IPv6 Socket Programming
2004.10.6
Joonbok Lee
KAIST
Contents
1. Socket
2. IPv6
3. IPv6 Socket Programming
1. Socket
1.1 What is a socket?
• Socket
– The combination of an IP address and a port number. (RFC
793 ,original TCP specification)
– The name of the Berkeley-derived application programming
interfaces (APIs) for applications using TCP/IP protocols.
– Two types
• Stream socket : reliable two-way connected communication streams
• Datagram socket
• Socket pair
– Specify the two end points that uniquely identifies each TCP
connection in an internet.
– 4-tuple: (client IP address, client port number, server IP address,
server port number)
1.2 Client-server applications
• Implementation of a protocol standard defined in an RFC. (FTP,
HTTP, SMTP…)
– Conform to the rules dictated by the RFC.
– Should use the port number associated with the protocol.
• Proprietary client-server application.
– A single developer( or team) creates both client and server
program.
– The developer has complete control.
– Must be careful not to use one of the well-known port number
defined in the RFCs.
* well-known port number : managed by the Internet Assigned
Numbers Authority(IANA)
1.3 Socket Programming with TCP
Figure 2.6-1: Processes communicating through TCP sockets
The application developer has the ability to fix a few TCP parameters,
such as maximum buffer and maximum segment sizes.
1.4 Sockets
Figure 2.6-2: Client socket, welcoming socket and connection socket
1.5 Sockets for server and client
• Server
– Welcoming socket
• Welcomes some initial contact from a client.
– Connection socket
• It is created at initial contact of client.
• New socket that is dedicated to the particular client.
• Client
– Client socket
• Initiate a TCP connection to the server by creating a socket
object. (Three-way handshake)
• Specify the address of the server process, namely, the IP
address of the server and the port number of the process.
1.6 Socket Programming- TCP
server
client
socket( )
bind( )
connect( )
send( )
socket( )
bind( )
listen( )
TCP conn. request
TCP ACK
accept( )
recv( )
recv( )
close( )
send( )
close( )
2. IPv6
2.1 IPv4 and IPv6
• IPv4
– RFC 791, which was published in 1981
– 32bit address space: 4,294,967,296 (232) addresses
• IPv6
– 128bit address space: 3.4 x 1038
• 67billion billion addresses per cm2 of the planet space.
–
–
–
–
Hierarchical address architecture
Security (built-in IPsec)
Autoconfiguration
IETF IPv6 Working Group
2.2 IPv6 Address
• RFC 2373
• x:x:x:x:x:x:x:x (x is 16bit)
ex) 3ffe:8041:2:1:bc16:6ee6:26ab:7ba8
• ‘::’ indicates multiple groups of 16 bits of zeros.
ex) 3ffe:8041:0:0:0:0:0:3  3ffe:8041::3
• IPv6 Address Structure: Prefix + Interface ID
ex) 3ffe:8041:2:1:bc16:6ee6:26ab:7ba8/64
2.3 Example
eth0
Link encap:Ethernet HWaddr 00:04:76:2F:CC:34
inet addr:134.75.85.132 Bcast:134.75.255.255 Mask:255.255.255.224
inet6 addr: 2001:320:1a10:3:204:76ff:fe2f:cc34/64 Scope:Global
inet6 addr: fe80::204:76ff:fe2f:cc34/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1595908 errors:0 dropped:0 overruns:0 frame:0
TX packets:24722783 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1091245010 (1040.6 Mb) TX bytes:1288208803 (1228.5 Mb)
Interrupt:177
3. IPv6 Socket Programming
3.1 Goal
• Develope IPv6-aware (or IPv6-enable) application.
