1. Chapter 10 IPv4 and IPv6 Interoperability

2. contents Introduction IPv4 Client, IPv6 Server
IPv6 Address Testing Macros
IPV6_ADDRFORM Socket Option
Source Code Portability

3. Introduction Server and client combination
IPv4 <=> IPv4(most server and client)
IPv4 <=> IPv6
IPv6 <=> IPv4
IPv6 <=> IPv6
How IPv4 application and IPv6 application can communicate with each other.
Host are running dual stacks, both an IPv4 protocol stack and IPv6 protocol stack

4. IPv4 Client , IPv6 Server
IPv6 dual stack server can handle both IPv4 and IPv6 clients.
This is done using IPv4-mapped IPv6 address
server create an IPv6 listening socket that is bound to the IPv6 wildcard address

5. IPv6 server IPv6 client IPv4 client TCP TCP TCP IPv6 IPv4 IPv4 IPv6
IPv6 listening socket,
bound to 0::0, port 8888
TCP
TCP
TCP
IPv6 address
IPv4 mapped IPv6 address
IPv6
IPv4
IPv4
IPv6
5flb:df00:ce3e:e200:20:800:2b37:6426
Data
link
Data
link
Data
link
Enet
hdr
IPv4
hdr
TCP
hdr
TCP
data
Type0800
Dport 8888
TCP
hdr
TCP
data
Enet
hdr
IPv4
hdr
Type0800
Dport 8888

6. IPv4 sockets IPv6 sockets AF_INET SOCK_DGRAM sockaddr_in AF_INET
SOCK_STREAM
sockaddr_in
IPv4 sockets
AF_INET6
SOCK_DGRAM
sockaddr_in6
AF_INET6
SOCK_DGRAM
sockaddr_in6
IPv6
sockets
UDP
TCP
IPv4 mapped
IPv4
IPv6
Address
returned by
accept or
recvfrom
IPv4
IPv6
IPv4 datagram
IPv6 datagram

7. IPv6 client, IPv4 server
IPv4 server start on an IPv4 only host and create an IPv4 listening socket
IPv6 client start, call gethostbyname. IPv4 mapped IPv6 address is returned.
Using IPv4 datagram

8. IPv4 sockets IPv6 sockets AF_INET SOCK_DGRAM sockaddr_in AF_INET
SOCK_STREAM
sockaddr_in
IPv4 sockets
AF_INET6
SOCK_DGRAM
sockaddr_in6
AF_INET6
SOCK_DGRAM
sockaddr_in6
IPv6
sockets
UDP
TCP
IPv6
IPv4 mapped
IPv4
IPv6
Address
for connect
or sendto
IPv4
IPv6
IPv4 datagram
IPv6 datagram

9. IPv6 Address Testing Macros
There are small class of IPv6 application that must know whether they are talking to an IPv4 peer.
These application need to know if the peer’s address is an IPv4-mapped IPv6 address.
Twelve macro defined(참조 page 267)

10. IPV6_ADDRFORM Socket Option
Can change a socket from one type to another, following restriction.
An IPv4 socket can always be changed to an IPv6. Any IPv4 address already associated with the socket are converted to IPv4- mapped IPv6 address.
An IPv6 socket can changed to an IPv4 socket only if any address already associated with the socket are IPv4-mapped IPv6 address.

11. Converting an IPv4 to IPv6
Int af;
socklen_t clilen;
struct sockaddr_int6 cli; /* IPv6 struct */
struct hostent *ptr;
af = AF_INT6;
Setsockopt(STDIN_FILENO, IPPROTO_IPV6, IPV6_ADDRFORM, &af, sizeof(af));
clilen = sizeof(cli);
Getpeername(0, &cli, &clilen);
ptr = gethostbyaddr(&cli.sin6_addr, 16, AF_INET);

12. getpeername =>return an IPv4-mapped IPv6 address
setsockopt => change the Address format of socket from IPv4 to IPv6.
Return value is AF_INET or AF_INET6
getpeername =>return an IPv4-mapped IPv6 address

13. Source Code Portability
#ifdefs => hard to maintain, littered …
use getaddrinfo and getnameinfo