IP_MULTICAST

The API uses IP_MULTICAST_LOOP socket option to enable or disable the loopback of outgoing multicast datagrams. The default is enabled. This option is used to enable an application with multiple senders and receivers on a system to loop datagrams back so that each process receives the transmissions of the other senders on the system. Figure 1 illustrates the use of IP_MULTICAST_IF by the use of the SETSOCKOPT and GETSOCKOPT APIs.

Figure 1. IP_MULTICAST_LOOP

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*                                                                     *  
*        Issue SETSOCKOPT/GETSOCKOPT - IP_MULTICAST_LOOP ENABLED      *  
*                                                                     *  
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         EZASMI TYPE=SETSOCKOPT,  ISSUE SETSOCKOPT                     X 
               S=S,               SOCKET DESCRIPTOR                    X 
               OPTLEN=OPTLEN1,    OPTION LENGTH                        X 
               OPTNAME='IP_MULTICAST_LOOP', OPTION NAME                X 
               OPTVAL=OPTVALON,   OPTION VALUE                         X 
               RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X 
               ERROR=ERROR        ABEND IF MACRO ERROR
         BAL   R14,RCCHECK         --> CHECK IT                         
*
         XC    OPTVAL4,OPTVAL4                                           
         EZASMI TYPE=GETSOCKOPT,  ISSUE GETSOCKOPT                     X 
               S=S,               SOCKET DESCRIPTOR                    X 
               OPTLEN=OPTLEN1,    OPTION LENGTH                        X 
               OPTNAME='IP_MULTICAST_LOOP', OPTION NAME                X 
               OPTVAL=OPTVAL4,    OPTION VALUE                         X 
               RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X 
               ERROR=ERROR        ABEND IF MACRO ERROR
         BAL   R14,RCCHECK         --> CHECK IT

***********************************************************************  
*                                                                     *  
*        Issue SETSOCKOPT/GETSOCKOPT - IP_MULTICAST_LOOP DISABLED     *  
*                                                                     *  
***********************************************************************  
         EZASMI TYPE=SETSOCKOPT,  ISSUE SETSOCKOPT                     X 
               S=S,               SOCKET DESCRIPTOR                    X 
               OPTLEN=OPTLEN1,    OPTION LENGTH                        X 
               OPTNAME='IP_MULTICAST_LOOP', OPTION NAME                X 
               OPTVAL=OPTVALOFF,  OPTION VALUE                         X 
               RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X 
               ERROR=ERROR        ABEND IF MACRO ERROR
         BAL   R14,RCCHECK         --> CHECK IT    
         XC    OPTVAL4,OPTVAL4                    
         EZASMI TYPE=GETSOCKOPT,  ISSUE GETSOCKOPT                     X 
               S=S,               SOCKET DESCRIPTOR                    X 
               OPTLEN=OPTLEN1,    OPTION LENGTH                        X 
               OPTNAME='IP_MULTICAST_LOOP', OPTION NAME                X 
               OPTVAL=OPTVAL4,    OPTION VALUE                         X 
               RETCODE=RETCODE,   (SPECIFY RETCODE FIELD)              X 
               ERROR=ERROR        ABEND IF MACRO ERROR 
         BAL   R14,RCCHECK         --> CHECK IT