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1 .\" $FreeBSD: src/sbin/natd/natd.8,v 1.27.2.13 2003/02/23 21:17:43 trhodes Exp $
2 .\" $DragonFly: src/sbin/natd/natd.8,v 1.3 2004/03/11 12:28:54 hmp Exp $
3 .Dd June 27, 2000
4 .Dt NATD 8
5 .Os
6 .Sh NAME
7 .Nm natd
8 .Nd Network Address Translation daemon
9 .Sh SYNOPSIS
10 .Nm
11 .Bk -words
12 .Op Fl unregistered_only | u
13 .Op Fl log | l
14 .Op Fl proxy_only
15 .Op Fl reverse
16 .Op Fl deny_incoming | d
17 .Op Fl use_sockets | s
18 .Op Fl same_ports | m
19 .Op Fl verbose | v
20 .Op Fl dynamic
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
32 .Op Fl log_denied
33 .Op Fl log_facility Ar facility_name
34 .Op Fl punch_fw Ar firewall_range
35 .Op Fl log_ipfw_denied
36 .Ek
37 .Sh DESCRIPTION
38 The
39 .Nm
40 utility provides a Network Address Translation facility for use
41 with
42 .Xr divert 4
43 sockets under
44 .Dx .
45 It is intended for use with NICs - if you want to do NAT on a PPP link,
46 use the
47 .Fl nat
48 switch to
49 .Xr ppp 8 .
50 .Pp
51 The
52 .Nm
53 utility normally runs in the background as a daemon.
54 It is passed raw IP packets as they travel into and out of the machine,
55 and will possibly change these before re-injecting them back into the
56 IP packet stream.
57 .Pp
58 It changes all packets destined for another host so that their source
59 IP number is that of the current machine.
60 For each packet changed in this manner, an internal table entry is
61 created to record this fact.
62 The source port number is also changed to indicate the table entry
63 applying to the packet.
64 Packets that are received with a target IP of the current host are
65 checked against this internal table.
66 If an entry is found, it is used to determine the correct target IP
67 number and port to place in the packet.
68 .Pp
69 The following command line options are available:
70 .Bl -tag -width Fl
71 .It Fl log | l
72 Log various aliasing statistics and information to the file
73 .Pa /var/log/alias.log .
74 This file is truncated each time
75 .Nm
76 is started.
77 .It Fl deny_incoming | d
78 Do not pass incoming packets that have no
79 entry in the internal translation table.
80 .Pp
81 If this option is not used, then such a packet will be altered
82 using the rules in
83 .Fl target_address
84 below, and the entry will be made in the internal translation table.
85 .It Fl log_denied
86 Log denied incoming packets via
87 .Xr syslog 3
88 (see also
89 .Fl log_facility ) .
90 .It Fl log_facility Ar facility_name
91 Use specified log facility when logging information via
92 .Xr syslog 3 .
93 Argument
94 .Ar facility_name
95 is one of the keywords specified in
96 .Xr syslog.conf 5 .
97 .It Fl use_sockets | s
98 Allocate a
99 .Xr socket 2
100 in order to establish an FTP data or IRC DCC send connection.
101 This option uses more system resources, but guarantees successful
102 connections when port numbers conflict.
103 .It Fl same_ports | m
104 Try to keep the same port number when altering outgoing packets.
105 With this option, protocols such as RPC will have a better chance
106 of working.
107 If it is not possible to maintain the port number, it will be silently
108 changed as per normal.
109 .It Fl verbose | v
110 Do not call
111 .Xr daemon 3
112 on startup.
113 Instead, stay attached to the controlling terminal and display all packet
114 alterations to the standard output.
115 This option should only be used for debugging purposes.
116 .It Fl unregistered_only | u
117 Only alter outgoing packets with an
118 .Em unregistered
119 source address.
120 According to RFC 1918, unregistered source addresses are 10.0.0.0/8,
121 172.16.0.0/12 and 192.168.0.0/16.
122 .It Fl redirect_port Ar proto Xo
123 .Ar targetIP Ns : Ns Xo
124 .Ar targetPORT Ns Op - Ns Ar targetPORT Xc
125 .Op Ar aliasIP Ns : Ns Xo
126 .Ar aliasPORT Ns Op - Ns Ar aliasPORT Xc
127 .Oo Ar remoteIP Ns Oo : Ns
128 .Ar remotePORT Ns Op - Ns Ar remotePORT
129 .Oc Oc
130 .Xc
131 Redirect incoming connections arriving to given port(s) to another host
132 and port(s).
133 Argument
134 .Ar proto
135 is either
136 .Ar tcp
137 or
138 .Ar udp ,
139 .Ar targetIP
140 is the desired target IP number,
141 .Ar targetPORT
142 is the desired target port number or range,
143 .Ar aliasPORT
144 is the requested port number or range, and
145 .Ar aliasIP
146 is the aliasing address.
