1SSHUTTLE(1) sshuttle SSHUTTLE(1)
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6 sshuttle - sshuttle documentation
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9 sshuttle [options] -r [username@]sshserver[:port] <subnets ...>
10
12 sshuttle allows you to create a VPN connection from your machine to any
13 remote server that you can connect to via ssh, as long as that server
14 has a sufficiently new Python installation.
15 To work, you must have root access on the local machine, but you can
17 have a normal account on the server.
18 It's valid to run sshuttle more than once simultaneously on a single
20 client machine, connecting to a different server every time, so you can
21 be on more than one VPN at once.
22 If run on a router, sshuttle can forward traffic for your entire subnet
24 to the VPN.
25
27 <subnets>
28 A list of subnets to route over the VPN, in the form
29 a.b.c.d[/width][port[-port]]. Valid examples are 1.2.3.4 (a sin‐
30 gle IP address) and 1.2.3.4/32 (equivalent to 1.2.3.4),
31 1.2.3.0/24 (a 24-bit subnet, ie. with a 255.255.255.0 netmask).
32 Specify subnets 0/0 to match all IPv4 addresses and ::/0 to
33 match all IPv6 addresses. Any of the previous examples are also
34 valid if you append a port or a port range, so 1.2.3.4:8000 will
35 only tunnel traffic that has as the destination port 8000 of
36 1.2.3.4 and 1.2.3.0/24:8000-9000 will tunnel traffic going to
37 any port between 8000 and 9000 (inclusive) for all IPs in the
38 1.2.3.0/24 subnet. A hostname can be provided instead of an IP
39 address. If the hostname resolves to multiple IPs, all of the
40 IPs are included. If a width is provided with a hostname, the
41 width is applied to all of the hostnames IPs (if they are all
42 either IPv4 or IPv6). Widths cannot be supplied to hostnames
43 that resolve to both IPv4 and IPv6. Valid examples are exam‐
44 ple.com, example.com:8000, example.com/24, example.com/24:8000
45 and example.com:8000-9000.
46 --method <auto|nat|nft|tproxy|pf|ipfw>
48 Which firewall method should sshuttle use? For auto, sshuttle
49 attempts to guess the appropriate method depending on what it
50 can find in PATH. The default value is auto.
51 -l <[ip:]port>, --listen=<[ip:]port>
53 Use this ip address and port number as the transparent proxy
54 port. By default sshuttle finds an available port automatically
55 and listens on IP 127.0.0.1 (localhost), so you don't need to
56 override it, and connections are only proxied from the local ma‐
57 chine, not from outside machines. If you want to accept connec‐
58 tions from other machines on your network (ie. to run sshuttle
59 on a router) try enabling IP Forwarding in your kernel, then us‐
60 ing --listen 0.0.0.0:0. You can use any name resolving to an IP
61 address of the machine running sshuttle, e.g. --listen local‐
62 host.
63 For the nft, tproxy and pf methods this can be an IPv6 address.
65 Use this option with comma separated values if required, to pro‐
66 vide both IPv4 and IPv6 addresses, e.g. --listen
67 127.0.0.1:0,[::1]:0.
68 -H, --auto-hosts
70 Scan for remote hostnames and update the local /etc/hosts file
71 with matching entries for as long as the VPN is open. This is
72 nicer than changing your system's DNS (/etc/resolv.conf) set‐
73 tings, for several reasons. First, hostnames are added without
74 domain names attached, so you can ssh thatserver without worry‐
75 ing if your local domain matches the remote one. Second, if you
76 sshuttle into more than one VPN at a time, it's impossible to
77 use more than one DNS server at once anyway, but sshuttle cor‐
78 rectly merges /etc/hosts entries between all running copies.
79 Third, if you're only routing a few subnets over the VPN, you
80 probably would prefer to keep using your local DNS server for
81 everything else.
82 sshuttle tries to store a cache of the hostnames in ~/.sshut‐
84 tle.hosts on the remote host. Similarly, it tries to read the
85 file when you later reconnect to the host with --auto-hosts en‐
86 abled to quickly populate the host list. When troubleshooting
87 this feature, try removing this file on the remote host when
88 sshuttle is not running.
89 -N, --auto-nets
91 In addition to the subnets provided on the command line, ask the
92 server which subnets it thinks we should route, and route those
93 automatically. The suggestions are taken automatically from the
94 server's routing table.
95 This feature does not detect IPv6 routes. Specify IPv6 subnets
97 manually. For example, specify the ::/0 subnet on the command
98 line to route all IPv6 traffic.
