403 lines
11 KiB
Groff
403 lines
11 KiB
Groff
.\" manual page [] for natd 1.4
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.Dd 15 April 1997
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.Os FreeBSD
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.Dt NATD 8
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.Sh NAME
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.Nm natd
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.Nd
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Network Address Translation Daemon
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.Sh SYNOPSIS
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.Nm
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.Op Fl ldsmvu
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.Op Fl permanent_link
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.Op Fl dynamic
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.Op Fl i Ar inport
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.Op Fl o Ar outport
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.Op Fl p Ar port
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.Op Fl a Ar address
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.Op Fl i Ar interface
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.Op Fl f Ar configfile
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.Nm
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.Op Fl log
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.Op Fl deny_incoming
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.Op Fl use_sockets
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.Op Fl same_ports
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.Op Fl verbose
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.Op Fl unregistered_only
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.Op Fl permanent_link
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.Op Fl dynamic
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.Op Fl inport Ar inport
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.Op Fl outport Ar outport
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.Op Fl port Ar port
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.Op Fl alias_address Ar address
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.Op Fl interface Ar interface
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.Op Fl config Ar configfile
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.Op Fl redirect_port Ar linkspec
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.Op Fl redirect_address Ar localIP publicIP
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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 FreeBSD. Most of the command line options are available
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in a single character short form or in a long form. Use of the long
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form is encouraged as it makes things clearer to the casual observer.
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.Pp
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.Nm Natd
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normally runs in the background as a daemon. It is passed raw IP packets
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as they travel into and out of the machine, and will possibly change these
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before re-injecting them back into the IP packet stream.
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.Pp
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.Nm Natd
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changes all packets destined for another host so that their source
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IP number is that of the current machine. For each packet changed
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in this manner, an internal table entry is created to record this
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fact. The source port number is also changed to indicate the
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table entry applying to the packet. Packets that are received with
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a target IP of the current host are checked against this internal
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table. If an entry is found, it is used to determine the correct
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target IP 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 natd is started.
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.It Fl deny_incoming | d
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Reject packets destined for the current IP number that have no entry
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in the internal translation table.
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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. This
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option uses more system resources, but guarantees successful connections
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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. If it is not possible to maintain the port number, it
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will be silently changed as per normal.
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.It Fl verbose | v
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Don't call
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.Xr fork 2
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or
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.Xr daemon 3
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on startup. Instead, stay attached to the controling terminal and
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display all packet alterations to the standard output. This option
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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 unregistered 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 linkspec
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Redirect incoming connections arriving to given port to another host and port.
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Linkspec is of the form
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proto targetIP:targetPORT [aliasIP:]aliasPORT [remoteIP[:remotePORT]]
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where proto is either tcp or udp, targetIP is the desired target IP
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number, targetPORT is the desired target PORT number, aliasPORT
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is the requested PORT number and aliasIP is the aliasing address.
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RemoteIP and remotePORT can be used to specify the connection
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more accurately if necessary.
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For example, the argument
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.Ar tcp inside1:telnet 6666
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means that tcp packets destined for port 6666 on this machine will
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be sent to the telnet port on the inside1 machine.
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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. This function is known as "static NAT". Normally static NAT
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is useful if your ISP has allocated a small block of IP addresses to you,
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but it can even be used in the case of single address:
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redirect_address 10.0.0.8 0.0.0.0
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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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If several address aliases specify the same public address
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as follows
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redirect_address 192.168.0.2 public_addr
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redirect_address 192.168.0.3 public_addr
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redirect_address 192.168.0.4 public_addr
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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 to the first two addresses will still be aliased
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to specified public address.
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.It Fl permanent_link Ar linkspec
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Create a permanent entry in the internal alias table. Linkspec is
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of the form
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proto targetIP:targetPORT sourceIP:sourcePORT aliasPORT
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where proto is either tcp or udp, targetIP is the desired target IP
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number, targetPORT is the desired target PORT number, sourceIP and
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sourcePORT match the incoming packet, and aliasPORT is the requested
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PORT number. Values of zero are considered as wildcards. For example,
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the argument
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.Ar tcp inside1:telnet outside1:0 6666
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means that tcp packets destined for port 6666 on this machine from the
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outside1 machine (any port) will be sent to the telnet port on the
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inside1 machine.
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New installations are encouraged to use redirect_port instead.
