7 .Nd Network Address Translation daemon
11 .Op Fl unregistered_only | u
15 .Op Fl deny_incoming | d
16 .Op Fl use_sockets | s
20 .Op Fl in_port | i Ar port
21 .Op Fl out_port | o Ar port
22 .Op Fl port | p Ar port
23 .Op Fl alias_address | a Ar address
24 .Op Fl target_address | t Ar address
25 .Op Fl interface | n Ar interface
26 .Op Fl proxy_rule Ar proxyspec
27 .Op Fl redirect_port Ar linkspec
28 .Op Fl redirect_proto Ar linkspec
29 .Op Fl redirect_address Ar linkspec
30 .Op Fl config | f Ar configfile
32 .Op Fl log_facility Ar facility_name
33 .Op Fl punch_fw Ar firewall_range
34 .Op Fl log_ipfw_denied
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
87 .It Fl log_facility Ar facility_name
88 Use specified log facility when logging information via
92 is one of the keywords specified in
94 .It Fl use_sockets | s
97 in order to establish an FTP data or IRC DCC send connection.
98 This option uses more system resources, but guarantees successful
99 connections when port numbers conflict.
100 .It Fl same_ports | m
101 Try to keep the same port number when altering outgoing packets.
102 With this option, protocols such as RPC will have a better chance
104 If it is not possible to maintain the port number, it will be silently
105 changed as per normal.
110 Instead, stay attached to the controlling terminal and display all packet
111 alterations to the standard output.
112 This option should only be used for debugging purposes.
113 .It Fl unregistered_only | u
114 Only alter outgoing packets with an
117 According to RFC 1918, unregistered source addresses are 10.0.0.0/8,
118 172.16.0.0/12 and 192.168.0.0/16.
119 .It Fl redirect_port Ar proto Xo
120 .Ar targetIP Ns : Ns Xo
121 .Ar targetPORT Ns Op - Ns Ar targetPORT Xc
122 .Op Ar aliasIP Ns : Ns Xo
123 .Ar aliasPORT Ns Op - Ns Ar aliasPORT Xc
124 .Oo Ar remoteIP Ns Oo : Ns
125 .Ar remotePORT Ns Op - Ns Ar remotePORT
128 Redirect incoming connections arriving to given port(s) to another host
137 is the desired target IP number,
139 is the desired target port number or range,
141 is the requested port number or range, and
143 is the aliasing address.
148 can be used to specify the connection more accurately if necessary.
153 range need not be the same numerically, but must have the same size.
156 is not specified, it is assumed to be all ports.
159 is specified, it must match the size of
162 For example, the argument
164 .Dl Ar tcp inside1:telnet 6666
166 means that incoming TCP packets destined for port 6666 on this machine
167 will be sent to the telnet port on the inside1 machine.
169 .Dl Ar tcp inside2:2300-2399 3300-3399
171 will redirect incoming connections on ports 3300-3399 to host
172 inside2, ports 2300-2399.
173 The mapping is 1:1 meaning port 3300 maps to 2300, 3301 maps to 2301, etc.
174 .It Fl redirect_proto Ar proto localIP Oo
175 .Ar publicIP Op Ar remoteIP
177 Redirect incoming IP packets of protocol
185 address and vice versa.
189 is not specified, then the default aliasing address is used.
192 is specified, then only packets coming from/to
195 .It Fl redirect_address Ar localIP publicIP
196 Redirect traffic for public IP address to a machine on the local
198 This function is known as
200 Normally static NAT is useful if your ISP has allocated a small block
201 of IP addresses to you, but it can even be used in the case of single
204 .Dl Ar redirect_address 10.0.0.8 0.0.0.0
206 The above command would redirect all incoming traffic
209 If several address aliases specify the same public address
211 .Bd -literal -offset indent
212 .Ar redirect_address 192.168.0.2 public_addr
213 .Ar redirect_address 192.168.0.3 public_addr
214 .Ar redirect_address 192.168.0.4 public_addr
217 the incoming traffic will be directed to the last
218 translated local address (192.168.0.4), but outgoing
219 traffic from the first two addresses will still be aliased
220 to appear from the specified
222 .It Fl redirect_port Ar proto Xo
223 .Ar targetIP Ns : Ns Xo
224 .Ar targetPORT Ns Oo , Ns
225 .Ar targetIP Ns : Ns Xo
226 .Ar targetPORT Ns Oo , Ns
231 .Op Ar aliasIP Ns : Ns Xo
235 .Op : Ns Ar remotePORT
238 .It Fl redirect_address Xo
239 .Ar localIP Ns Oo , Ns
240 .Ar localIP Ns Oo , Ns
249 are used to transparently offload network load on a single server and
250 distribute the load across a pool of servers.
251 This function is known as
254 For example, the argument
256 .Dl Ar tcp www1:http,www2:http,www3:http www:http
258 means that incoming HTTP requests for host www will be transparently
259 redirected to one of the www1, www2 or www3, where a host is selected
260 simply on a round-robin basis, without regard to load on the net.
268 will monitor the routing socket for alterations to the
271 If the interface's IP number is changed,
273 will dynamically alter its concept of the alias address.
274 .It Fl in_port | i Ar port
275 Read from and write to
279 treating all packets as
281 .It Fl out_port | o Ar port
282 Read from and write to
286 treating all packets as
288 .It Fl port | p Ar port
289 Read from and write to
293 distinguishing packets as
297 using the rules specified in
301 is not numeric, it is searched for in the
304 If this option is not specified, the divert port named
306 will be used as a default.
