This document discusses different combinations of IPv4 and IPv6 clients and servers and how they can communicate. It covers: - An IPv6 dual stack server that can handle both IPv4 and IPv6 clients using IPv4-mapped IPv6 addresses. - An IPv6 client connecting to an IPv4 server by using IPv4-mapped addresses returned by gethostbyname. - Macros and socket options for determining address types and converting between IPv4 and IPv6 sockets. - Using getaddrinfo and getnameinfo for more portable source code across IPv4 and IPv6.

1. Presented by R P Porwal

2. contents
 Introduction
 IPv4 Client, IPv6 Server
 IPv6 Client, IPv4 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
client
IPv6
server
TCP
IPv6
Data
link
Data
link
IPv4
TCP
IPv4
client
TCP
IPv4 IPv6
Data
link
Enet
hdr
IPv4
hdr
TCP
hdr
TCP
data
Enet
hdr
IPv4
hdr
TCP
hdr
TCP
data
Type0800
Type0800 Dport 8888
Dport 8888
206.62.226.42
IPv4 mapped
IPv6 address
IPv6 listening socket,
bound to 0::0, port 8888
IPv6 address
5flb:df00:ce3
e:e200:20:80
0:2b37:6426

6. IPv4 datagram IPv6 datagram
AF_INET
SOCK_STREAM
sockaddr_in
AF_INET
SOCK_DGRAM
sockaddr_in
AF_INET6
SOCK_DGRAM
sockaddr_in6
AF_INET6
SOCK_DGRAM
sockaddr_in6
TCP
IPv4 IPv6
UDP
IPv4
sockets
IPv6
sockets
Address
returned by
accept or
recvfrom
IPv6IPv4
IPv4 mapped

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 datagram IPv6 datagram
AF_INET
SOCK_STREAM
sockaddr_in
AF_INET
SOCK_DGRAM
sockaddr_in
AF_INET6
SOCK_DGRAM
sockaddr_in6
AF_INET6
SOCK_DGRAM
sockaddr_in6
TCP
IPv4 IPv6
UDP
IPv4
sockets
IPv6
sockets
Address
for connect
or sendto
IPv6IPv4
IPv4 mappedIPv6

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. 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);
Converting an IPv4 to IPv6

12.  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