INET(4F) INET(4F) NAME inet - Internet protocol family SYNOPSIS #include #include DESCRIPTION The Internet protocol family is a collection of protocols layered atop the _I_n_t_e_r_n_e_t _P_r_o_t_o_c_o_l (IP) transport layer, and utilizing the Internet address format. The Internet family provides protocol support for the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW inter‐ face provides access to the IP protocol. ADDRESSING Internet addresses are four byte quantities, stored in network standard format (on the VAX these are word and byte reversed). The include file <_n_e_t_i_n_e_t_/_i_n_._h> defines this address as a discriminated union. Sockets bound to the Internet protocol family utilize the following addressing structure, struct sockaddr_in { short sin_family; u_short sin_port; struct in_addr sin_addr; char sin_zero[8]; }; Sockets may be created with the local address INADDR_ANY to effect “wildcard” matching on incoming messages. The address in a _c_o_n_n_e_c_t(2) or _s_e_n_d_t_o(2) 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. PROTOCOLS The Internet protocol family is comprised of the IP transport protocol, Internet Control Message Protocol (ICMP), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). TCP is used to support the SOCK_STREAM abstraction while UDP is used to support the SOCK_DGRAM abstraction. A raw interface to IP is available by creating an Inter‐ net socket of type SOCK_RAW. The ICMP message protocol is accessible from a raw socket. 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 DARPA 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 subdi‐ vided 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 by the following _i_o_c_t_l(2) commands on a datagram socket in the Internet domain; they have the same form as the SIOCIFADDR command (see _i_n_t_r_o(4N)). SIOCSIFNETMASK Set interface network mask. The network mask defines the network part of the address; if it contains more of the address than the address type would indicate, then subnets are in use. SIOCGIFNETMASK Get interface network mask. SEE ALSO ioctl(2), socket(2), intro(4N), tcp(4P), udp(4P), ip(4P), icmp(4P) An Introductory 4.3BSD Interprocess Communication Tutorial (PS1:7). An Advanced 4.3BSD Interprocess Communication Tutorial (PS1:8). CAVEAT The Internet protocol support is subject to change as the Internet pro‐ tocols develop. Users should not depend on details of the current implementation, but rather the services exported. 4.2 Berkeley Distribution June 1, 1986 INET(4F)