1 .\" manual page [] for natd 1.4
2 .\" $Id: natd.8,v 1.4 2002/05/10 00:51:01 mscopp Exp $
8 .Nd Network Address Translation daemon
12 .Op Fl unregistered_only | u
16 .Op Fl deny_incoming | d
17 .Op Fl use_sockets | s
21 .Op Fl in_port | i Ar port
22 .Op Fl out_port | o Ar port
23 .Op Fl port | p Ar port
24 .Op Fl alias_address | a Ar address
25 .Op Fl target_address | t Ar address
26 .Op Fl interface | n Ar interface
27 .Op Fl proxy_rule Ar proxyspec
28 .Op Fl redirect_port Ar linkspec
29 .Op Fl redirect_proto Ar linkspec
30 .Op Fl redirect_address Ar linkspec
31 .Op Fl config | f Ar configfile
33 .Op Fl log_facility Ar facility_name
34 .Op Fl punch_fw Ar firewall_range
37 This program provides a Network Address Translation facility for use
42 It is intended for use with NICs - if you want to do NAT on a PPP link,
50 normally runs in the background as a daemon.
51 It is passed raw IP packets as they travel into and out of the machine,
52 and will possibly change these before re-injecting them back into the
55 It changes all packets destined for another host so that their source
56 IP number is that of the current machine.
57 For each packet changed in this manner, an internal table entry is
58 created to record this fact.
59 The source port number is also changed to indicate the table entry
60 applying to the packet.
61 Packets that are received with a target IP of the current host are
62 checked against this internal table.
63 If an entry is found, it is used to determine the correct target IP
64 number and port to place in the packet.
66 The following command line options are available:
69 Log various aliasing statistics and information to the file
70 .Pa /var/log/alias.log .
71 This file is truncated each time
74 .It Fl deny_incoming | d
75 Do not pass incoming packets that have no
76 entry in the internal translation table.
78 If this option is not used, then such a packet will be altered
81 below, and the entry will be made in the internal translation table.
83 Log denied incoming packets via
89 .It Fl log_facility Ar facility_name
90 Use specified log facility when logging information via
94 is one of the keywords specified in
96 .It Fl use_sockets | s
99 in order to establish an FTP data or IRC DCC send connection.
100 This option uses more system resources, but guarantees successful
101 connections when port numbers conflict.
102 .It Fl same_ports | m
103 Try to keep the same port number when altering outgoing packets.
104 With this option, protocols such as RPC will have a better chance
106 If it is not possible to maintain the port number, it will be silently
107 changed as per normal.
111 on startup. Instead, stay attached to the controlling terminal and
112 display all packet alterations to the standard output. This option
113 should only be used for debugging purposes.
114 .It Fl unregistered_only | u
115 Only alter outgoing packets with an
118 According to RFC 1918, unregistered source addresses are 10.0.0.0/8,
119 172.16.0.0/12 and 192.168.0.0/16.
120 .It Fl redirect_port Ar proto Xo
121 .Ar targetIP Ns : Ns Xo
122 .Ar targetPORT Ns Op - Ns Ar targetPORT Xc
123 .Op Ar aliasIP Ns : Ns Xo
124 .Ar aliasPORT Ns Op - Ns Ar aliasPORT Xc
125 .Oo Ar remoteIP Ns Oo : Ns
126 .Ar remotePORT Ns Op - Ns Ar remotePORT
129 Redirect incoming connections arriving to given port(s) to another host
138 is the desired target IP number,
140 is the desired target port number or range,
142 is the requested port number or range, and
144 is the aliasing address.
149 can be used to specify the connection more accurately if necessary.
154 range need not be the same numerically, but must have the same size.
157 is not specified, it is assumed to be all ports.
160 is specified, it must match the size of
163 For example, the argument
165 .Dl Ar tcp inside1:telnet 6666
167 means that incoming TCP packets destined for port 6666 on this machine
168 will be sent to the telnet port on the inside1 machine.
