Chapter 10 IPv4 and IPv6 Interoperability

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

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

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

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 206.62.226.42 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

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

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

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

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)

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.

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);

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

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