307 .It Fl alias_address | a Ar address
310 as the aliasing address.
311 If this option is not specified, the
314 The specified address is usually the address assigned to the
320 will be rewritten with a source address equal to
324 will be checked to see if it matches any already-aliased outgoing
326 If it does, the packet is altered accordingly.
332 assignments are checked and actioned.
333 If no other action can be made and if
335 is not specified, the packet is delivered to the local machine
336 using the rules specified in
339 .It Fl t | target_address Ar address
340 Set the target address.
341 When an incoming packet not associated with any pre-existing link
342 arrives at the host machine, it will be sent to the specified
345 The target address may be set to
346 .Ar 255.255.255.255 ,
347 in which case all new incoming packets go to the alias address set by
352 If this option is not used, or called with the argument
354 then all new incoming packets go to the address specified in
356 This allows external machines to talk directly to internal machines if
357 they can route packets to the machine in question.
358 .It Fl interface | n Ar interface
361 to determine the aliasing address.
362 If there is a possibility that the IP number associated with
366 option should also be used.
367 If this option is not specified, the
378 .It Fl config | f Ar file
379 Read configuration from
383 should contain a list of options, one per line, in the same form
384 as the long form of the above command line options.
385 For example, the line
387 .Dl alias_address 158.152.17.1
389 would specify an alias address of 158.152.17.1.
390 Options that do not take an argument are specified with an argument of
394 in the configuration file.
395 For example, the line
402 Trailing spaces and empty lines are ignored.
405 sign will mark the rest of the line as a comment.
409 reverse the way it handles
413 packets, allowing it to operate on the
415 network interface rather than the
419 This can be useful in some transparent proxying situations
420 when outgoing traffic is redirected to the local machine
423 is running on the internal interface (it usually runs on the
428 to perform transparent proxying only.
429 Normal address translation is not performed.
431 .Op Ar type encode_ip_hdr | encode_tcp_stream
433 .Ar server a.b.c.d:yyyy
435 Enable transparent proxying.
436 Outgoing TCP packets with the given port going through this
437 host to any other host are redirected to the given server and port.
438 Optionally, the original target address can be encoded into the packet.
441 to put this information into the IP option field or
442 .Ar encode_tcp_stream
443 to inject the data into the beginning of the TCP stream.
445 .Ar basenumber Ns : Ns Ar count
453 based firewall for FTP/IRC DCC connections.
454 This is done dynamically by installing temporary firewall rules which
455 allow a particular connection (and only that connection) to go through
457 The rules are removed once the corresponding connection terminates.
461 rules starting from the rule number
463 will be used for punching firewall holes.
464 The range will be cleared for all rules on startup.
465 .It Fl log_ipfw_denied
466 Log when a packet can not be re-injected because an
469 This is the default with
473 The following steps are necessary before attempting to run
477 Build a custom kernel with the following options:
478 .Bd -literal -offset indent
483 Refer to the handbook for detailed instructions on building a custom
486 Ensure that your machine is acting as a gateway.
487 This can be done by specifying the line
489 .Dl gateway_enable=YES
493 file or using the command
495 .Dl "sysctl net.inet.ip.forwarding=1"
500 option, make sure that your interface is already configured.
501 If, for example, you wish to specify
507 on that interface, you must make sure that you start
515 is fairly straight forward.
518 .Dl natd -interface ed0
520 should suffice in most cases (substituting the correct interface name).
523 on how to configure it to be started automatically during boot.
526 is running, you must ensure that traffic is diverted to
530 You will need to adjust the
533 If you are not interested in having a firewall, the
534 following lines will do:
535 .Bd -literal -offset indent
537 /sbin/ipfw add divert natd all from any to any via ed0
538 /sbin/ipfw add pass all from any to any
541 The second line depends on your interface (change
545 You should be aware of the fact that, with these firewall settings,
546 everyone on your local network can fake his source-address using your
548 If there are other hosts on your local network, you are strongly
549 encouraged to create firewall rules that only allow traffic to and
552 If you specify real firewall rules, it is best to specify line 2 at
553 the start of the script so that
555 sees all packets before they are dropped by the firewall.
559 packets re-enter the firewall at the rule number following the rule number
560 that caused the diversion (not the next rule if there are several at the
563 Enable your firewall by setting
565 .Dl firewall_enable=YES
569 This tells the system startup scripts to run the
572 If you do not wish to reboot now, just run this by hand from the console.
573 NEVER run this from a remote session unless you put it into the background.
574 If you do, you will lock yourself out after the flush takes place, and
577 will stop at this point - blocking all accesses permanently.
578 Running the script in the background should be enough to prevent this
590 This program is the result of the efforts of many people at different
593 .An Archie Cobbs Aq archie@whistle.com
595 .An Charles Mott Aq cmott@scientech.com
597 .An Eivind Eklund Aq perhaps@yes.no
598 (IRC support & misc additions)
599 .An Ari Suutari Aq suutari@iki.fi
601 .An Dru Nelson Aq dnelson@redwoodsoft.com
603 .An Brian Somers Aq brian@awfulhak.org
605 .An Ruslan Ermilov Aq ru@FreeBSD.org
606 (natd, packet aliasing, glue)
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