313 lines
9.3 KiB
Groff
313 lines
9.3 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd February 14, 1995
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.Dt INET 4
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.Os
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.Sh NAME
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.Nm inet
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.Nd Internet protocol family
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.Sh SYNOPSIS
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.In sys/types.h
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.In netinet/in.h
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.Sh DESCRIPTION
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The Internet protocol family is a collection of protocols
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layered atop the
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.Em Internet Protocol
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.Pq Tn IP
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transport layer, and utilizing the Internet address format.
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The Internet family provides protocol support for the
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.Dv SOCK_STREAM , SOCK_DGRAM ,
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and
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.Dv SOCK_RAW
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socket types; the
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.Dv SOCK_RAW
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interface provides access to the
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.Tn IP
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protocol.
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.Sh ADDRESSING
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Internet addresses are four byte quantities, stored in
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network standard format (on little endian machines, such as the
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.Tn alpha ,
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.Tn amd64 ,
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.Tn i386
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and
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.Tn ia64
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these are word and byte reversed).
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The include file
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.In netinet/in.h
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defines this address
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as a discriminated union.
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.Pp
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Sockets bound to the Internet protocol family utilize
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the following addressing structure,
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.Bd -literal -offset indent
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struct sockaddr_in {
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uint8_t sin_len;
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sa_family_t sin_family;
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in_port_t sin_port;
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struct in_addr sin_addr;
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char sin_zero[8];
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};
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.Ed
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.Pp
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Sockets may be created with the local address
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.Dv INADDR_ANY
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to affect
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.Dq wildcard
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matching on incoming messages.
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The address in a
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.Xr connect 2
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or
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.Xr sendto 2
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call may be given as
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.Dv INADDR_ANY
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to mean
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.Dq this host .
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The distinguished address
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.Dv INADDR_BROADCAST
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is allowed as a shorthand for the broadcast address on the primary
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network if the first network configured supports broadcast.
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.Sh PROTOCOLS
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The Internet protocol family is comprised of
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the
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.Tn IP
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network protocol, Internet Control
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Message Protocol
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.Pq Tn ICMP ,
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Internet Group Management Protocol
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.Pq Tn IGMP ,
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Transmission Control
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Protocol
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.Pq Tn TCP ,
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and User Datagram Protocol
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.Pq Tn UDP .
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.Tn TCP
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is used to support the
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.Dv SOCK_STREAM
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abstraction while
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.Tn UDP
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is used to support the
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.Dv SOCK_DGRAM
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abstraction.
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A raw interface to
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.Tn IP
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is available
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by creating an Internet socket of type
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.Dv SOCK_RAW .
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The
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.Tn ICMP
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message protocol is accessible from a raw socket.
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.Pp
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The 32-bit Internet address contains both network and host parts.
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However, direct examination of addresses is discouraged.
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For those
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programs which absolutely need to break addresses into their component
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parts, the following
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.Xr ioctl 2
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commands are provided for a datagram socket in the Internet domain;
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they have the same form as the
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.Dv SIOCIFADDR
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command (see
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.Xr intro 4 ) .
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.Pp
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.Bl -tag -width SIOCSIFNETMASK
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.It Dv SIOCSIFNETMASK
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Set interface network mask.
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The network mask defines the network part of the address;
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if it contains more of the address than the address type would indicate,
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then subnets are in use.
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.It Dv SIOCGIFNETMASK
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Get interface network mask.
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.El
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.Sh ROUTING
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The current implementation of Internet protocols includes some routing-table
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adaptations to provide enhanced caching of certain end-to-end
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information necessary for Transaction TCP and Path MTU Discovery.
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The
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following changes are the most significant:
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.Bl -enum
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.It
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All IP routes, except those with the
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.Dv RTF_CLONING
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flag and those to multicast destinations, have the
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.Dv RTF_PRCLONING
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flag forcibly enabled (they are thus said to be
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.Dq "protocol cloning" ) .
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.It
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When the last reference to an IP route is dropped, the route is
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examined to determine if it was created by cloning such a route.
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If this is the case, the
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.Dv RTF_PROTO3
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flag is turned on, and the expiration timer is initialized to go off
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in net.inet.ip.rtexpire seconds.
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If such a route is re-referenced,
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the flag and expiration timer are reset.
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.It
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A kernel timeout runs once every ten minutes, or sooner if there are
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soon-to-expire routes in the kernel routing table, and deletes the
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expired routes.
