multicast tcpdump and subscriptions
- by Karoly Horvath
From the multicast howto:
IP_ADD_MEMBERSHIP.
Recall that you need to tell the kernel which multicast groups you are interested
in. If no process is interested in a group, packets destined to it that arrive to
the host are discarded.
If you don't do that, you won't see those packets with tcpdump.
Is it possible to subscribe to all multicast traffic so I can do a tcpdump for all existing traffic? I would think IGMP doesn't allow this, so probably not.. but maybe you can configure a switch to still send all multicast traffic. Is that possible?
Is it possible to do subscription (for a specific IP) with a command line tool? (note: I know how to do this in C.. but would prefer to use an existing tool and not compile a separate program for this)