170 .Dl Ar tcp inside2:2300-2399 3300-3399
172 will redirect incoming connections on ports 3300-3399 to host
173 inside2, ports 2300-2399.
174 The mapping is 1:1 meaning port 3300 maps to 2300, 3301 maps to 2301, etc.
175 .It Fl redirect_proto Ar proto localIP Oo
176 .Ar publicIP Op Ar remoteIP
178 Redirect incoming IP packets of protocol
180 .Po see Xr protocols 5
186 address and vice versa.
190 is not specified, then the default aliasing address is used.
193 is specified, then only packets coming from/to
196 .It Fl redirect_address Ar localIP publicIP
197 Redirect traffic for public IP address to a machine on the local
199 This function is known as
201 Normally static NAT is useful if your ISP has allocated a small block
202 of IP addresses to you, but it can even be used in the case of single
205 .Dl Ar redirect_address 10.0.0.8 0.0.0.0
207 The above command would redirect all incoming traffic
210 If several address aliases specify the same public address
212 .Bd -literal -offset indent
213 .Ar redirect_address 192.168.0.2 public_addr
214 .Ar redirect_address 192.168.0.3 public_addr
215 .Ar redirect_address 192.168.0.4 public_addr
218 the incoming traffic will be directed to the last
219 translated local address (192.168.0.4), but outgoing
220 traffic from the first two addresses will still be aliased
221 to appear from the specified
223 .It Fl redirect_port Ar proto Xo
224 .Ar targetIP Ns : Ns Xo
225 .Ar targetPORT Ns Oo , Ns
226 .Ar targetIP Ns : Ns Xo
227 .Ar targetPORT Ns Oo , Ns
232 .Op Ar aliasIP Ns : Ns Xo
236 .Op : Ns Ar remotePORT
239 .It Fl redirect_address Xo
240 .Ar localIP Ns Oo , Ns
241 .Ar localIP Ns Oo , Ns
250 are used to transparently offload network load on a single server and
251 distribute the load across a pool of servers.
252 This function is known as
255 For example, the argument
257 .Dl Ar tcp www1:http,www2:http,www3:http www:http
259 means that incoming HTTP requests for host www will be transparently
260 redirected to one of the www1, www2 or www3, where a host is selected
261 simply on a round-robin basis, without regard to load on the net.
269 will monitor the routing socket for alterations to the
272 If the interface's IP number is changed,
274 will dynamically alter its concept of the alias address.
275 .It Fl in_port | i Ar port
276 Read from and write to
280 treating all packets as
282 .It Fl out_port | o Ar port
283 Read from and write to
287 treating all packets as
289 .It Fl port | p Ar port
290 Read from and write to
294 distinguishing packets as
298 using the rules specified in
302 is not numeric, it is searched for in the
305 If this option is not specified, the divert port named
307 will be used as a default.
308 .It Fl alias_address | a Ar address
311 as the aliasing address.
312 If this option is not specified, the
315 The specified address is usually the address assigned to the
321 will be rewritten with a source address equal to
325 will be checked to see if it matches any already-aliased outgoing
327 If it does, the packet is altered accordingly.
333 assignments are checked and actioned.
334 If no other action can be made and if
336 is not specified, the packet is delivered to the local machine
337 using the rules specified in
340 .It Fl t | target_address Ar address
341 Set the target address.
342 When an incoming packet not associated with any pre-existing link
343 arrives at the host machine, it will be sent to the specified
346 The target address may be set to
347 .Ar 255.255.255.255 ,
348 in which case all new incoming packets go to the alias address set by
353 If this option is not used, or called with the argument
355 then all new incoming packets go to the address specified in
357 This allows external machines to talk directly to internal machines if
358 they can route packets to the machine in question.
359 .It Fl interface | n Ar interface
362 to determine the aliasing address.
363 If there is a possibility that the IP number associated with
367 option should also be used.
368 If this option is not specified, the
379 .It Fl config | f Ar file
380 Read configuration from
384 should contain a list of options, one per line, in the same form
385 as the long form of the above command line options.