99 --dns Capture local DNS requests and forward to the remote DNS server.
101 All queries to any of the local system's DNS servers (/etc/re‐
102 solv.conf and, if it exists, /run/systemd/resolve/resolv.conf)
103 will be intercepted and resolved on the remote side of the tun‐
104 nel instead, there using the DNS specified via the --to-ns op‐
105 tion, if specified. Only plain DNS traffic sent to these servers
106 on port 53 are captured.
107 --ns-hosts=<server1[,server2[,server3[...]]]>
109 Capture local DNS requests to the specified server(s) and for‐
110 ward to the remote DNS server. Contrary to the --dns option,
111 this flag allows to specify the DNS server(s) the queries to
112 which to intercept, instead of intercepting all DNS traffic on
113 the local machine. This can be useful when only certain DNS re‐
114 quests should be resolved on the remote side of the tunnel, e.g.
115 in combination with dnsmasq.
116 --to-ns=<server>
118 The DNS to forward requests to when remote DNS resolution is en‐
119 abled. If not given, sshuttle will simply resolve using the sys‐
120 tem configured resolver on the remote side (via /etc/resolv.conf
121 on the remote side).
122 --python
124 Specify the name/path of the remote python interpreter. The de‐
125 fault is to use python3 (or python, if python3 fails) in the re‐
126 mote system's PATH.
127 -r <[username@]sshserver[:port]>, --remote=<[username@]ssh‐
129 server[:port]>
130 The remote hostname and optional username and ssh port number to
131 use for connecting to the remote server. For example, exam‐
132 ple.com, testuser@example.com, testuser@example.com:2222, or ex‐
133 ample.com:2244. This hostname is passed to ssh, so it will rec‐
134 ognize any aliases and settings you may have configured in
135 ~/.ssh/config.
136 -x <subnet>, --exclude=<subnet>
138 Explicitly exclude this subnet from forwarding. The format of
139 this option is the same as the <subnets> option. To exclude
140 more than one subnet, specify the -x option more than once. You
141 can say something like 0/0 -x 1.2.3.0/24 to forward everything
142 except the local subnet over the VPN, for example.
143 -X <file>, --exclude-from=<file>
145 Exclude the subnets specified in a file, one subnet per line.
146 Useful when you have lots of subnets to exclude.
147 -v, --verbose
149 Print more information about the session. This option can be
150 used more than once for increased verbosity. By default, sshut‐
151 tle prints only error messages.
152 -e, --ssh-cmd
154 The command to use to connect to the remote server. The default
155 is just ssh. Use this if your ssh client is in a non-standard
156 location or you want to provide extra options to the ssh com‐
157 mand, for example, -e 'ssh -v'.
158 --seed-hosts
160 A comma-separated list of hostnames to use to initialize the
161 --auto-hosts scan algorithm. --auto-hosts does things like poll
162 netstat output for lists of local hostnames, but can speed
163 things up if you use this option to give it a few names to start
164 from.
165 If this option is used without --auto-hosts, then the listed
167 hostnames will be scanned and added, but no further hostnames
168 will be added.
169 --no-latency-control
171 Sacrifice latency to improve bandwidth benchmarks. ssh uses re‐
172 ally big socket buffers, which can overload the connection if
173 you start doing large file transfers, thus making all your other
174 sessions inside the same tunnel go slowly. Normally, sshuttle
175 tries to avoid this problem using a "fullness check" that allows
176 only a certain amount of outstanding data to be buffered at a
177 time. But on high-bandwidth links, this can leave a lot of your
178 bandwidth underutilized. It also makes sshuttle seem slow in
179 bandwidth benchmarks (benchmarks rarely test ping latency, which
180 is what sshuttle is trying to control). This option disables
181 the latency control feature, maximizing bandwidth usage. Use at
182 your own risk.
183 --latency-buffer-size
185 Set the size of the buffer used in latency control. The default
186 is 32768. Changing this option allows a compromise to be made
187 between latency and bandwidth without completely disabling la‐
188 tency control (with --no-latency-control).
189 -D, --daemon
191 Automatically fork into the background after connecting to the
192 remote server. Implies --syslog.
193 -s <file>, --subnets=<file>
195 Include the subnets specified in a file instead of on the com‐
196 mand line. One subnet per line.
197 --syslog
199 after connecting, send all log messages to the syslog(3) service
200 instead of stderr. This is implicit if you use --daemon.
