c4d9468ea0
Avoid using parenthesis enclosure macros (.Pq and .Po/.Pc) with plain text. Not only this slows down the mdoc(7) processing significantly, but it also has an undesired (in this case) effect of disabling hyphenation within the entire enclosed block.
600 lines
15 KiB
Groff
600 lines
15 KiB
Groff
.\" $FreeBSD$
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.Dd June 27, 2000
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.Dt NATD 8
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.Os
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.Sh NAME
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.Nm natd
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.Nd Network Address Translation daemon
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.Sh SYNOPSIS
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.Nm
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.Bk -words
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.Op Fl unregistered_only | u
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.Op Fl log | l
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.Op Fl proxy_only
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.Op Fl reverse
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.Op Fl deny_incoming | d
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.Op Fl use_sockets | s
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.Op Fl same_ports | m
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.Op Fl verbose | v
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.Op Fl dynamic
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.Op Fl in_port | i Ar port
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.Op Fl out_port | o Ar port
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.Op Fl port | p Ar port
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.Op Fl alias_address | a Ar address
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.Op Fl target_address | t Ar address
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.Op Fl interface | n Ar interface
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.Op Fl proxy_rule Ar proxyspec
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.Op Fl redirect_port Ar linkspec
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.Op Fl redirect_proto Ar linkspec
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.Op Fl redirect_address Ar linkspec
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.Op Fl config | f Ar configfile
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.Op Fl log_denied
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.Op Fl log_facility Ar facility_name
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.Op Fl punch_fw Ar firewall_range
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.Ek
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.Sh DESCRIPTION
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This program provides a Network Address Translation facility for use
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with
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.Xr divert 4
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sockets under
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.Fx .
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It is intended for use with NICs - if you want to do NAT on a PPP link,
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use the
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.Fl nat
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switch to
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.Xr ppp 8 .
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.Pp
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The
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.Nm
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normally runs in the background as a daemon.
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It is passed raw IP packets as they travel into and out of the machine,
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and will possibly change these before re-injecting them back into the
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IP packet stream.
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.Pp
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It changes all packets destined for another host so that their source
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IP number is that of the current machine.
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For each packet changed in this manner, an internal table entry is
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created to record this fact.
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The source port number is also changed to indicate the table entry
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applying to the packet.
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Packets that are received with a target IP of the current host are
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checked against this internal table.
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If an entry is found, it is used to determine the correct target IP
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number and port to place in the packet.
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.Pp
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The following command line options are available:
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.Bl -tag -width Fl
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.It Fl log | l
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Log various aliasing statistics and information to the file
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.Pa /var/log/alias.log .
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This file is truncated each time
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.Nm
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is started.
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.It Fl deny_incoming | d
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Do not pass incoming packets that have no
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entry in the internal translation table.
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.Pp
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If this option is not used, then such a packet will be altered
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using the rules in
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.Fl target_address
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below, and the entry will be made in the internal translation table.
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.It Fl log_denied
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Log denied incoming packets via
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.Xr syslog 3
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(see also
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.Fl log_facility ) .
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.It Fl log_facility Ar facility_name
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Use specified log facility when logging information via
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.Xr syslog 3 .
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Argument
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.Ar facility_name
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is one of the keywords specified in
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.Xr syslog.conf 5 .
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.It Fl use_sockets | s
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Allocate a
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.Xr socket 2
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in order to establish an FTP data or IRC DCC send connection.
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This option uses more system resources, but guarantees successful
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connections when port numbers conflict.
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.It Fl same_ports | m
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Try to keep the same port number when altering outgoing packets.
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With this option, protocols such as RPC will have a better chance
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of working.
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If it is not possible to maintain the port number, it will be silently
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changed as per normal.
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.It Fl verbose | v
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Do not call
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.Xr daemon 3
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on startup.
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Instead, stay attached to the controlling terminal and display all packet
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alterations to the standard output.
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This option should only be used for debugging purposes.
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.It Fl unregistered_only | u
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Only alter outgoing packets with an
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.Em unregistered
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source address.
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According to RFC 1918, unregistered source addresses are 10.0.0.0/8,
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172.16.0.0/12 and 192.168.0.0/16.
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.It Fl redirect_port Ar proto Xo
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.Ar targetIP Ns : Ns Xo
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.Ar targetPORT Ns Op - Ns Ar targetPORT Xc
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.Op Ar aliasIP Ns : Ns Xo
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.Ar aliasPORT Ns Op - Ns Ar aliasPORT Xc
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.Oo Ar remoteIP Ns Oo : Ns
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.Ar remotePORT Ns Op - Ns Ar remotePORT
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.Oc Oc
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.Xc
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Redirect incoming connections arriving to given port(s) to another host
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and port(s).
