564 lines
14 KiB
Groff
564 lines
14 KiB
Groff
.\" $FreeBSD$
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.Dd June 27, 2000
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.Dt NATD 8
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.Os FreeBSD
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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 natd
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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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.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 packets destined for the current IP number that have no
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entry 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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.Po
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see also
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.Fl log_facility
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.Pc .
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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 controling 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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.Po see Xr protocols 5
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.Pc
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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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.Ar port ,
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treating all packets as packets coming into the machine.
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.It Fl out_port | o Ar port
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Read from and write to
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.Ar port ,
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treating all packets as packets going out of the machine.
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.It Fl port | p Ar port
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Read from and write to
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.Ar port ,
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distinguishing packets as incoming our outgoing using the rules
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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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.Em 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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public 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 unaltered to the local
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machine and port as specified in the packet, but see the
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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 public 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 option 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 incoming and outgoing packets,
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allowing it to operate on the internal interface rather than
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the external 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 natd :
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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 tun0 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 natd .
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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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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 natd :
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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 ed0 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 natd ,
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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
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.Pp
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in
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.Pa /etc/rc.conf .
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This tells the system startup scripts to run the
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.Pa /etc/rc.firewall
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script.
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If you do not wish to reboot now, just run this by hand from the console.
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NEVER run this from a remote session unless you put it into the background.
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If you do, you will lock yourself out after the flush takes place, and
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execution of
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.Pa /etc/rc.firewall
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will stop at this point - blocking all accesses permanently.
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Running the script in the background should be enough to prevent this
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disaster.
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.El
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.Sh SEE ALSO
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.Xr divert 4 ,
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.Xr protocols 5 ,
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.Xr rc.conf 5 ,
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.Xr services 5 ,
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.Xr syslog.conf 5 ,
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.Xr ipfw 8 ,
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.Xr ppp 8 .
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.Sh AUTHORS
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This program is the result of the efforts of many people at different
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times:
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.Pp
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.An Archie Cobbs Aq archie@whistle.com
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(divert sockets)
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.An Charles Mott Aq cmott@scientech.com
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(packet aliasing)
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.An Eivind Eklund Aq perhaps@yes.no
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(IRC support & misc additions)
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.An Ari Suutari Aq suutari@iki.fi
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(natd)
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.An Dru Nelson Aq dnelson@redwoodsoft.com
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(early PPTP support)
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.An Brian Somers Aq brian@awfulhak.org
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(glue)
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