Multicast help needed.

Multicast help needed.

Post by chin.. » Sat, 24 Jun 2000 04:00:00


      I need some help in fully understanding multicast. For an
application to receive multicast packets it first has to bind to a port
and then add membership to the multicast group. Is this right.

      Here is my setup - A machine with one IP interface and one
address (IP1).

      Here is what I did -

      1) Open a socket.
      2) Bind the socket with address IP1, port1.
      3) Set socket options to add multicast membership to multicast
address MADDR1.
         The ip_mreq structure is filled as
         struct ip_mreq mreq;
         mreq.imr_interface.s_addr = htonl(IP1);
         mreq.imr_multiaddr.s_addr = htonl(MADDR1);
      4) I send a packet with the destination address as MADDR1 and
port port1.

      I dont get any data on this socket. If I change the address IP1
in step 2 to INADDR_ANY then I receive the packet. Why dont I receive
the packet in the first case.

     My second question.

     I have a machine with two IP interfaces. The two IP interfaces are
on seperate LAN's. I want to open one server per interface and listen
to multicast packets only on that interface. What is the best way to do



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