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Can a UDP socket be bound to same port number and different ip addresses

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anitha joe anitha joe is offline

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Can a UDP socket be bound to same port number and different ip addresses

-1

May 12th, 2009

Hello All,
I have a C program where I have created a UDP socket and bound to a particular ip address and a port number. As the program proceeds, msgs will be sent to different clients using the same socket, using the same port, but each has a different ip address. Is it possible to just overload the remoteServAddr1.sin_addr.s_addr with the desired ipaddress each time? Or is it important to bind the socket every time the ipaddress changes? If I call bind more than once, it gives me an error because the port is already in use.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
struct hostent *h;
	sd = socket(AF_INET,SOCK_DGRAM,0);
 		if(sd<0) 
		{
      			printf(" cannot open socket \n");
 
   		}
 
 
   		h = gethostbyname(address[0]); /*the first ip address*/
   		if(h==NULL) 
		{
      			printf("unknown host '%s' \n",  address[0]);
 
   		}
 
  		h->h_name,inet_ntoa(*(struct in_addr *)h->h_addr_list[0]));
 
   		remoteServAddr.sin_family = h->h_addrtype;
   		memcpy((char *) &remoteServAddr.sin_addr.s_addr, h->h_addr_list[0], h->h_length);
  		remoteServAddr.sin_port = htons(REMOTE_SERVER_PORT);
 
 
   		/* bind any port */
   		cliAddr.sin_family = AF_INET;
   		cliAddr.sin_addr.s_addr = htonl(INADDR_ANY);
   		cliAddr.sin_port = htons(REMOTE_SERVER_PORT);
 
   		rc = bind(sd, (struct sockaddr *) &cliAddr, sizeof(cliAddr));
 
   		if(rc<0) 
		{
     			printf("cannot bind port\n");
 
   		}
struct hostent *h;
	sd = socket(AF_INET,SOCK_DGRAM,0);
 		if(sd<0) 
		{
      			printf(" cannot open socket \n");
      
   		}

  	
   		h = gethostbyname(address[0]); /*the first ip address*/
   		if(h==NULL) 
		{
      			printf("unknown host '%s' \n",  address[0]);
     
   		}

  		h->h_name,inet_ntoa(*(struct in_addr *)h->h_addr_list[0]));

   		remoteServAddr.sin_family = h->h_addrtype;
   		memcpy((char *) &remoteServAddr.sin_addr.s_addr, h->h_addr_list[0], h->h_length);
  		remoteServAddr.sin_port = htons(REMOTE_SERVER_PORT);

  
   		/* bind any port */
   		cliAddr.sin_family = AF_INET;
   		cliAddr.sin_addr.s_addr = htonl(INADDR_ANY);
   		cliAddr.sin_port = htons(REMOTE_SERVER_PORT);
  
   		rc = bind(sd, (struct sockaddr *) &cliAddr, sizeof(cliAddr));

   		if(rc<0) 
		{
     			printf("cannot bind port\n");
   
   		}

I want to change the ipaddress which will be stored as address[1]..So rather than address[0] in the above code, I want address[1]( socket,port being the same)..

Something like this

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 c Syntax (Toggle Plain Text) 
memcpy((char *) &remoteServAddr.sin_addr.s_addr, address[1], h1->h_length);
accept(sd, (struct sockaddr *)(&remoteServAddr), &cliLen);
printf("sending %s to %s on UDP port %u \n",connection,inet_ntoa(remoteServAddr.sin_addr), ntohs(remoteServAddr1.sin_port));
   rc = sendto(sd,connection,MAX_MSG, 0,(struct sockaddr *) &remoteServAddr, sizeof(remoteServAddr));
memcpy((char *) &remoteServAddr.sin_addr.s_addr, address[1], h1->h_length);
accept(sd, (struct sockaddr *)(&remoteServAddr), &cliLen);
printf("sending %s to %s on UDP port %u \n",connection,inet_ntoa(remoteServAddr.sin_addr), ntohs(remoteServAddr1.sin_port));
   rc = sendto(sd,connection,MAX_MSG, 0,(struct sockaddr *) &remoteServAddr, sizeof(remoteServAddr));

Is it possible at all??Any help would be appreciated..Right now its giving segmentation fault...
Thanks
Ani

Last edited by Narue; May 14th, 2009 at 12:24 pm. Reason: added code tags

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jephthah

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Re: Can a UDP socket be bound to same port number and different ip addresses

May 13th, 2009

maybe i'm missing something, but UDP doesn't care what IP address is in the pseudo-header. it's a multicast protocol. anyone on the network can see and process the datagrams if they desire to do so.