201 --pidfile=<pidfilename>
203 when using --daemon, save sshuttle's pid to pidfilename. The
204 default is sshuttle.pid in the current directory.
205 --disable-ipv6
207 Disable IPv6 support for methods that support it (nat, nft,
208 tproxy, and pf).
209 --firewall
211 (internal use only) run the firewall manager. This is the only
212 part of sshuttle that must run as root. If you start sshuttle
213 as a non-root user, it will automatically run sudo or su to
214 start the firewall manager, but the core of sshuttle still runs
215 as a normal user.
216 --hostwatch
218 (internal use only) run the hostwatch daemon. This process runs
219 on the server side and collects hostnames for the --auto-hosts
220 option. Using this option by itself makes it a lot easier to
221 debug and test the --auto-hosts feature.
222 --sudoers-no-modify
224 sshuttle prints a configuration to stdout which allows a user to
225 run sshuttle without a password. This option is INSECURE be‐
226 cause, with some cleverness, it also allows the user to run any
227 command as root without a password. The output also includes a
228 suggested method for you to install the configuration.
229 Use --sudoers-user to modify the user that it applies to.
231 --sudoers-user
233 Set the user name or group with %group_name for passwordless op‐
234 eration. Default is the current user. Set to ALL for all users
235 (NOT RECOMMENDED: See note about security in --sudoers-no-modify
236 documentation above). Only works with the --sudoers-no-modify
237 option.
238 -t <mark>, --tmark=<mark>
240 An option used by the tproxy method: Use the specified traffic
241 mark. The mark must be a hexadecimal value. Defaults to 0x01.
242 --version
244 Print program version.
245
247 All the options described above can optionally be specified in a con‐
248 figuration file.
249 To run sshuttle with options defined in, e.g., /etc/sshuttle.conf just
251 pass the path to the file preceded by the @ character, e.g.
252 @/etc/sshuttle.conf.
253 When running sshuttle with options defined in a configuration file, op‐
255 tions can still be passed via the command line in addition to what is
256 defined in the file. If a given option is defined both in the file and
257 in the command line, the value in the command line will take prece‐
258 dence.
259 Arguments read from a file must be one per line, as shown below:
261 value
263 --option1
264 value1
265 --option2
266 value2
267 The configuration file supports comments for human-readable annota‐
269 tions. For example:
270 # company-internal API
272 8.8.8.8/32
273 # home IoT
274 192.168.63.0/24
275
277 Use the following command to route all IPv4 TCP traffic through remote
278 (-r) host example.com (and possibly other traffic too, depending on the
279 selected --method). The 0/0 subnet, short for 0.0.0.0/0, matches all
280 IPv4 addresses. The ::/0 subnet, matching all IPv6 addresses could be
281 added to the example. We also exclude (-x) example.com:22 so that we
282 can establish ssh connections from our local machine to the remote host
283 without them being routed through sshuttle. Excluding the remote host
284 may be necessary on some machines for sshuttle to work properly. Press
285 Ctrl+C to exit. To also route DNS queries through sshuttle, try adding
286 --dns. Add or remove -v options to see more or less information:
287 $ sshuttle -r example.com -x example.com:22 0/0
289 Starting sshuttle proxy (version ...).
291 [local sudo] Password:
292 fw: Starting firewall with Python version 3.9.5
293 fw: ready method name nat.
294 c : IPv6 disabled since it isn't supported by method nat.
295 c : Method: nat
296 c : IPv4: on
297 c : IPv6: off (not available with nat method)
298 c : UDP : off (not available with nat method)
299 c : DNS : off (available)
300 c : User: off (available)
301 c : Subnets to forward through remote host (type, IP, cidr mask width, startPort, endPort):
302 c : (<AddressFamily.AF_INET: 2>, '0.0.0.0', 0, 0, 0)
303 c : Subnets to exclude from forwarding:
304 c : (<AddressFamily.AF_INET: 2>, '...', 32, 22, 22)
305 c : (<AddressFamily.AF_INET: 2>, '127.0.0.1', 32, 0, 0)
306 c : TCP redirector listening on ('127.0.0.1', 12299).
307 c : Starting client with Python version 3.9.5
308 c : Connecting to server...
309 user@example.com's password:
310 s: Starting server with Python version 3.6.8
311 s: latency control setting = True
312 s: auto-nets:False
313 c : Connected to server.
314 fw: setting up.
315 fw: iptables -w -t nat -N sshuttle-12299
316 fw: iptables -w -t nat -F sshuttle-12299
317 ...
