inet(7tcp)

inet -- Internet protocol family

Synopsis

#include  <sys/types.h>

#include  <netinet/in.h>

#include  <netinet/in6.h>

Description

The Internet protocol family is a set of protocols using the Internet Protocols (IPv4 and IPv6) network layer and the Internet address formats for IPv4 and IPv6. The Internet family provides protocol support for the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW interface provides access to the IP protocols.

IPv4 addressing

IPv4 Internet addresses are four-byte quantities, stored in network standard format. The include file <netinet/in.h> defines this address.

Sockets bound to the IPv4 Internet protocol family use the following addressing structure:

   struct sockaddr_in {
           sa_len_t        sin_len;
           sa_family_t     sin_family;  /* AF_INET */
           in_port_t       sin_port;
           struct in_addr  sin_addr;
           unsigned char   sin_zero[8];
   };

When using sockets, the sin_port and sin_addr fields are specified in network order.

Sockets may be created with the local address INADDR_ANY to affect ``wildcard'' matching on incoming messages. The address in a connect(3sock) or sendto (see send(3sock)) call may be given as INADDR_ANY to mean this host. The distinguished address INADDR_BROADCAST is allowed as a shorthand for the broadcast address on the primary network if the first network configured supports broadcast.

When using the Transport Layer Interface (TLI), transport providers such as tcp(7tcp) support addresses whose length varies from eight to sixteen bytes. The 8-byte form is the same as a sockaddr_in without the sin_zero field. The 16-byte form is identical to sockaddr_in.

IPv6 addressing

IPv6 Internet addresses are eight 16-bit quantities, stored in network standard format. The include file <netinet/in6.h> defines this address.

Sockets bound to the IPv6 Internet protocol family use the following addressing structure:

   struct sockaddr_in6 {
           sa_len_t        sin6_len;
           sa_family_t     sin6_family;  /* AF_INET6 */
           u_int16m_t      sin6_port;
           u_int32m_t      sin6_flowinfo;
           struct in6_addr sin6_addr;
   };

When using sockets, the sin6_port, sin6_flowinfo and sin6_addr fields are specified in network order.

NOTE: The sin6_len field need not be set before passing a socket address using bind(3sock), connect(3sock), sendto(3sock), or sendmsg(3sock).

Sockets may be created with the local address in6addr_any to affect ``wildcard'' matching on incoming messages. The address in a connect(3sock) or sendto (see send(3sock)) call may be given as in6addr_any to mean this host.

NOTE: The IN6ADDR_ constants and in6addr_ externals are defined in network byte order, unlike the INADDR_ constants which are defined in host byte order.

Protocols

The Internet protocol family is comprised of the Internet Protocol (IP), Internet Control Message Protocol (ICMP), Internet Group Management Protocol (IGMP) - IPv4 only, Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). TCP is used to support the SOCK_STREAM abstraction; UDP is used to support the SOCK_DGRAM abstraction. A raw interface to IP is available by creating an Internet socket of type SOCK_RAW. The ICMP and IGMP message protocols are accessible from a raw socket.

IPv4 network masks

The 32-bit Internet address contains both network and host parts. It is frequency-encoded; the most-significant bit is clear in Class A addresses, in which the high-order 8 bits are the network number. Class B addresses use the high-order 16 bits as the network field, and Class C addresses have a 24-bit network part. Sites with a cluster of local networks and a connection to the Internet may chose to use a single network number for the cluster; this is done by using subnet addressing. The local (host) portion of the address is further subdivided into subnet and host parts. Within a subnet, each subnet appears to be an individual network; externally, the entire cluster appears to be a single, uniform network requiring only a single routing entry. Subnet addressing is enabled and examined using the SIOCSIFNETMASK and SIOCGIFNETMASK ioctl(2) commands on a datagram socket in the Internet ``communications domain'' (see the description of the ``Interface ioctls'' on the if(7tcp) manual page).

References

icmp(7tcp), if(7tcp), igmp(7tcp), ioctl(2), ip(7tcp), ipv6(7tcp), socket(3sock), tcp(7tcp), udp(7tcp)

Notices

The Internet protocol support is subject to change as the Internet protocols develop. Users should not depend on details of the current implementation, but rather the services exported.

In UnixWare 7, the sockaddr structure has been modified to support variable length sockets. The net result of this modification is that the family member is now 8 bits and a new 8-bit member, len, has been inserted before it.