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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. If the interfaces 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 i | inport Ar inport
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Read from and write to
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.Ar inport ,
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treating all packets as packets coming into the machine.
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.It Fl o | outport Ar outport
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Read from and write to
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.Ar outport ,
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treating all packets as packets going out of the machine.
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.It Fl p | port 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 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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.Pa /etc/services
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database using the
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.Xr getservbyname 3
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function. If this flag is not specified, the divert port named natd will
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be used as a default. An example entry in the
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.Pa /etc/services
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database would be:
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natd 6668/divert # Network Address Translation socket
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Refer to
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.Xr services 5
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for further details.
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.It Fl a | alias_address Ar address
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Use
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.Ar address
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as the alias address. If this option is not specified, the
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.Fl n
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or
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.Fl interface
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option must be used. The specified address should be the address assigned
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to the public network interface.
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.Pp
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All data passing out through this addresses interface will be rewritten
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with a source address equal to
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.Ar address .
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All data arriving at the interface from outside will be checked to
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see if it matches any already-aliased outgoing connection. If it does,
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the packet is altered accordingly. If not, all
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.Fl redirect_port
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and
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.Fl redirect_address
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assignments are checked and actioned. If no other action can be made,
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and if
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.Fl deny_incoming
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is not specified, the packet is delivered to the local machine and port
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as specified in the packet.
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.It Fl n | interface Ar interface
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Use
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.Ar interface
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to determine the alias address. If there is a possibility that the
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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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flag should also be used. If this option is not specified, the
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.Fl a
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or
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.Fl alias_address
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flag must be used.
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.Pp
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The specified
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.Ar interface
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must be the public network interface.
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.It Fl f | config Ar configfile
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Read configuration from
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.Ar configfile .
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.Ar Configfile
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contains a list of options, one per line in the same form as the
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long form of the above command line flags. For example, the line
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alias_address 158.152.17.1
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would specify an alias address of 158.152.17.1. Options that don't
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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. For example, the line
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log yes
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is synonomous with
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.Fl log .
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Empty lines and lines beginning with '#' are ignored.
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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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Get FreeBSD version 2.2 or higher. Versions before this do not support
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.Xr divert 4
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sockets.
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.It
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Build a custom kernel with the following options:
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options IPFIREWALL
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options IPDIVERT
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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. This can be done by
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specifying the line
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gateway_enable=YES
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in
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.Pa /etc/rc.conf ,
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or using the command
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sysctl -w net.inet.ip.forwarding=1
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.It
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If you wish to use the
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.Fl n
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or
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.Fl interface
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flags, make sure that your interface is already configured. If, for
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example, you wish to specify tun0 as your
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.Ar interface ,
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and you're 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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.It
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Create an entry in
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.Pa /etc/services :
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natd 6668/divert # Network Address Translation socket
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This gives a default for the
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.Fl p
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or
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.Fl port
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flag.
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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. The line
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natd -interface ed0
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should suffice in most cases (substituting the correct interface name). Once
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.Nm
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is running, you must ensure that traffic is diverted to 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. If you're not interested in having a firewall, the
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following lines will do:
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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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The second line depends on your interface (change ed0 as appropriate)
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and assumes that you've updated
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.Pa /etc/services
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with the natd entry as above. If you specify real firewall rules, it's
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best to specify line 2 at 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. The firewall
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rules will be run again on each packet after translation by
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.Nm natd ,
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minus any divert rules.
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.It
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Enable your firewall by setting
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firewall_enable=YES
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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. If you don't wish to reboot now, just run this by hand from the
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console. NEVER run this from a virtual session unless you put it into
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the background. If you do, you'll lock yourself out after the flush
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takes place, and execution of
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.Pa /etc/rc.firewall
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will stop at this point - blocking all accesses permanently. Running
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the script in the background should be enough to prevent this disaster.
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.El
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.Sh SEE ALSO
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.Xr getservbyname 2 ,
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.Xr socket 2 ,
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.Xr divert 4 ,
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.Xr services 5 ,
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.Xr ipfw 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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Divert sockets: Archie Cobbs <archie@whistle.com>
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Packet aliasing: Charles Mott <cmott@srv.net>
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IRC support & misc additions: Eivind Eklund <perhaps@yes.no>
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Natd: Ari Suutari <suutari@iki.fi>
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Glue: Brian Somers <brian@awfulhak.org>
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