318 Accept: 192.168.42.121:60554 -> 77.141.99.22:22.
319 ^C
320 c : Keyboard interrupt: exiting.
321 c : SW'unknown':Mux#1: deleting (1 remain)
322 c : SW#7:192.168.42.121:60554: deleting (0 remain)
323 Connect to a remote server, with automatic hostname and subnet guess‐
325 ing:
326 $ sshuttle -vNHr example.com -x example.com:22
328 Starting sshuttle proxy (version ...).
329 [local sudo] Password:
330 fw: Starting firewall with Python version 3.9.5
331 fw: ready method name nat.
332 c : IPv6 disabled since it isn't supported by method nat.
333 c : Method: nat
334 c : IPv4: on
335 c : IPv6: off (not available with nat method)
336 c : UDP : off (not available with nat method)
337 c : DNS : off (available)
338 c : User: off (available)
339 c : Subnets to forward through remote host (type, IP, cidr mask width, startPort, endPort):
340 c : NOTE: Additional subnets to forward may be added below by --auto-nets.
341 c : Subnets to exclude from forwarding:
342 c : (<AddressFamily.AF_INET: 2>, '...', 32, 22, 22)
343 c : (<AddressFamily.AF_INET: 2>, '127.0.0.1', 32, 0, 0)
344 c : TCP redirector listening on ('127.0.0.1', 12300).
345 c : Starting client with Python version 3.9.5
346 c : Connecting to server...
347 user@example.com's password:
348 s: Starting server with Python version 3.6.8
349 s: latency control setting = True
350 s: auto-nets:True
351 c : Connected to server.
352 c : seed_hosts: []
353 s: available routes:
354 s: 77.141.99.0/24
355 fw: setting up.
356 fw: iptables -w -t nat -N sshuttle-12300
357 fw: iptables -w -t nat -F sshuttle-12300
358 ...
359 c : Accept: 192.168.42.121:60554 -> 77.141.99.22:22.
360 ^C
361 c : Keyboard interrupt: exiting.
362 c : SW'unknown':Mux#1: deleting (1 remain)
363 c : SW#7:192.168.42.121:60554: deleting (0 remain)
364 Run sshuttle with a /etc/sshuttle.conf configuration file:
366 $ sshuttle @/etc/sshuttle.conf
368 Use the options defined in /etc/sshuttle.conf but be more verbose:
370 $ sshuttle @/etc/sshuttle.conf -vvv
372 Override the remote server defined in /etc/sshuttle.conf:
374 $ sshuttle @/etc/sshuttle.conf -r otheruser@test.example.com
376 Example configuration file:
378 192.168.0.0/16
380 --remote
381 user@example.com
382
384 When it starts, sshuttle creates an ssh session to the server specified
385 by the -r option.
386 After connecting to the remote server, sshuttle uploads its (python)
388 source code to the remote end and executes it there. Thus, you don't
389 need to install sshuttle on the remote server, and there are never
390 sshuttle version conflicts between client and server.
391 Unlike most VPNs, sshuttle forwards sessions, not packets. That is, it
393 uses kernel transparent proxying (iptables REDIRECT rules on Linux) to
394 capture outgoing TCP sessions, then creates entirely separate TCP ses‐
395 sions out to the original destination at the other end of the tunnel.
396 Packet-level forwarding (eg. using the tun/tap devices on Linux) seems
398 elegant at first, but it results in several problems, notably the 'tcp
399 over tcp' problem. The tcp protocol depends fundamentally on packets
400 being dropped in order to implement its congestion control algorithm;
401 if you pass tcp packets through a tcp-based tunnel (such as ssh), the
402 inner tcp packets will never be dropped, and so the inner tcp stream's
403 congestion control will be completely broken, and performance will be
404 terrible. Thus, packet-based VPNs (such as IPsec and openvpn) cannot
405 use tcp-based encrypted streams like ssh or ssl, and have to implement
406 their own encryption from scratch, which is very complex and error
407 prone.
408 sshuttle's simplicity comes from the fact that it can safely use the
410 existing ssh encrypted tunnel without incurring a performance penalty.
411 It does this by letting the client-side kernel manage the incoming tcp
412 stream, and the server-side kernel manage the outgoing tcp stream;
413 there is no need for congestion control to be shared between the two
414 separate streams, so a tcp-based tunnel is fine.
415 SEE ALSO:
417 ssh(1), python(1)
418
420 Brian May
421
423 2023, Brian May
4241.1 Jan 21, 2023 SSHUTTLE(1)