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 $
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
35 .Op Fl log_ipfw_denied
40 utility provides a Network Address Translation facility for use
45 It is intended for use with NICs - if you want to do NAT on a PPP link,
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
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.
69 The following command line options are available:
72 Log various aliasing statistics and information to the file
73 .Pa /var/log/alias.log .
74 This file is truncated each time
77 .It Fl deny_incoming | d
78 Do not pass incoming packets that have no
79 entry in the internal translation table.
81 If this option is not used, then such a packet will be altered
84 below, and the entry will be made in the internal translation table.
86 Log denied incoming packets via
90 .It Fl log_facility Ar facility_name
91 Use specified log facility when logging information via
95 is one of the keywords specified in
97 .It Fl use_sockets | s
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
107 If it is not possible to maintain the port number, it will be silently
108 changed as per normal.
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
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
131 Redirect incoming connections arriving to given port(s) to another host
140 is the desired target IP number,
142 is the desired target port number or range,
144 is the requested port number or range, and
146 is the aliasing address.
151 can be used to specify the connection more accurately if necessary.
156 range need not be the same numerically, but must have the same size.
159 is not specified, it is assumed to be all ports.
162 is specified, it must match the size of
165 For example, the argument
167 .Dl Ar tcp inside1:telnet 6666
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.
172 .Dl Ar tcp inside2:2300-2399 3300-3399
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
180 Redirect incoming IP packets of protocol
188 address and vice versa.
192 is not specified, then the default aliasing address is used.
195 is specified, then only packets coming from/to
198 .It Fl redirect_address Ar localIP publicIP
199 Redirect traffic for public IP address to a machine on the local
201 This function is known as
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
207 .Dl Ar redirect_address 10.0.0.8 0.0.0.0
209 The above command would redirect all incoming traffic
212 If several address aliases specify the same public address
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
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
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
234 .Op Ar aliasIP Ns : Ns Xo
238 .Op : Ns Ar remotePORT
241 .It Fl redirect_address Xo
242 .Ar localIP Ns Oo , Ns
243 .Ar localIP Ns Oo , Ns
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
257 For example, the argument
259 .Dl Ar tcp www1:http,www2:http,www3:http www:http
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.
271 will monitor the routing socket for alterations to the
274 If the interface's IP number is changed,
276 will dynamically alter its concept of the alias address.
277 .It Fl in_port | i Ar port
278 Read from and write to
282 treating all packets as
284 .It Fl out_port | o Ar port
285 Read from and write to
289 treating all packets as
291 .It Fl port | p Ar port
292 Read from and write to
296 distinguishing packets as
300 using the rules specified in
304 is not numeric, it is searched for in the
307 If this option is not specified, the divert port named
309 will be used as a default.
310 .It Fl alias_address | a Ar address
313 as the aliasing address.
314 If this option is not specified, the
317 The specified address is usually the address assigned to the
323 will be rewritten with a source address equal to
327 will be checked to see if it matches any already-aliased outgoing
329 If it does, the packet is altered accordingly.
335 assignments are checked and actioned.
336 If no other action can be made and if
338 is not specified, the packet is delivered to the local machine
339 using the rules specified in
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
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
355 If this option is not used, or called with the argument
357 then all new incoming packets go to the address specified in
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
364 to determine the aliasing address.
365 If there is a possibility that the IP number associated with
369 option should also be used.
370 If this option is not specified, the
381 .It Fl config | f Ar file
382 Read configuration from
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
390 .Dl alias_address 158.152.17.1
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
397 in the configuration file.
398 For example, the line
405 Trailing spaces and empty lines are ignored.
408 sign will mark the rest of the line as a comment.
412 reverse the way it handles
416 packets, allowing it to operate on the
418 network interface rather than the
422 This can be useful in some transparent proxying situations
423 when outgoing traffic is redirected to the local machine
426 is running on the internal interface (it usually runs on the
431 to perform transparent proxying only.
432 Normal address translation is not performed.
434 .Op Ar type encode_ip_hdr | encode_tcp_stream
436 .Ar server a.b.c.d:yyyy
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.
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.
448 .Ar basenumber Ns : Ns Ar count
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
460 The rules are removed once the corresponding connection terminates.
464 rules starting from the rule number
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
472 This is the default with
476 The following steps are necessary before attempting to run
480 Build a custom kernel with the following options:
481 .Bd -literal -offset indent
486 Refer to the handbook for detailed instructions on building a custom
489 Ensure that your machine is acting as a gateway.
490 This can be done by specifying the line
492 .Dl gateway_enable=YES
496 file or using the command
498 .Dl "sysctl net.inet.ip.forwarding=1"
503 option, make sure that your interface is already configured.
504 If, for example, you wish to specify
510 on that interface, you must make sure that you start
518 is fairly straight forward.
521 .Dl natd -interface ed0
523 should suffice in most cases (substituting the correct interface name).
526 on how to configure it to be started automatically during boot.
529 is running, you must ensure that traffic is diverted to
533 You will need to adjust the
536 If you are not interested in having a firewall, the
537 following lines will do:
538 .Bd -literal -offset indent
540 /sbin/ipfw add divert natd all from any to any via ed0
541 /sbin/ipfw add pass all from any to any
544 The second line depends on your interface (change
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
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
555 If you specify real firewall rules, it is best to specify line 2 at
556 the start of the script so that
558 sees all packets before they are dropped by the firewall.
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
566 Enable your firewall by setting
568 .Dl firewall_enable=YES
572 This tells the system startup scripts to run the
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
580 will stop at this point - blocking all accesses permanently.
581 Running the script in the background should be enough to prevent this
593 This program is the result of the efforts of many people at different
596 .An Archie Cobbs Aq archie@FreeBSD.org
598 .An Charles Mott Aq cmott@scientech.com
600 .An Eivind Eklund Aq perhaps@yes.no
601 (IRC support & misc additions)
602 .An Ari Suutari Aq suutari@iki.fi
604 .An Dru Nelson Aq dnelson@redwoodsoft.com
606 .An Brian Somers Aq brian@awfulhak.org
608 .An Ruslan Ermilov Aq ru@FreeBSD.org
609 (natd, packet aliasing, glue)
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