Name & Address Conversions

Ø Domain Name Servers

Ø Basic Functions

Ø Support for both IPv4 and IPv6

Ø Example of Protocol-Independent Client:

Ø Domain Name Servers

ü File:  /etc/resolv.conf
contains the IP addresses of the local name servers

ü File:  /etc/services
contains the names and ports of services.

Ø Basic Functions

ü gethostbyname

&

ü gethostbyaddr

ª Hosent struct

h_name (official name)
h_aliases
h_addr_list

à Example: GetHostInfo.c

% cd /home/cs779/stevens3rd.book/unpv13e/names

% GetHostInfo fast cnn.com 128.82.4.210  mail  ftp  www 

à GetHostInfo.c
 
Code Outline:
 . . . . 
 if ( (inetaddr = inet_addr(ptr)) != -1){
 if ((hptr = gethostbyaddr((char *)&inetaddr, sizeof(inetaddr), AF_INET)) == NULL) {
 printf("\t(gethostbyaddr failed %s)\n", ptr);
 continue;
 }
 } else{
 if ( (hptr = gethostbyname(ptr)) == NULL) {
  printf("\t(gethostbyname failed %s)\n", ptr);
 continue;
 }
 }
 printf("official hostname: %s\n", hptr->h_name);
 for (pptr = hptr->h_aliases; *pptr != NULL; pptr++)
 printf("\talias: %s\n", *pptr);
 switch (hptr->h_addrtype) {
  case AF_INET:
 pptr = hptr->h_addr_list;
 for ( ; *pptr != NULL; pptr++)
 printf("\taddress: %s\n", inet_ntop(hptr->h_addrtype, *pptr, str, sizeof(str)));
 break;
 . . . .
 

à Example: daytimetcpcli2.c

% daytimetcpsrv1 10313

% daytimetcpsrv1 daytime // must be root, since daytime port is 13

% daytimetcpcli2 128.82.4.210 10313
% daytimetcpcli2 something 10313
% daytimetcpcli2 128.82.4.210 daytime
% daytimetcpcli2  something daytime

% daytimetcpcli2 fast 10313 // try connecting to all fast aliases.

ª Other Functions getipnodebyname   & getipnodebyaddr.pdf

Ø Support for both IPv4 and IPv6

ª Latest Functions

getaddrinfo   & getnameinfo

ª Addrinfo struct

à Example: GetGenHostInfo.c

% cd /home/cs779/stevens3rd.book/unpv13e/names

% GetGenHostInfo fast cnn.com 128.82.4.210  mail  ftp  www

% GetGenHostInfo fe80::203:baff:fe2a:ab9b  

à GetGenHostInfo.c

. . . .

 if ( (n = getaddrinfo(ptr, NULL, &hints, &res)) != 0)
  err_quit("udp_server error for %s: %s", ptr, gai_strerror(n));
 
 do{
 
 if (res->ai_canonname)
 printf("ai_canonname = %s\n", res->ai_canonname);
 
 printf("address:(%s) %s\n",str_fam(res->ai_family), 
  Sock_ntop(res->ai_addr, res->ai_addrlen));
 
 
 
 rc = getnameinfo(res->ai_addr, res->ai_addrlen, rhost, 
 NI_MAXHOST, NULL, NULL, NI_NAMEREQD);
 if (rc == 0) {
 printf("getnameinfo: host = %s\n", rhost );
 } else
 printf("getnameinfo returned %d (%s)\n", rc, gai_strerror(rc));
 
  } while ( (res = res->ai_next) != NULL);
 
 

Ø Example of Protocol-Independent Client:

à cgu.c (c4u+c6u) - client general (4+6) udp:

 
  . . . 
 
 struct sockaddr_storage servaddr;
 struct addrinfo hints, *res;
 
 
 bzero(&hints, sizeof(struct addrinfo));
 hints.ai_family = AF_UNSPEC;
 hints.ai_socktype = SOCK_DGRAM;
 
 
 getaddrinfo(argv[1], "1313", &hints, &res);
 
 sockfd = socket(res->ai_family, SOCK_DGRAM, 0);
 
 connect(sockfd, (SA *)res->ai_addr, res->ai_addrlen); 
 

. . .

ü Testing:

something % cd /home/cs779/stevens3rd.book/unpv13e/intro

something % s6u &

something % cgu fe80::203:baff:fe2a:67ff

something % cgu 128.82.4.210

//replace s6u with s4u:

something % s4u &

something % cgu 128.82.4.210

something % cgu ::ffff:128.82.4.210