386 For example, the line
388 .Dl alias_address 158.152.17.1
390 would specify an alias address of 158.152.17.1.
391 Options that do not take an argument are specified with an argument of
395 in the configuration file. For example, the line
400 Trailing spaces and empty lines are ignored.
403 sign will mark the rest of the line as a comment.
407 reverse the way it handles
411 packets, allowing it to operate on the
413 network interface rather than the
417 This can be useful in some transparent proxying situations
418 when outgoing traffic is redirected to the local machine
421 is running on the internal interface (it usually runs on the
426 to perform transparent proxying only.
427 Normal address translation is not performed.
429 .Op Ar type encode_ip_hdr | encode_tcp_stream
431 .Ar server a.b.c.d:yyyy
433 Enable transparent proxying.
434 Outgoing TCP packets with the given port going through this
435 host to any other host are redirected to the given server and port.
436 Optionally, the original target address can be encoded into the packet.
439 to put this information into the IP option field or
440 .Ar encode_tcp_stream
441 to inject the data into the beginning of the TCP stream.
443 .Ar basenumber Ns : Ns Ar count
451 based firewall for FTP/IRC DCC connections.
452 This is done dynamically by installing temporary firewall rules which
453 allow a particular connection (and only that connection) to go through
455 The rules are removed once the corresponding connection terminates.
459 rules starting from the rule number
461 will be used for punching firewall holes.
462 The range will be cleared for all rules on startup.
465 The following steps are necessary before attempting to run
469 Build a custom kernel with the following options:
470 .Bd -literal -offset indent
475 Refer to the handbook for detailed instructions on building a custom
478 Ensure that your machine is acting as a gateway.
479 This can be done by specifying the line
481 .Dl gateway_enable=YES
485 file or using the command
487 .Dl sysctl -w net.inet.ip.forwarding=1
492 option, make sure that your interface is already configured.
493 If, for example, you wish to specify
499 on that interface, you must make sure that you start
507 is fairly straight forward.
510 .Dl natd -interface en0
512 should suffice in most cases (substituting the correct interface name).
515 on how to configure it to be started automatically during boot.
518 is running, you must ensure that traffic is diverted to
522 You will need to adjust the
525 If you are not interested in having a firewall, the
526 following lines will do:
527 .Bd -literal -offset indent
529 /sbin/ipfw add divert natd all from any to any via ed0
530 /sbin/ipfw add pass all from any to any
533 The second line depends on your interface (change
537 You should be aware of the fact that, with these firewall settings,
538 everyone on your local network can fake his source-address using your
540 If there are other hosts on your local network, you are strongly
541 encouraged to create firewall rules that only allow traffic to and
544 If you specify real firewall rules, it is best to specify line 2 at
545 the start of the script so that
547 sees all packets before they are dropped by the firewall.
551 packets re-enter the firewall at the rule number following the rule number
552 that caused the diversion (not the next rule if there are several at the
555 Enable your firewall by setting
557 .Dl firewall_enable=YES
561 This tells the system startup scripts to run the
564 If you do not wish to reboot now, just run this by hand from the console.
565 NEVER run this from a remote session unless you put it into the background.
566 If you do, you will lock yourself out after the flush takes place, and
569 will stop at this point - blocking all accesses permanently.
570 Running the script in the background should be enough to prevent this
582 This program is the result of the efforts of many people at different
585 .An Archie Cobbs Aq archie@whistle.com
587 .An Charles Mott Aq cmott@scientech.com
589 .An Eivind Eklund Aq perhaps@yes.no
590 (IRC support & misc additions)
591 .An Ari Suutari Aq suutari@iki.fi
593 .An Dru Nelson Aq dnelson@redwoodsoft.com
595 .An Brian Somers Aq brian@awfulhak.org
597 .An Ruslan Ermilov Aq ru@FreeBSD.org
598 (natd, packet aliasing, glue)
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