linux - multicast loopback in c -

i trying test multicast loopback clients join group , server multicast messgaes client in group constrained in 127.0.0.1 !!!!!

refering : http://www.tenouk.com/module41c.html , source :

the server :

struct in_addr localinterface; struct sockaddr_in groupsock; int sd; char databuf[1024] = "multicast test message lol!"; int datalen = sizeof(databuf);  int main (int argc, char *argv[ ]) {     /* create datagram socket on send. */     sd = socket(af_inet, sock_dgram, 0);     if(sd < 0)     {         perror("opening datagram socket error");         exit(1);     }     else         printf("opening datagram socket...ok.\n");      /* initialize group sockaddr structure */     /* group address of 225.1.1.1 , port 5555. */     memset((char *) &groupsock, 0, sizeof(groupsock));     groupsock.sin_family = af_inet;     groupsock.sin_addr.s_addr = inet_addr("224.0.0.0");     groupsock.sin_port = htons(4321);      /* disable loopback not receive own datagrams.      * {      * char loopch = 0;      * if(setsockopt(sd, ipproto_ip, ip_multicast_loop, (char *)&loopch, sizeof(loopch)) < 0)      * {      * perror("setting ip_multicast_loop error");      * close(sd);      * exit(1);      * }      * else      * printf("disabling loopback...ok.\n");      * }      * */      /* set local interface outbound multicast datagrams. */     /* ip address specified must associated local, */     /* multicast capable interface. */     localinterface.s_addr = inet_addr("127.0.0.1");     if(setsockopt(sd, ipproto_ip, ip_multicast_if, (char *)&localinterface, sizeof(localinterface)) < 0)     {         perror("setting local interface error");         exit(1);     }     else         printf("setting local interface...ok\n");      /* send message multicast group specified the*/     /* groupsock sockaddr structure. */     /*int datalen = 1024;*/     while( 1 ){         usleep( 1000 ) ;         if(sendto(sd, databuf, datalen, 0, (struct sockaddr*)&groupsock, sizeof(groupsock)) < 0)         {             perror("sending datagram message error");         }         else             printf("sending datagram message...ok\n");     }      /* try re-read socket if loopback not disable      * if(read(sd, databuf, datalen) < 0)      * {      * perror("reading datagram message error\n");      * close(sd);      * exit(1);      * }      * else      * {      * printf("reading datagram message client...ok\n");      * printf("the message is: %s\n", databuf);      * }      * */     return 0; } 

and client source :

struct sockaddr_in localsock; struct ip_mreq group; int sd; int datalen; char databuf[1024];  int main(int argc, char *argv[]) {     /* create datagram socket on receive. */     sd = socket(af_inet, sock_dgram, 0);     if(sd < 0)     {         perror("opening datagram socket error");         exit(1);     }     else         printf("opening datagram socket....ok.\n");      /* enable so_reuseaddr allow multiple instances of */     /* application receive copies of multicast datagrams. */     {         int reuse = 1;         if(setsockopt(sd, sol_socket, so_reuseaddr, (char *)&reuse, sizeof(reuse)) < 0)         {             perror("setting so_reuseaddr error");             close(sd);             exit(1);         }         else             printf("setting so_reuseaddr...ok.\n");     }      /* bind proper port number ip address */     /* specified inaddr_any. */     memset((char *) &localsock, 0, sizeof(localsock));     localsock.sin_family = af_inet;     localsock.sin_port = htons(4321);     localsock.sin_addr.s_addr = inaddr_any;     if(bind(sd, (struct sockaddr*)&localsock, sizeof(localsock)))     {         perror("binding datagram socket error");         close(sd);         exit(1);     }     else         printf("binding datagram socket...ok.\n");      /* join multicast group 226.1.1.1 on local 203.106.93.94 */     /* interface. note ip_add_membership option must */     /* called each local interface on multicast */     /* datagrams received. */     group.imr_multiaddr.s_addr = inet_addr("224.0.0.0");     group.imr_interface.s_addr = inet_addr("127.0.0.1");     if(setsockopt(sd, ipproto_ip, ip_add_membership, (char *)&group, sizeof(group)) < 0)     {         perror("adding multicast group error");         close(sd);         exit(1);     }     else         printf("adding multicast group...ok.\n");      /* read socket. */     datalen = sizeof(databuf);     while( 1 ){         if(read(sd, databuf, datalen) <= 0)         {             perror("reading datagram message error");             close(sd);             exit(1);         }         else         {             printf("reading datagram message...ok.\n");             printf("the message multicast server is: \"%s\"\n", databuf);         }     } //while      return 0; } 

after add following root , works fine :

route add -net 224.0.0.0 netmask 240.0.0.0 dev lo ifconfig lo multicast 

if have 1 client.exe running , perfect , , if run 2 copies of client.exe , server.exe or client.exe hang , if need more 1 application join group(in sample 224.0.0.0) , should modify source many clients may join muticast gruop , receive packets without troubles ?!