I want to write a linux shell script which will capture specific multicast traffic.  Specific as in, I want to create a pcap file that has all the traffic for one specific multicast group/port.Here is the command line I am using to view traffic:tcpdump -nnXs 0 -i eth1 udp port 22001 and dst 233.54.12.234This works fine so long as I have a multicast subscription to that group already established.  For example, if I run this in another console:mdump 233.54.12.234 22001 10.13.252.51tcpdump will see packets.  If mdump is not running, tcpdump sees nothing.Is there a standard linux-y way to establish these multicast joins before starting the captures?  I could use mdump to establish these joins, but that seems wasteful since mdump will process all that data on the group, bbut I'm just going to throw it away.Note that because my specific environment, I have been discouraged from putting the interface in to promiscuous mode.  It may, in fact, be prohibited.
Creating multicast join for tcpdump captures
linux;shell script;tcpdump;multicast