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Argument
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.Ar proto
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is either
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.Ar tcp
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or
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.Ar udp ,
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.Ar targetIP
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is the desired target IP number,
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.Ar targetPORT
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is the desired target port number or range,
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.Ar aliasPORT
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is the requested port number or range, and
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.Ar aliasIP
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is the aliasing address.
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Arguments
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.Ar remoteIP
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and
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.Ar remotePORT
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can be used to specify the connection more accurately if necessary.
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The
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.Ar targetPORT
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range and
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.Ar aliasPORT
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range need not be the same numerically, but must have the same size.
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If
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.Ar remotePORT
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is not specified, it is assumed to be all ports.
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If
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.Ar remotePORT
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is specified, it must match the size of
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.Ar targetPORT ,
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or be 0 (all ports).
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For example, the argument
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.Pp
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.Dl Ar tcp inside1:telnet 6666
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.Pp
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means that incoming TCP packets destined for port 6666 on this machine
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will be sent to the telnet port on the inside1 machine.
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.Pp
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.Dl Ar tcp inside2:2300-2399 3300-3399
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.Pp
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will redirect incoming connections on ports 3300-3399 to host
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inside2, ports 2300-2399.
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The mapping is 1:1 meaning port 3300 maps to 2300, 3301 maps to 2301, etc.
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.It Fl redirect_proto Ar proto localIP Oo
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.Ar publicIP Op Ar remoteIP
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.Oc
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Redirect incoming IP packets of protocol
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.Ar proto
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(see
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.Xr protocols 5 )
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destined for
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.Ar publicIP
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address to a
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.Ar localIP
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address and vice versa.
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.Pp
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If
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.Ar publicIP
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is not specified, then the default aliasing address is used.
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If
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.Ar remoteIP
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is specified, then only packets coming from/to
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.Ar remoteIP
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will match the rule.
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.It Fl redirect_address Ar localIP publicIP
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Redirect traffic for public IP address to a machine on the local
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network.
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This function is known as
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.Em static NAT .
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Normally static NAT is useful if your ISP has allocated a small block
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of IP addresses to you, but it can even be used in the case of single
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address:
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.Pp
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.Dl Ar redirect_address 10.0.0.8 0.0.0.0
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.Pp
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The above command would redirect all incoming traffic
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to machine 10.0.0.8.
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.Pp
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If several address aliases specify the same public address
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as follows
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.Bd -literal -offset indent
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.Ar redirect_address 192.168.0.2 public_addr
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.Ar redirect_address 192.168.0.3 public_addr
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.Ar redirect_address 192.168.0.4 public_addr
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.Ed
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.Pp
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the incoming traffic will be directed to the last
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translated local address (192.168.0.4), but outgoing
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traffic from the first two addresses will still be aliased
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to appear from the specified
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.Ar public_addr .
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.It Fl redirect_port Ar proto Xo
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.Ar targetIP Ns : Ns Xo
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.Ar targetPORT Ns Oo , Ns
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.Ar targetIP Ns : Ns Xo
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.Ar targetPORT Ns Oo , Ns
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.Ar ...\&
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.Oc Oc
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.Xc
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.Xc
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.Op Ar aliasIP Ns : Ns Xo
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.Ar aliasPORT
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.Xc
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.Oo Ar remoteIP Ns
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.Op : Ns Ar remotePORT
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.Oc
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.Xc
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.It Fl redirect_address Xo
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.Ar localIP Ns Oo , Ns
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.Ar localIP Ns Oo , Ns
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.Ar ...\&
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.Oc Oc
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.Ar publicIP
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.Xc
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These forms of
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.Fl redirect_port
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and
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.Fl redirect_address
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are used to transparently offload network load on a single server and
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distribute the load across a pool of servers.
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This function is known as
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.Em LSNAT
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(RFC 2391).
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For example, the argument
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.Pp
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.Dl Ar tcp www1:http,www2:http,www3:http www:http
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.Pp
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means that incoming HTTP requests for host www will be transparently
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redirected to one of the www1, www2 or www3, where a host is selected
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simply on a round-robin basis, without regard to load on the net.
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.It Fl dynamic
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If the
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.Fl n
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or
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.Fl interface
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option is used,
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.Nm
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will monitor the routing socket for alterations to the
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.Ar interface
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passed.
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If the interface's IP number is changed,
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.Nm
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will dynamically alter its concept of the alias address.