147 Arguments
148 .Ar remoteIP
149 and
150 .Ar remotePORT
151 can be used to specify the connection more accurately if necessary.
152 The
153 .Ar targetPORT
154 range and
155 .Ar aliasPORT
156 range need not be the same numerically, but must have the same size.
157 If
158 .Ar remotePORT
159 is not specified, it is assumed to be all ports.
160 If
161 .Ar remotePORT
162 is specified, it must match the size of
163 .Ar targetPORT ,
164 or be 0 (all ports).
165 For example, the argument
166 .Pp
167 .Dl Ar tcp inside1:telnet 6666
168 .Pp
169 means that incoming TCP packets destined for port 6666 on this machine
170 will be sent to the telnet port on the inside1 machine.
171 .Pp
172 .Dl Ar tcp inside2:2300-2399 3300-3399
173 .Pp
174 will redirect incoming connections on ports 3300-3399 to host
175 inside2, ports 2300-2399.
176 The mapping is 1:1 meaning port 3300 maps to 2300, 3301 maps to 2301, etc.
177 .It Fl redirect_proto Ar proto localIP Oo
178 .Ar publicIP Op Ar remoteIP
179 .Oc
180 Redirect incoming IP packets of protocol
181 .Ar proto
182 (see
183 .Xr protocols 5 )
184 destined for
185 .Ar publicIP
186 address to a
187 .Ar localIP
188 address and vice versa.
189 .Pp
190 If
191 .Ar publicIP
192 is not specified, then the default aliasing address is used.
193 If
194 .Ar remoteIP
195 is specified, then only packets coming from/to
196 .Ar remoteIP
197 will match the rule.
198 .It Fl redirect_address Ar localIP publicIP
199 Redirect traffic for public IP address to a machine on the local
200 network.
201 This function is known as
202 .Em static NAT .
203 Normally static NAT is useful if your ISP has allocated a small block
204 of IP addresses to you, but it can even be used in the case of single
205 address:
206 .Pp
207 .Dl Ar redirect_address 10.0.0.8 0.0.0.0
208 .Pp
209 The above command would redirect all incoming traffic
210 to machine 10.0.0.8.
211 .Pp
212 If several address aliases specify the same public address
213 as follows
214 .Bd -literal -offset indent
215 .Ar redirect_address 192.168.0.2 public_addr
216 .Ar redirect_address 192.168.0.3 public_addr
217 .Ar redirect_address 192.168.0.4 public_addr
218 .Ed
219 .Pp
220 the incoming traffic will be directed to the last
221 translated local address (192.168.0.4), but outgoing
222 traffic from the first two addresses will still be aliased
223 to appear from the specified
224 .Ar public_addr .
225 .It Fl redirect_port Ar proto Xo
226 .Ar targetIP Ns : Ns Xo
227 .Ar targetPORT Ns Oo , Ns
228 .Ar targetIP Ns : Ns Xo
229 .Ar targetPORT Ns Oo , Ns
230 .Ar ...\&
231 .Oc Oc
232 .Xc
233 .Xc
234 .Op Ar aliasIP Ns : Ns Xo
235 .Ar aliasPORT
236 .Xc
237 .Oo Ar remoteIP Ns
238 .Op : Ns Ar remotePORT
239 .Oc
240 .Xc
241 .It Fl redirect_address Xo
242 .Ar localIP Ns Oo , Ns
243 .Ar localIP Ns Oo , Ns
244 .Ar ...\&
245 .Oc Oc
246 .Ar publicIP
247 .Xc
248 These forms of
249 .Fl redirect_port
250 and
251 .Fl redirect_address
252 are used to transparently offload network load on a single server and
253 distribute the load across a pool of servers.
254 This function is known as
255 .Em LSNAT
256 (RFC 2391).
257 For example, the argument
258 .Pp
259 .Dl Ar tcp www1:http,www2:http,www3:http www:http
260 .Pp
261 means that incoming HTTP requests for host www will be transparently
262 redirected to one of the www1, www2 or www3, where a host is selected
263 simply on a round-robin basis, without regard to load on the net.
264 .It Fl dynamic
265 If the
266 .Fl n
267 or
268 .Fl interface
269 option is used,
270 .Nm
271 will monitor the routing socket for alterations to the
272 .Ar interface
273 passed.
274 If the interface's IP number is changed,
275 .Nm
276 will dynamically alter its concept of the alias address.
277 .It Fl in_port | i Ar port
278 Read from and write to
279 .Xr divert 4
280 port
281 .Ar port ,
282 treating all packets as
283 .Dq incoming .
284 .It Fl out_port | o Ar port
285 Read from and write to
286 .Xr divert 4
287 port
288 .Ar port ,
289 treating all packets as
290 .Dq outgoing .
