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 connect.2 or sendto.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.
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 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 by the following ioctl.2 commands on a datagram socket in the Internet domain; they have the same form as the SIOCIFADDR command (see intro.4n
An Introductory 4.3BSD Interprocess Communication Tutorial (PS1:7).
An Advanced 4.3BSD Interprocess Communication Tutorial (PS1:8).
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