.46056: UDP, length 1284
00:58:12.486554 IP 192.168.1.21.48338 > 224.0.0.56.46056: UDP, length 1284
00:58:12.496220 IP 192.168.1.21.48338 > 224.0.0.56.46056: UDP, length 1284
(…)