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.El
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.Pp
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A dynamic process is in place to modify the value of
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net.inet.ip.rtexpire if the number of cached routes grows too large.
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If after an expiration run there are still more than
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net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire
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value is multiplied by 3/4, and any routes which have longer
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expiration times have those times adjusted.
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This process is damped somewhat by specification of a minimum rtexpire value
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(net.inet.ip.rtminexpire), and by restricting the reduction to once in
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a ten-minute period.
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.Pp
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If some external process deletes the original route from which a
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protocol-cloned route was generated, the
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.Dq child route
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is deleted.
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(This is actually a generic mechanism in the routing code support for
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protocol-requested cloning.)
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.Pp
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No attempt is made to manage routes which were not created by protocol
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cloning; these are assumed to be static, under the management of an
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external routing process, or under the management of a link layer
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(e.g.,
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.Tn ARP
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for Ethernets).
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.Pp
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Only certain types of network activity will result in the cloning of a
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route using this mechanism.
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Specifically, those protocols (such as
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.Tn TCP
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and
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.Tn UDP )
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which themselves cache a long-lasting reference to route for a destination
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will trigger the mechanism; whereas raw
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.Tn IP
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packets, whether locally-generated or forwarded, will not.
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.Ss MIB Variables
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A number of variables are implemented in the net.inet branch of the
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.Xr sysctl 3
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MIB.
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In addition to the variables supported by the transport protocols
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(for which the respective manual pages may be consulted),
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the following general variables are defined:
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.Bl -tag -width IPCTL_FASTFORWARDING
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.It Dv IPCTL_FORWARDING
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.Pq ip.forwarding
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Boolean: enable/disable forwarding of IP packets.
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Defaults to off.
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.It Dv IPCTL_FASTFORWARDING
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.Pq ip.fastforwarding
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Boolean: enable/disable the use of fast IP forwarding code.
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Defaults to off.
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When fast forwarding is enabled, IP packets are forwarded directly to
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the appropriate network interface with a minimal validity checking, which
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greatly improves the throughput.
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On the other hand, they bypass the
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standard procedures, such as IP option processing and
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.Xr ipfirewall 4
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checking.
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It is not guaranteed that every packet will be fast-forwarded.
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.It Dv IPCTL_SENDREDIRECTS
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.Pq ip.redirect
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Boolean: enable/disable sending of ICMP redirects in response to
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unforwardable
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.Tn IP
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packets.
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Defaults to on.
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.It Dv IPCTL_DEFTTL
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.Pq ip.ttl
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Integer: default time-to-live
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.Pq Dq TTL
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to use for outgoing
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.Tn IP
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packets.
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.It Dv IPCTL_ACCEPTSOURCEROUTE
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.Pq ip.accept_sourceroute
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Boolean: enable/disable accepting of source-routed IP packets (default false).
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.It Dv IPCTL_SOURCEROUTE
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.Pq ip.sourceroute
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Boolean: enable/disable forwarding of source-routed IP packets (default false).
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.It Dv IPCTL_RTEXPIRE
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.Pq ip.rtexpire
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Integer: lifetime in seconds of protocol-cloned
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.Tn IP
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routes after the last reference drops (default one hour).
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This value varies dynamically as described above.
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.It Dv IPCTL_RTMINEXPIRE
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.Pq ip.rtminexpire
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Integer: minimum value of ip.rtexpire (default ten seconds).
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This value has no effect on user modifications, but restricts the dynamic
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adaptation described above.
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.It Dv IPCTL_RTMAXCACHE
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.Pq ip.rtmaxcache
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Integer: trigger level of cached, unreferenced, protocol-cloned routes
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which initiates dynamic adaptation (default 128).
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.El
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr socket 2 ,
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.Xr sysctl 3 ,
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.Xr icmp 4 ,
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.Xr intro 4 ,
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.Xr ip 4 ,
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.Xr ipfirewall 4 ,
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.Xr tcp 4 ,
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.Xr ttcp 4 ,
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.Xr udp 4
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.Rs
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.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 7
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.Re
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.Rs
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.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 8
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.Re
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.Sh CAVEAT
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The Internet protocol support is subject to change as
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the Internet protocols develop.
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Users should not depend
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on details of the current implementation, but rather
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the services exported.
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.Sh HISTORY
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The
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.Nm
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protocol interface appeared in
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.Bx 4.2 .
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The
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.Dq protocol cloning
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code appeared in
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.Fx 2.1 .
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