• Application Type
– IPv4-only: not able to handle IPv6 addresses
– IPv6-aware: can communicate with nodes that do not have
IPv4 addresses
– IPv6-enable: in addition to being IPv6-aware, takes
advantage of some IPv6 specific features such as flow labels
– IPv6-required: requires some IPv6 specific feature and
therefore cannot operate over IPv4
3.2 Changes socket API for IPv6 Support
• New socket address structure to carry IPv6 address
• New address conversion functions and several new
socket options
• RFC 3493
3.3 Typical IPv6 Code sequence
• Same with IPv4
– Server
•
•
•
•
•
•
Socket – open a socket
Bind – bind our local address to the socket
Listen – tell that we are listening to a port
Accept – wait for connection
Read and/or write if TCP
Recvfrom and/or sendto if UDP
– Client
•
•
•
•
Socket – open a socket
Connect – connect to the server
Read and/or write if TCP
Recvfrom and/or sendto if UDP
3.4 What need to be changed
• Socket Interface
– New protocol family name: PF_INET6
• Address data structures
– Net address family name: AF_INET6
– in6_addr structure
– sockaddr_in6 structure
• Name-to-address translation functions
– inet_pton, inet_ntop
• Address conversion functions
– getnameinfo
– getaddrinfo
3.5 IPv6-enable application example
Client
int main(int argc, char **argv){
char Buffer[BUFFER_SIZE];
char *Server = DEFAULT_SERVER;
/* “143.248.226.231”
“2001:320:1a10:3:204:76ff:fe2f:cc34”
“cosmos.kaist.ac.kr” */
int Family = DEFAULT_FAMILY;
/* AF_INET, AF_INET6, AF_UNSPEC */
int SocketType = DEFAULT_SOCKTYPE;
/* SOCK_STREAM, SOCK_DGRAM, SOCK_RAW, … */
char *Port = DEFAULT_PORT;
int i, RetVal, AddrLen, AmountToSend;
struct addrinfo Hints, *AddrInfo, *AI;
socket ConnSocket;
struct sockaddr_storage Addr;
memset(&Hints, 0, sizeof(Hints));
Hints.ai_family = AF_UNSPEC;
/* AF_INET: IPv4 address, AF_INET6: IPv6 address, AF_UNSPEC: IPv4 and IPv6 address */
Hints.ai_socktype = SOCK_STREAM;
/* SOCK_STREAM: TCP, SOCK_DGRAM: UDP */
RetVal = getaddrinfo(Server, Port, &Hints, &AddrInfo);
if (RetVal != 0) {
fprintf(stderr, "Cannot resolve address [%s] and port [%s], error %d: %s\n", Server, Port, RetVal,
gai_strerror(RetVal));
return -1;
}
for (AI = AddrInfo; AI != NULL; AI = AI->ai_next) {
// Open a socket with the correct address family for this address.
// if( AI->ai_family == AF_INET6 ){
ConnSocket = socket(AI->ai_family, AI->ai_socktype, AI-> ai_protocol);
if (ConnSocket == INVALID_SOCKET) continue;
if (connect(ConnSocket, AI->ai_addr, AI->ai_addrlen) != SOCKET_ERROR) break;
// }
}
freeaddrinfo(Addrinfo);
strcpy(Buffer, “Hello, world”);
AmmountToSend = strlen(Buffer);
RetVal = send(ConnSocket, Buffer, AmmountToSend, 0);
RetVal = recv(ConnSocket, Buffer, Buffer, BUFFER_SIZE, 0);
closesocket(ConnSocket);
}
Server
#define MAXSOCK 2
struct addrinfo hints, *res;
struct sockaddr_storage from;
int error, sockfd[MAXSOCK], nsock=0, connsock, fromlen;
memset(&hints, 0, sizeof(hints));
hints.ai_flags = AI_PASSIVE;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
error = getaddrinfo(NULL, SERVICE, &hints, &res);
if (error != 0) {
/* handle getaddrinfo error */
}
for (aip=res; aip && nsock < MAXSOCK; aip=aip->ai_next) {
sockfd[nsock] = socket(aip->ai_family, aip->ai_socktype, aip->ai_protocol);
if (sockfd[nsock] < 0) {
/* handle socket error */
}
}
else {
int on = 1;
/* optional: works better if dual-binding to wildcard address */
if (aip->ai_family == AF_INET6) {
setsockopt(sockfd[nsock], IPPROTO_IPV6, IPV6_V6ONLY, (char *)&on,
sizeof(on));
/* errors are ignored */
}
if (bind(sockfd[nsock], aip->ai_addr, aip->ai_addrlen) < 0 ) {
/* handle bind error */
close(sockfd[nsock]);
continue;
}
if (listen(sockfd[nsock], SOMAXCONN) < 0) {
/* handle listen errors */
close(sockfd[nsock]);
continue;
}
nsock++;
}
freeaddrinfo(res);
/* check that we were able to obtain the sockets */
/*select socket and close other socket*/
fromlen = sizeof(from);
connsock = accept(selectedsock, &from, fromlen);
/* handle accept error */
ammountread = recv(connsock, buffer, sizeof(buffer), 0);
/* handle recv error */
send(connsock, buffer, ammountread, 0);
/* handle send error */
closesocket(connsock);
}
3.6 Concurrent server
• Servers need to handle a new connection request
while processing previous requests.
– Most TCP servers are designed to be concurrent.
• When a new connection request arrives at a server,
the server accepts and invokes a new process to
handle the new client.
Appendix IPv6 Support
• Linux: Kernel 2.4.x
– http://cosmos.kaist.ac.kr/~shlee/ipv6/doc/ipv6linux.txt
• Windows XP, windows 2000, windows 2003
– http://www.microsoft.com/windowsserver2003/technologies
/ipv6/default.mspx