291 .It Fl port | p Ar port
292 Read from and write to
293 .Xr divert 4
294 port
295 .Ar port ,
296 distinguishing packets as
297 .Dq incoming
298 or
299 .Dq outgoing
300 using the rules specified in
301 .Xr divert 4 .
302 If
303 .Ar port
304 is not numeric, it is searched for in the
305 .Xr services 5
306 database.
307 If this option is not specified, the divert port named
308 .Ar natd
309 will be used as a default.
310 .It Fl alias_address | a Ar address
311 Use
312 .Ar address
313 as the aliasing address.
314 If this option is not specified, the
315 .Fl interface
316 option must be used.
317 The specified address is usually the address assigned to the
318 .Dq public
319 network interface.
320 .Pp
321 All data passing
322 .Em out
323 will be rewritten with a source address equal to
324 .Ar address .
325 All data coming
326 .Em in
327 will be checked to see if it matches any already-aliased outgoing
328 connection.
329 If it does, the packet is altered accordingly.
330 If not, all
331 .Fl redirect_port ,
332 .Fl redirect_proto
333 and
334 .Fl redirect_address
335 assignments are checked and actioned.
336 If no other action can be made and if
337 .Fl deny_incoming
338 is not specified, the packet is delivered to the local machine
339 using the rules specified in
340 .Fl target_address
341 option below.
342 .It Fl t | target_address Ar address
343 Set the target address.
344 When an incoming packet not associated with any pre-existing link
345 arrives at the host machine, it will be sent to the specified
346 .Ar address .
347 .Pp
348 The target address may be set to
349 .Ar 255.255.255.255 ,
350 in which case all new incoming packets go to the alias address set by
351 .Fl alias_address
352 or
353 .Fl interface .
354 .Pp
355 If this option is not used, or called with the argument
356 .Ar 0.0.0.0 ,
357 then all new incoming packets go to the address specified in
358 the packet.
359 This allows external machines to talk directly to internal machines if
360 they can route packets to the machine in question.
361 .It Fl interface | n Ar interface
362 Use
363 .Ar interface
364 to determine the aliasing address.
365 If there is a possibility that the IP number associated with
366 .Ar interface
367 may change, the
368 .Fl dynamic
369 option should also be used.
370 If this option is not specified, the
371 .Fl alias_address
372 option must be used.
373 .Pp
374 The specified
375 .Ar interface
376 is usually the
377 .Dq public
378 (or
379 .Dq external )
380 network interface.
381 .It Fl config | f Ar file
382 Read configuration from
383 .Ar file .
384 A
385 .Ar file
386 should contain a list of options, one per line, in the same form
387 as the long form of the above command line options.
388 For example, the line
389 .Pp
390 .Dl alias_address 158.152.17.1
391 .Pp
392 would specify an alias address of 158.152.17.1.
393 Options that do not take an argument are specified with an argument of
394 .Ar yes
395 or
396 .Ar no
397 in the configuration file.
398 For example, the line
399 .Pp
400 .Dl log yes
401 .Pp
402 is synonymous with
403 .Fl log .
404 .Pp
405 Trailing spaces and empty lines are ignored.
406 A
407 .Ql \&#
408 sign will mark the rest of the line as a comment.
409 .It Fl reverse
410 This option makes
411 .Nm
412 reverse the way it handles
413 .Dq incoming
414 and
415 .Dq outgoing
416 packets, allowing it to operate on the
417 .Dq internal
418 network interface rather than the
419 .Dq external
420 one.
421 .Pp
422 This can be useful in some transparent proxying situations
423 when outgoing traffic is redirected to the local machine
424 and
425 .Nm
426 is running on the internal interface (it usually runs on the
427 external interface).
428 .It Fl proxy_only
429 Force
430 .Nm
431 to perform transparent proxying only.
432 Normal address translation is not performed.
433 .It Fl proxy_rule Xo
434 .Op Ar type encode_ip_hdr | encode_tcp_stream
435 .Ar port xxxx
436 .Ar server a.b.c.d:yyyy
437 .Xc
438 Enable transparent proxying.
439 Outgoing TCP packets with the given port going through this
440 host to any other host are redirected to the given server and port.
441 Optionally, the original target address can be encoded into the packet.
442 Use
443 .Ar encode_ip_hdr
444 to put this information into the IP option field or
445 .Ar encode_tcp_stream
446 to inject the data into the beginning of the TCP stream.
447 .It Fl punch_fw Xo
448 .Ar basenumber Ns : Ns Ar count
449 .Xc
450 This option directs
451 .Nm
452 to
453 .Dq punch holes
454 in an
455 .Xr ipfirewall 4
456 based firewall for FTP/IRC DCC connections.
457 This is done dynamically by installing temporary firewall rules which
458 allow a particular connection (and only that connection) to go through
459 the firewall.
