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inet(4)

NAME

     inet -- Internet protocol family

SYNOPSIS

     #include <sys/types.h>
     #include <netinet/in.h>

DESCRIPTION

     The Internet protocol family is a collection of protocols layered atop
     the Internet Protocol (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 little endian machines, such as the alpha, amd64, i386 and
     ia64 these are word and byte reversed).  The include file <netinet/in.h>
     defines this address as a discriminated union.

     Sockets bound to the Internet protocol family utilize the following
     addressing structure,

	   struct sockaddr_in {
		   uint8_t	   sin_len;
		   sa_family_t	   sin_family;
		   in_port_t	   sin_port;
		   struct in_addr  sin_addr;
		   char 	   sin_zero[8];
	   };

     Sockets may be created with the local address INADDR_ANY to affect
     ``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.

PROTOCOLS

     The Internet protocol family is comprised of the IP network protocol,
     Internet Control Message Protocol (ICMP), Internet Group Management Pro-
     tocol (IGMP), Transmission Control Protocol (TCP), and User Datagram Pro-
     tocol (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 Internet 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.	How-
     ever, direct examination of addresses is discouraged.  For those programs
     which absolutely need to break addresses into their component parts, the
     following ioctl(2) commands are provided for a datagram socket in the
     Internet domain; they have the same form as the SIOCIFADDR command (see
     intro(4)).

     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 sub-

     following general variables are defined:

     IPCTL_FORWARDING	   (ip.forwarding) Boolean: enable/disable forwarding
			   of IP packets.  Defaults to off.

     IPCTL_FASTFORWARDING  (ip.fastforwarding) Boolean: enable/disable the use
			   of fast IP forwarding code.	Defaults to off.  When
			   fast IP forwarding is enabled, IP packets are for-
			   warded directly to the appropriate network inter-
			   face with direct processing to completion, which
			   greatly improves the throughput.  All packets for
			   local IP addresses, non-unicast, or with IP options
			   are handled by the normal IP input processing path.
			   All features of the normal (slow) IP forwarding
			   path are supported including firewall (through
			   pfil(9) hooks) checking, except ipsec(4) tunnel
			   brokering.  The IP fastforwarding path does not
			   generate ICMP redirect or source quench messages.

     IPCTL_SENDREDIRECTS   (ip.redirect) Boolean: enable/disable sending of
			   ICMP redirects in response to IP packets for which
			   a better, and for the sender directly reachable,
			   route and next hop is known.  Defaults to on.

     IPCTL_DEFTTL	   (ip.ttl) Integer: default time-to-live (``TTL'') to
			   use for outgoing IP packets.

     IPCTL_ACCEPTSOURCEROUTE
			   (ip.accept_sourceroute) Boolean: enable/disable
			   accepting of source-routed IP packets (default
			   false).

     IPCTL_SOURCEROUTE	   (ip.sourceroute) Boolean: enable/disable forwarding
			   of source-routed IP packets (default false).

     IPCTL_RTEXPIRE	   (ip.rtexpire) Integer: lifetime in seconds of pro-
			   tocol-cloned IP routes after the last reference
			   drops (default one hour).  This value varies dynam-
			   ically as described above.

     IPCTL_RTMINEXPIRE	   (ip.rtminexpire) Integer: minimum value of ip.rtex-
			   pire (default ten seconds).	This value has no
			   effect on user modifications, but restricts the
			   dynamic adaptation described above.

     IPCTL_RTMAXCACHE	   (ip.rtmaxcache) Integer: trigger level of cached,
			   unreferenced, protocol-cloned routes which initi-
			   ates dynamic adaptation (default 128).

     ip.process_options    Integer: control IP options processing.  By setting
			   this variable to 0, all IP options in the incoming
			   packets will be ignored, and the packets will be
			   passed unmodified.  By setting to 1, IP options in
			   the incoming packets will be processed accordingly.
			   By setting to 2, an ICMP ``prohibited by filter''
			   message will be sent back in respose to incoming
			   packets with IP options.  Default is 1.  This
			   sysctl(8) variable affects packets destined for a
			   observers to determine the rate of packet genera-
			   tion on the machine by watching the counter.  In
			   the same time, on high-speed links, it can decrease
			   the ID reuse cycle greatly.	Default is 0 (sequen-
			   tial IP IDs).  IPv6 flow IDs and fragment IDs are
			   always random.

SEE ALSO

     ioctl(2), socket(2), sysctl(3), icmp(4), intro(4), ip(4), ipfirewall(4),
     route(4), tcp(4), ttcp(4), udp(4), pfil(9)

     "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7.

     "An Advanced 4.3 BSD Interprocess Communication Tutorial", PS1, 8.

CAVEAT

     The Internet protocol support is subject to change as the Internet proto-
     cols develop.  Users should not depend on details of the current imple-
     mentation, but rather the services exported.

HISTORY

     The inet protocol interface appeared in 4.2BSD.  The ``protocol cloning''
     code appeared in FreeBSD 2.1.

FreeBSD 5.4		       October 23, 2004 		   FreeBSD 5.4

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