1. Chapter 3 Sockets Introduction
By They Yu Shu

2. Outline Socket Address Structures Value-Result Arguments
Byte Ordering Functions
Byte Manipulation Functions
Address Conversion

3. Socket Address Structure
In socket programming, IP address and Port value are used to identify the end-points of the TCP/IP communication.
Socket Address Structure is a data structure to hold
Address Family
IP address
Port Value
And ….

4. IPv4 Socket Address Structure
struct in_addr {
in_addr_t s_addr; /* 32-bit IPv4 address */
/* network byte ordered */ };
struct sockaddr_in {
uint8_t sin_len; /* length of structure */
sa_family_t sin_family; /* 16 bit address family*/
/*AF_INET*/
in_port_t sin_port; /* 16-bit TCP or UDP port number */
struct in_addr sin_addr; /* 32-bit IPv4 address */
char sin_zero[8]; /* unused (to keep sockaddr_in > 16 bytes in size) */

5. Address Family Number Number Description Reference
0 Reserved
1 IP (IP version 4)
2 IP6 (IP version 6)
3 NSAP
4 HDLC (8-bit multidrop)
5 BBN 1822
(includes all 802 media plus Ethernet "canonical format")
7 E.163
8 E.164 (SMDS, Frame Relay, ATM)
9 F.69 (Telex)
10 X.121 (X.25, Frame Relay)
11 IPX
12 Appletalk
13 Decnet IV
14 Banyan Vines
15 E.164 with NSAP format subaddress [UNI-3.1] [Malis]
16 DNS (Domain Name System)
17 Distinguished Name [Lynn]
18 AS Number [Lynn]
19 XTP over IP version [Saul]
20 XTP over IP version [Saul]
21 XTP native mode XTP [Saul]
22 Fibre Channel World-Wide Port Name [Bakke]
23 Fibre Channel World-Wide Node Name [Bakke]
24 GWID [Hegde]
25 AFI for L2VPN information [RFC4761]
Reserved

6. Socket Functions IPv4 Socket Address Structure IPv6 Socket
others Socket
Address Structure
Socket Functions:
Bind()
Connect()
Send()
Recv() ….
Example: int bind(int, struct sockaddr *, socklen_t );

7. Generic Socket Address Structure
struct sockaddr {
uint8_t sa_len;
sa_family_t sa_family; /* address family: AF_xxx value */
char sa_data[14]; /* protocol-specific address */ };

8. Using Generic Socket Address Structure
struct sockaddr_in serv;
/* IPv4 socket address structure */
/* fill in serv{} */
bind(sockfd, (struct sockaddr *) &serv, sizeof(serv));

9. IPv6 Socket Address Structure
struct in6_addr {
uint8_t s6_addr[16]; /* 128-bit IPv6 address */
/* network byte ordered */ };
struct sockaddr_in6 {
uint8_t sin6_len; /* length of this struct (28) */
sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* transport layer port# */
uint32_t sin6_flowinfo; /* flow information, undefined */
struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* set of interfaces for a scope */

10. New Generic Socket Address Structure
struct sockaddr_storage {
uint8_t ss_len; /* length of this struct (implementation dependent) */
sa_family_t ss_family; /* address family: AF_xxx value */
….. };

12. Value-Result Arguments
Arguments used for both value passing and result returning purpose.
Process to Kernel:
bind(),connect(),sendto()
Example:
struct sockaddr_in serv; /* fill in serv{} */
connect (sockfd, (sockaddr *) &serv, sizeof(serv) );
Kernel to Process
accept(), recvfrom(), getsockname(), and getpeername()
struct sockaddr_un cli; /* Unix domain */
socklen_t len;
len = sizeof(cli); /* len is a value */
getpeername(unixfd, (sockaddr *) &cli, &len); /* len may have changed */

14. Byte Ordering Functions

15. #include <netinet/in.h>
uint16_t htons(uint16_t host16bitvalue) ;
uint32_t htonl(uint32_t host32bitvalue) uint16_t ntohs(uint16_t net16bitvalue) ;
uint32_t ntohl(uint32_t net32bitvalue) ;

16. Byte Manipulation Functions

17. Address Conversion
Functions to convert 32 bit IPv4 network address to Ascii string
0x => “ ”
inet_aton(), net_ntoa()

18. Address Conversion
Functions to convert 32 bit IPv4/IPv6 network address to Ascii string
inet_pton(), inet_ntop()

19. End