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.It Fl in_port | i Ar port
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Read from and write to
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.Xr divert 4
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port
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.Ar port ,
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treating all packets as
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.Dq incoming .
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.It Fl out_port | o Ar port
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Read from and write to
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.Xr divert 4
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port
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.Ar port ,
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treating all packets as
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.Dq outgoing .
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.It Fl port | p Ar port
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Read from and write to
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.Xr divert 4
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port
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.Ar port ,
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distinguishing packets as
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.Dq incoming
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or
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.Dq outgoing
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using the rules specified in
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.Xr divert 4 .
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If
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.Ar port
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is not numeric, it is searched for in the
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.Xr services 5
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database.
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If this option is not specified, the divert port named
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.Ar natd
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will be used as a default.
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.It Fl alias_address | a Ar address
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Use
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.Ar address
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as the aliasing address.
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If this option is not specified, the
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.Fl interface
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option must be used.
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The specified address is usually the address assigned to the
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.Dq public
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network interface.
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.Pp
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All data passing
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.Em out
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will be rewritten with a source address equal to
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.Ar address .
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All data coming
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.Em in
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will be checked to see if it matches any already-aliased outgoing
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connection.
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If it does, the packet is altered accordingly.
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If not, all
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.Fl redirect_port ,
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.Fl redirect_proto
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and
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.Fl redirect_address
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assignments are checked and actioned.
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If no other action can be made and if
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.Fl deny_incoming
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is not specified, the packet is delivered to the local machine
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using the rules specified in
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.Fl target_address
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option below.
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.It Fl t | target_address Ar address
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Set the target address.
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When an incoming packet not associated with any pre-existing link
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arrives at the host machine, it will be sent to the specified
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.Ar address .
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.Pp
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The target address may be set to
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.Ar 255.255.255.255 ,
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in which case all new incoming packets go to the alias address set by
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.Fl alias_address
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or
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.Fl interface .
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.Pp
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If this option is not used, or called with the argument
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.Ar 0.0.0.0 ,
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then all new incoming packets go to the address specified in
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the packet.
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This allows external machines to talk directly to internal machines if
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they can route packets to the machine in question.
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.It Fl interface | n Ar interface
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Use
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.Ar interface
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to determine the aliasing address.
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If there is a possibility that the IP number associated with
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.Ar interface
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may change, the
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.Fl dynamic
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option should also be used.
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If this option is not specified, the
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.Fl alias_address
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option must be used.
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.Pp
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The specified
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.Ar interface
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is usually the
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.Dq public
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(or
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.Dq external )
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network interface.
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.It Fl config | f Ar file
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Read configuration from
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.Ar file .
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A
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.Ar file
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should contain a list of options, one per line, in the same form
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as the long form of the above command line options.
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For example, the line
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.Pp
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.Dl alias_address 158.152.17.1
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.Pp
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would specify an alias address of 158.152.17.1.
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Options that do not take an argument are specified with an argument of
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.Ar yes
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or
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.Ar no
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in the configuration file.
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For example, the line
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.Pp
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.Dl log yes
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.Pp
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is synonymous with
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.Fl log .
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.Pp
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Trailing spaces and empty lines are ignored.
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A
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.Ql \&#
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sign will mark the rest of the line as a comment.
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.It Fl reverse
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This option makes
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.Nm
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reverse the way it handles
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.Dq incoming
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and
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.Dq outgoing
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packets, allowing it to operate on the
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.Dq internal
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network interface rather than the
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.Dq external
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one.
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.Pp
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This can be useful in some transparent proxying situations
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when outgoing traffic is redirected to the local machine
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and
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.Nm
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is running on the internal interface (it usually runs on the
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external interface).
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.It Fl proxy_only
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Force
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.Nm
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to perform transparent proxying only.
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Normal address translation is not performed.
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.It Fl proxy_rule Xo
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.Op Ar type encode_ip_hdr | encode_tcp_stream
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.Ar port xxxx
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.Ar server a.b.c.d:yyyy
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.Xc
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Enable transparent proxying.
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Outgoing TCP packets with the given port going through this
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host to any other host are redirected to the given server and port.
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Optionally, the original target address can be encoded into the packet.
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Use
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.Ar encode_ip_hdr
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to put this information into the IP option field or
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.Ar encode_tcp_stream
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to inject the data into the beginning of the TCP stream.
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.It Fl punch_fw Xo
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.Ar basenumber Ns : Ns Ar count
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.Xc
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This option directs
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.Nm
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to
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.Dq punch holes
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in an
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.Xr ipfirewall 4
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based firewall for FTP/IRC DCC connections.
