303 lines
8.9 KiB
Groff
303 lines
8.9 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. 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 August 14, 2018
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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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and
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.Tn i386
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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
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.Nm
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address on an interface consist of the address itself, the
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netmask, either broadcast address in case of a broadcast
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interface or peers address in case of point-to-point interface.
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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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.Pp
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.Bl -tag -width ".Dv SIOCGIFBRDADDR" -offset indent -compact
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.It Dv SIOCAIFADDR
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Add address to an interface.
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The command requires
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.Ft struct in_aliasreq
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as argument.
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.It Dv SIOCDIFADDR
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Delete address from an interface.
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The command requires
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.Ft struct ifreq
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as argument.
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.It Dv SIOCGIFADDR
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.It Dv SIOCGIFBRDADDR
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.It Dv SIOCGIFDSTADDR
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.It Dv SIOCGIFNETMASK
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Return address information from interface.
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The returned value is in
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.Ft struct ifreq .
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This way of address information retrieval is obsoleted, a
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preferred way is to use
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.Xr getifaddrs 3
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API.
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.El
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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_ACCEPTSOURCEROUTE
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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_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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.Tn IP
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packets for which a better, and for the sender directly reachable, route
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and next hop is known.
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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 Va ip.process_options
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Integer: control IP options processing.
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By setting this variable to 0, all IP options in the incoming packets
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will be ignored, and the packets will be passed unmodified.
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By setting to 1, IP options in the incoming packets will be processed
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accordingly.
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By setting to 2, an
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.Tn ICMP
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.Dq "prohibited by filter"
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message will be sent back in response to incoming packets with IP options.
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Default is 1.
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This
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.Xr sysctl 8
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variable affects packets destined for a local host as well as packets
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forwarded to some other host.
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.It Va ip.rfc6864
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Boolean: control IP IDs generation behaviour.
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True value enables RFC6864 support, which specifies that IP ID field of
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.Em atomic
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datagrams can be set to any value.
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The
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.Fx implementation sets it to zero.
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Enabled by default.
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.It Va ip.random_id
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Boolean: control IP IDs generation behaviour.
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Setting this
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.Xr sysctl 8
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to 1 causes the ID field in
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.Em non-atomic
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IP datagrams (or all IP datagrams, if
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.Va ip.rfc6864
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is disabled) to be randomized instead of incremented by 1 with each packet
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generated.
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This closes a minor information leak which allows remote observers to
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determine the rate of packet generation on the machine by watching the
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counter.
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At the same time, on high-speed links, it can decrease the ID reuse
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cycle greatly.
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Default is 0 (sequential IP IDs).
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IPv6 flow IDs and fragment IDs are always random.
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.It Va ip.maxfrags
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Integer: maximum number of fragments the host will accept and simultaneously
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hold across all reassembly queues in all VNETs.
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If set to 0, reassembly is disabled.
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If set to -1, this limit is not applied.
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This limit is recalculated when the number of mbuf clusters is changed.
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This is a global limit.
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.It Va ip.maxfragpackets
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Integer: maximum number of fragmented packets the host will accept and
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simultaneously hold in the reassembly queue for a particular VNET.
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0 means that the host will not accept any fragmented packets for that VNET.
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\-1 means that the host will not apply this limit for that VNET.
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This limit is recalculated when the number of mbuf clusters is changed.
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This is a per-VNET limit.
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.It Va ip.maxfragbucketsize
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Integer: maximum number of reassembly queues per bucket.
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Fragmented packets are hashed to buckets.
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Each bucket has a list of reassembly queues.
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The system must compare the incoming packets to the existing reassembly queues
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in the bucket to find a matching reassembly queue.
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To preserve system resources, the system limits the number of reassembly
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queues allowed in each bucket.
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This limit is recalculated when the number of mbuf clusters is changed or
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when the value of
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.Va ip.maxfragpackets
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changes.
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This is a per-VNET limit.
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.It Va ip.maxfragsperpacket
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Integer: maximum number of fragments the host will accept and hold
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in the reassembly queue for a packet.
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0 means that the host will not accept any fragmented packets for the VNET.
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This is a per-VNET limit.
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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 getifaddrs 3 ,
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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 route 4 ,
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.Xr tcp 4 ,
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.Xr udp 4 ,
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.Xr pfil 9
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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 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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.Sh CAVEATS
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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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