The document discusses programming with IPv6 by providing examples of echo clients and servers for both IPv4 and IPv6. It outlines refining applications to support both protocols, including handling DNS conversions and special cases for IPv4-only or IPv6-only environments. Key functions mentioned are gethostbyname, gethostbyaddr, gethostbyname2, and sockets calls for IPv4 and IPv6. The hostent and addrinfo structures are also covered.

1. IPv6 Programming
Eric 2012/06/29

2. outline
echo client
echo server
DNS conversions
refine our app to support ipv6 and ipv4
special case

3. ipv4 echo client
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in serv_addr;
memset((unsigned char *)&serv_addr, 0x00, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(9999);
inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr);
connect(sock, (struct sockaddr *)&serv_addr,
sizeof(serv_addr));

4. ipv6 echo client
int sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in6 serv_addr;
memset((unsigned char *)&serv_addr, 0x00, sizeof(serv_addr));
serv_addr.sin6_family = AF_INET6;
serv_addr.sin6_port = htons(9999);
inet_pton(AF_INET6, "::1", &serv_addr.sin6_addr);
connect(sock, (struct sockaddr *)&serv_addr,
sizeof(serv_addr));

5. comparison

6. ipv4 echo server
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in serv_addr;
memset((unsigned char *)&serv_addr, 0x00, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(9999);
serv_addr.sin_addr.s_addr = INADDR_ANY;
struct sockaddr_in client_addr;
bind(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
listen(sock, 20);
socklen_t len = sizeof(client_addr);
int conn = accept(sock, (struct sockaddr *)&client_addr,
&len);

7. ipv6 echo server
int sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in6 serv_addr;
memset((unsigned char *)&serv_addr, 0x00, sizeof(serv_addr));
serv_addr.sin6_family = AF_INET6;
serv_addr.sin6_port = htons(9999);
serv_addr.sin6_addr = in6addr_any;
const int on = 1;
setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on));
struct sockaddr_in6 client_addr;
bind(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
listen(sock, 20);
socklen_t len = sizeof(client_addr);
int conn = accept(sock, (struct sockaddr *)&client_addr,
&len);

8. ipv4 & ipv6 echo server
let’s see echoServer2.c
set up 2 socket for ipv4 and ipv6
independently.
select is key point.

9. DNS conversions
please notice following functions:
gethostbyname
gethostbyaddr
gethostbyname2
inet_aton, inet_ntoa
let’s see hostent.c

10. hostent structure

11. addrinfo structure

12. refine our app to
support ipv6 and ipv4
grep -re “gethostby” *
grep -re “inet_ntoa” *
grep -re “inet_aton” *
grep -re “AF_INET” *
grep -re “sockaddr_in” *

13. special case
if our environment support ipv4 and ipv6, so
server is simple
ipv4 -> ipv4 socket
ipv6 -> ipv6 socket
const int on = 1;
setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY,
&on, sizeof(on));

14. special case
if our environment support ipv4 and ipv6, so
client must consider priority of DNS
conversions and retry connection.

15. special case
but......
if our environment is ipv4 only, we should
use hints.ai_family = AF_INET on
getaddrinfo.
relatively, env is ipv6 only, please enable
hints.ai_family = AF_INET6 on getaddrinfo.

16. Thanks a lot.