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This is done dynamically by installing temporary firewall rules which
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allow a particular connection (and only that connection) to go through
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the firewall.
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The rules are removed once the corresponding connection terminates.
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.Pp
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A maximum of
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.Ar count
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rules starting from the rule number
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.Ar basenumber
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will be used for punching firewall holes.
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The range will be cleared for all rules on startup.
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.El
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.Sh RUNNING NATD
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The following steps are necessary before attempting to run
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.Nm :
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.Bl -enum
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.It
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Build a custom kernel with the following options:
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.Bd -literal -offset indent
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options IPFIREWALL
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options IPDIVERT
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.Ed
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.Pp
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Refer to the handbook for detailed instructions on building a custom
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kernel.
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.It
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Ensure that your machine is acting as a gateway.
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This can be done by specifying the line
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.Pp
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.Dl gateway_enable=YES
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.Pp
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in the
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.Pa /etc/rc.conf
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file or using the command
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.Pp
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.Dl sysctl -w net.inet.ip.forwarding=1
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.Pp
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.It
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If you use the
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.Fl interface
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option, make sure that your interface is already configured.
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If, for example, you wish to specify
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.Ql tun0
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as your
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.Ar interface ,
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and you are using
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.Xr ppp 8
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on that interface, you must make sure that you start
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.Nm ppp
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prior to starting
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.Nm .
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.El
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.Pp
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Running
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.Nm
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is fairly straight forward.
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The line
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.Pp
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.Dl natd -interface ed0
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.Pp
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should suffice in most cases (substituting the correct interface name).
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Please check
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.Xr rc.conf 5
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on how to configure it to be started automatically during boot.
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Once
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.Nm
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is running, you must ensure that traffic is diverted to
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.Nm :
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.Bl -enum
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.It
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You will need to adjust the
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.Pa /etc/rc.firewall
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script to taste.
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If you are not interested in having a firewall, the
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following lines will do:
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.Bd -literal -offset indent
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/sbin/ipfw -f flush
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/sbin/ipfw add divert natd all from any to any via ed0
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/sbin/ipfw add pass all from any to any
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.Ed
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.Pp
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The second line depends on your interface (change
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.Ql ed0
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as appropriate).
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.Pp
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You should be aware of the fact that, with these firewall settings,
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everyone on your local network can fake his source-address using your
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host as gateway.
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If there are other hosts on your local network, you are strongly
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encouraged to create firewall rules that only allow traffic to and
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from trusted hosts.
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.Pp
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If you specify real firewall rules, it is best to specify line 2 at
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the start of the script so that
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.Nm
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sees all packets before they are dropped by the firewall.
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.Pp
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After translation by
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.Nm ,
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packets re-enter the firewall at the rule number following the rule number
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that caused the diversion (not the next rule if there are several at the
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same number).
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.It
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Enable your firewall by setting
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.Pp
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.Dl firewall_enable=YES
|
|
.Pp
|
|
in
|
|
.Pa /etc/rc.conf .
|
|
This tells the system startup scripts to run the
|
|
.Pa /etc/rc.firewall
|
|
script.
|
|
If you do not wish to reboot now, just run this by hand from the console.
|
|
NEVER run this from a remote session unless you put it into the background.
|
|
If you do, you will lock yourself out after the flush takes place, and
|
|
execution of
|
|
.Pa /etc/rc.firewall
|
|
will stop at this point - blocking all accesses permanently.
|
|
Running the script in the background should be enough to prevent this
|
|
disaster.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr divert 4 ,
|
|
.Xr protocols 5 ,
|
|
.Xr rc.conf 5 ,
|
|
.Xr services 5 ,
|
|
.Xr syslog.conf 5 ,
|
|
.Xr ipfw 8 ,
|
|
.Xr ppp 8
|
|
.Sh AUTHORS
|
|
This program is the result of the efforts of many people at different
|
|
times:
|
|
.Pp
|
|
.An Archie Cobbs Aq archie@whistle.com
|
|
(divert sockets)
|
|
.An Charles Mott Aq cmott@scientech.com
|
|
(packet aliasing)
|
|
.An Eivind Eklund Aq perhaps@yes.no
|
|
(IRC support & misc additions)
|
|
.An Ari Suutari Aq suutari@iki.fi
|
|
(natd)
|
|
.An Dru Nelson Aq dnelson@redwoodsoft.com
|
|
(early PPTP support)
|
|
.An Brian Somers Aq brian@awfulhak.org
|
|
(glue)
|
|
.An Ruslan Ermilov Aq ru@FreeBSD.org
|
|
(natd, packet aliasing, glue)
|