MCAST_JOIN_SOURCE_GROUP and MCAST_LEAVE_SOURCE

Use the MCAST_JOIN_SOURCE_GROUP option to set the IPv4 or IPv6 multicast address, source address, and the local interface index. Use the SETSOCKOPT API and specify the address of the GROUP_SOURCE_REQ structure that contains these addresses and the interface index. The application can join multiple source multicast groups on a single socket and can also join the same group on multiple interfaces on the same socket. However, there is a maximum limit of 20 groups per single UDP socket and there is a maximum limit of 256 groups per single RAW socket. The stack chooses a default multicast interface if the interface index 0 is passed. The format of the GROUP_SOURCE_REQ structure is in the BPXYSOCK macro. The assembler program example in Figure 1 shows this socket option using the EZASMI macro:

Figure 1. MCAST_JOIN_SOURCE_GROUP and MCAST_LEAVE_SOURCE_GROUP

    ***********************************************************************
    *                                                                     *
    *        Issue SETSOCKOPT - MCAST_JOIN_SOURCE_GROUP                   *
    *                                                                     *
    ***********************************************************************
              
             EZASMI TYPE=SETSOCKOPT,  ISSUE SETSOCKOPT                     X
                   S=S,               SOCKET DESCRIPTOR                    X
                   OPTLEN=OPTL264,    OPTION LENGTH                        X
                   OPTNAME='MCAST_JOIN_SOURCE_GROUP', OPTION NAME          X
                   OPTVAL=GSR_REQ1,   OPTION VALUE                         X
                   ERRNO=ERRNO,       (SPECIFY ERRNO FIELD)                X
                   RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X
                   ERROR=ERROR        ABEND IF MACRO ERROR
             BAL   R14,RCCHECK         --> CHECK IT
    *
    * Here your program will perform normal processing such as sending or
    * receiving message.
    *

    ***********************************************************************
    *                                                                     *
    *        Issue SETSOCKOPT - MCAST_LEAVE_SOURCE_GROUP                  *
    *                                                                     *
    ***********************************************************************
              
             EZASMI TYPE=SETSOCKOPT,  ISSUE SETSOCKOPT                     X
                   S=S,               SOCKET DESCRIPTOR                    X
                   OPTLEN=OPTL264,    OPTION LENGTH                        X
                   OPTNAME='MCAST_LEAVE_SOURCE_GROUP', OPTION NAME         X
                   OPTVAL=GSR_REQ1,   OPTION VALUE                         X
                   ERRNO=ERRNO,       (SPECIFY ERRNO FIELD)                X
                   RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X
                   ERROR=ERROR        ABEND IF MACRO ERROR
             BAL   R14,RCCHECK         --> CHECK IT

To remove the host from the source multicast host group you must issue a SETSOCKOPT call with the MCAST_LEAVE_SOURCE_GROUP option. This call is similar to the MCAST_JOIN_SOURCE_GROUP option because it also uses the GROUP_SOURCE_REQ structure to declare the IPv4 or IPv6 multicast address, source address, and the local interface index (see Figure 1). You can also use the MCAST_LEAVE_GROUP option to remove all sources for a given multicast group.

While the application is a member of the source multicast host group, datagrams can be sent or received as required. To see the multicast groups that are joined on an interface, use the Netstat DEvlinks/-d command. To see the multicast groups that are joined on a socket, use the Netstat ALL/-A command.