460 The rules are removed once the corresponding connection terminates.
461 .Pp
462 A maximum of
463 .Ar count
464 rules starting from the rule number
465 .Ar basenumber
466 will be used for punching firewall holes.
467 The range will be cleared for all rules on startup.
468 .It Fl log_ipfw_denied
469 Log when a packet cannot be re-injected because an
470 .Xr ipfw 8
471 rule blocks it.
472 This is the default with
473 .Fl verbose .
474 .El
475 .Sh RUNNING NATD
476 The following steps are necessary before attempting to run
477 .Nm :
478 .Bl -enum
479 .It
480 Build a custom kernel with the following options:
481 .Bd -literal -offset indent
482 options IPFIREWALL
483 options IPDIVERT
484 .Ed
485 .Pp
486 Refer to the handbook for detailed instructions on building a custom
487 kernel.
488 .It
489 Ensure that your machine is acting as a gateway.
490 This can be done by specifying the line
491 .Pp
492 .Dl gateway_enable=YES
493 .Pp
494 in the
495 .Pa /etc/rc.conf
496 file or using the command
497 .Pp
498 .Dl "sysctl net.inet.ip.forwarding=1"
499 .Pp
500 .It
501 If you use the
502 .Fl interface
503 option, make sure that your interface is already configured.
504 If, for example, you wish to specify
505 .Ql tun0
506 as your
507 .Ar interface ,
508 and you are using
509 .Xr ppp 8
510 on that interface, you must make sure that you start
511 .Nm ppp
512 prior to starting
513 .Nm .
514 .El
515 .Pp
516 Running
517 .Nm
518 is fairly straight forward.
519 The line
520 .Pp
521 .Dl natd -interface ed0
522 .Pp
523 should suffice in most cases (substituting the correct interface name).
524 Please check
525 .Xr rc.conf 5
526 on how to configure it to be started automatically during boot.
527 Once
528 .Nm
529 is running, you must ensure that traffic is diverted to
530 .Nm :
531 .Bl -enum
532 .It
533 You will need to adjust the
534 .Pa /etc/rc.firewall
535 script to taste.
536 If you are not interested in having a firewall, the
537 following lines will do:
538 .Bd -literal -offset indent
539 /sbin/ipfw -f flush
540 /sbin/ipfw add divert natd all from any to any via ed0
541 /sbin/ipfw add pass all from any to any
542 .Ed
543 .Pp
544 The second line depends on your interface (change
545 .Ql ed0
546 as appropriate).
547 .Pp
548 You should be aware of the fact that, with these firewall settings,
549 everyone on your local network can fake his source-address using your
550 host as gateway.
551 If there are other hosts on your local network, you are strongly
552 encouraged to create firewall rules that only allow traffic to and
553 from trusted hosts.
554 .Pp
555 If you specify real firewall rules, it is best to specify line 2 at
556 the start of the script so that
557 .Nm
558 sees all packets before they are dropped by the firewall.
559 .Pp
560 After translation by
561 .Nm ,
562 packets re-enter the firewall at the rule number following the rule number
563 that caused the diversion (not the next rule if there are several at the
564 same number).
565 .It
566 Enable your firewall by setting
567 .Pp
568 .Dl firewall_enable=YES
569 .Pp
570 in
571 .Pa /etc/rc.conf .
572 This tells the system startup scripts to run the
573 .Pa /etc/rc.firewall
574 script.
575 If you do not wish to reboot now, just run this by hand from the console.
576 NEVER run this from a remote session unless you put it into the background.
577 If you do, you will lock yourself out after the flush takes place, and
578 execution of
579 .Pa /etc/rc.firewall
580 will stop at this point - blocking all accesses permanently.
581 Running the script in the background should be enough to prevent this
582 disaster.
583 .El
584 .Sh SEE ALSO
585 .Xr divert 4 ,
586 .Xr protocols 5 ,
587 .Xr rc.conf 5 ,
588 .Xr services 5 ,
589 .Xr syslog.conf 5 ,
590 .Xr ipfw 8 ,
591 .Xr ppp 8
592 .Sh AUTHORS
593 This program is the result of the efforts of many people at different
594 times:
595 .Pp
596 .An Archie Cobbs Aq archie@FreeBSD.org
597 (divert sockets)
598 .An Charles Mott Aq cmott@scientech.com
599 (packet aliasing)
600 .An Eivind Eklund Aq perhaps@yes.no
601 (IRC support & misc additions)
602 .An Ari Suutari Aq suutari@iki.fi
603 (natd)
604 .An Dru Nelson Aq dnelson@redwoodsoft.com
605 (early PPTP support)
606 .An Brian Somers Aq brian@awfulhak.org
607 (glue)
608 .An Ruslan Ermilov Aq ru@FreeBSD.org
609 (natd, packet aliasing, glue)