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IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 .\" $FreeBSD: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $ .\" .Dd March 22, 2015 .Dt INET 4 .Os .Sh NAME .Nm inet .Nd Internet protocol family .Sh SYNOPSIS .In sys/types.h .In netinet/in.h .Sh DESCRIPTION The Internet protocol family is a collection of protocols layered atop the .Em Internet Protocol .Pq Tn IP transport layer, and utilizing the Internet address format. The Internet family provides protocol support for the .Dv SOCK_STREAM , SOCK_DGRAM , and .Dv SOCK_RAW socket types; the .Dv SOCK_RAW interface provides access to the .Tn IP protocol. .Sh ADDRESSING Internet addresses are four byte quantities, stored in network standard format (on the .Tn VAX these are word and byte reversed). The include file .In netinet/in.h defines this address as a discriminated union. .Pp Sockets bound to the Internet protocol family utilize the following addressing structure, .Bd -literal -offset indent struct sockaddr_in { u_char sin_len; sa_family_t sin_family; u_short sin_port; struct in_addr sin_addr; char sin_zero[8]; }; .Ed .Pp Sockets may be created with the local address .Dv INADDR_ANY to affect .Dq wildcard matching on incoming messages. The address in a .Xr connect 2 or .Xr sendto 2 call may be given as .Dv INADDR_ANY to mean .Dq this host . The distinguished address .Dv INADDR_BROADCAST is allowed as a shorthand for the broadcast address on the primary network if the first network configured supports broadcast. .Sh PROTOCOLS The Internet protocol family is comprised of the .Tn IP network protocol, Internet Control Message Protocol .Pq Tn ICMP , Internet Group Management Protocol .Pq Tn IGMP , Transmission Control Protocol .Pq Tn TCP , and User Datagram Protocol .Pq Tn UDP . .Tn TCP is used to support the .Dv SOCK_STREAM abstraction while .Tn UDP is used to support the .Dv SOCK_DGRAM abstraction. A raw interface to .Tn IP is available by creating an Internet socket of type .Dv SOCK_RAW . The .Tn ICMP message protocol is accessible from a raw socket. .Pp The 32-bit Internet address contains both network and host parts. However, direct examination of addresses is discouraged. For those programs which absolutely need to break addresses into their component parts, the following .Xr ioctl 2 commands are provided for a datagram socket in the Internet domain; they have the same form as the .Dv SIOCSIFADDR and .Dv SIOCGIFADDR commands (see .Xr intro 4 ) . .Bl -tag -width ".Dv SIOCSIFNETMASK" .It Dv 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. .It Dv SIOCGIFNETMASK Get interface network mask. .El .Sh ROUTING The current implementation of Internet protocols includes some routing-table adaptations to provide enhanced caching of certain end-to-end information necessary for Transaction TCP and Path MTU Discovery. The following changes are the most significant: .Bl -enum .It All IP routes, except those with the .Dv RTF_CLONING flag and those to multicast destinations, have the .Dv RTF_PRCLONING flag forcibly enabled (they are thus said to be .Dq "protocol cloning" ) . .It When the last reference to an IP route is dropped, the route is examined to determine if it was created by cloning such a route. If this is the case, the .Dv RTF_PROTO3 flag is turned on, and the expiration timer is initialized to go off in .Va net.inet.ip.rtexpire seconds. If such a route is re-referenced, the flag and expiration timer are reset. .It A kernel timeout runs once every ten minutes, or sooner if there are soon-to-expire routes in the kernel routing table, and deletes the expired routes. .El .Pp A dynamic process is in place to modify the value of .Va net.inet.ip.rtexpire if the number of cached routes grows too large. If after an expiration run there are still more than .Va net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire value is multiplied by \(34, and any routes which have longer expiration times have those times adjusted. This process is damped somewhat by specification of a minimum rtexpire value .Va ( net.inet.ip.rtminexpire ) , and by restricting the reduction to once in a ten-minute period. .Pp If some external process deletes the original route from which a protocol-cloned route was generated, the ``child route'' is deleted. (This is actually a generic mechanism in the routing code support for protocol-requested cloning.) .Pp No attempt is made to manage routes which were not created by protocol cloning; these are assumed to be static, under the management of an external routing process, or under the management of a link layer (e.g., .Tn ARP for Ethernets). .Pp Only certain types of network activity will result in the cloning of a route using this mechanism. Specifically, those protocols (such as .Tn TCP and .Tn UDP ) which themselves cache a long-lasting reference to route for a destination will trigger the mechanism; whereas raw .Tn IP packets, whether locally-generated or forwarded, will not. .Ss MIB Variables A number of variables are implemented in the net.inet branch of the .Xr sysctl 3 MIB. In addition to the variables supported by the transport protocols (for which the respective manual pages may be consulted), the following general variables are defined: .Bl -tag -width IPCTL_FASTFORWARDING .It Dv IPCTL_FORWARDING .Pq ip.forwarding Boolean: enable/disable forwarding of IP packets. Defaults to off. .It Dv IPCTL_FASTFORWARDING .Pq ip.fastforwarding Boolean: enable/disable the use of fast IP forwarding code. Defaults to off. When fast forwarding is enabled, IP packets are forwarded directly to the appropriate network interface with a minimal validity checking, which greatly improves the throughput. On the other hand, they bypass the standard procedures, such as IP option processing and .Xr ipfirewall 4 checking. It is not guaranteed that every packet will be fast-forwarded. .It Dv IPCTL_SENDREDIRECTS .Pq ip.redirect Boolean: enable/disable sending of ICMP redirects in response to unforwardable .Tn IP packets. Defaults to on. .It Dv IPCTL_DEFTTL .Pq ip.ttl Integer: default time-to-live .Pq Dq TTL to use for outgoing .Tn IP packets. .It Dv IPCTL_SOURCEROUTE .Pq ip.sourceroute Boolean: enable/disable forwarding of source-routed IP packets (default false). .It Dv IPCTL_RTEXPIRE .Pq ip.rtexpire Integer: lifetime in seconds of protocol-cloned .Tn IP routes after the last reference drops (default one hour). This value varies dynamically as described above. .It Dv IPCTL_RTMINEXPIRE .Pq ip.rtminexpire Integer: minimum value of ip.rtexpire (default ten seconds). This value has no effect on user modifications, but restricts the dynamic adaptation described above. .It Dv IPCTL_RTMAXCACHE .Pq ip.rtmaxcache Integer: trigger level of cached, unreferenced, protocol-cloned routes which initiates dynamic adaptation (default 128). .El .Sh SEE ALSO .Xr ioctl 2 , .Xr socket 2 , .Xr sysctl 3 , .Xr icmp 4 , .Xr intro 4 , .Xr ip 4 , .Xr ipfirewall 4 , .Xr tcp 4 , .Xr udp 4 .Rs .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" .%B PS1 .%N 7 .Re .Rs .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" .%B PS1 .%N 8 .Re .Sh CAVEATS 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. .Sh HISTORY The .Nm protocol interface appeared in .Bx 4.2 . The .Dq protocol cloning code appeared in .Fx 2.1 .