156

Well, referring back to this question, I am running the command

ssh -R 8080:localhost:80 -N root@example.com

on a Mac. Yet the port that is being tunneled is not working publicly. I am running such a command to make it so that the local port can be opened on the remote computer. And it does work when opening the port on localhost on the remote computer, but when I try to access the public IP address of the remote computer from my local computer the port doesn’t seem to be open. How would I make the tunnel public on the IP for anyone to access?

EDIT: It seems as if the remote side binds only on localhost instead of to all interfaces.

EDIT 2: The client is Mac OS X 10.6 and the server is Linux Mint, but they’re both OpenSSH.

  • What does public IP mean? If you are trying to connect to a local computer thru the router and via the Internet, most routers will not allow such loopback. – harrymc Apr 30 '13 at 5:53
320
+50

If you check the man page for ssh, you'll find that the syntax for -R reads:

-R [bind_address:]port:host:hostport

When bind_address is omitted (as in your example), the port is bound on the loopback interface only. In order to make it bind to all interfaces, use

ssh -R \*:8080:localhost:80 -N root@example.com

or

ssh -R 0.0.0.0:8080:localhost:80 -N root@example.com

or

ssh -R "[::]:8080:localhost:80" -N root@example.com

The first version binds to all interfaces individually. The second version creates a general IPv4-only bind, which means that the port is accessible on all interfaces via IPv4. The third version is probably technically equivalent to the first, but again it creates only a single bind to ::, which means that the port is accessible via IPv6 natively and via IPv4 through IPv4-mapped IPv6 addresses (doesn't work on Windows, OpenBSD).  (You need the quotes because [::] could be interpreted as a glob otherwise.)

Note that if you use OpenSSH sshd server, the server's GatewayPorts option needs to be enabled (set to yes or clientspecified) for this to work (check file /etc/ssh/sshd_config on the server). Otherwise (default value for this option is no), the server will always force the port to be bound on the loopback interface only.

  • 10
    OH MY GOD IT WORKED!!!!! I have done exactly that 1 million times!! I just forgot that * in bash will give files and i needed \* – Trevor Rudolph May 6 '13 at 7:08
  • 3
    Yeah, that's exactly why I always prefer 0.0.0.0 - it's IPv4 only, but it'll do most of the time :) – Stefan Seidel May 6 '13 at 7:51
  • 24
    GatewayPorts yes solved my problem. – Sunry Oct 25 '16 at 8:18
  • 4
    GatewayPorts = yes (on the remote sshd config) fixed it for me too – Phil_1984_ Dec 5 '16 at 13:29
  • 3
    "GatewayPorts yes" made my day, thanks @StefanSeidel – karser Oct 27 '17 at 10:40
36

Edit:

-g works for local forwarded ports, but what you want is a reverse/remote forwarded port, which is different.

What you want is this.

Essentially, on example.com, set GatewayPorts=clientspecified in /etc/ssh/sshd_config.

--- previous (incorrect) answer ---

Use the -g option. From ssh's man page:

-g     Allows remote hosts to connect to local forwarded ports.
  • doesn't seem to be working... it starts up but i cant connect remotely – Trevor Rudolph Apr 28 '13 at 6:21
  • 1
    Try running netstat -elnpt from a separate tty to figure out what ports are bound to what address. Without -g, a port should be bound to 127.0.0.1:PORT. With -g, it should be bound to 0.0.0.0:PORT, which makes it accessible remotely. – snapshoe Apr 28 '13 at 14:58
  • pastebin.com/q6f4kJyd – Trevor Rudolph Apr 28 '13 at 16:11
  • 1
    GatewayPorts=clientspecified or GatewayPorts clientspecified – Trevor Rudolph Apr 29 '13 at 0:01
  • and do i add that to the client or remote? – Trevor Rudolph Apr 29 '13 at 0:04
11

Here's my answer for completion:

I ended up using ssh -R ... for tunneling, and using socat on top of that for redirecting network traffic to 127.0.0.1:

tunnel binded to 127.0.0.1: ssh -R mitm:9999:<my.ip>:8084 me@mitm

socat: mitm$ socat TCP-LISTEN:9090,fork TCP:127.0.0.1:9999

Other option is to do a local-only tunnel on top of that, but i find this much slower

mitm$ ssh -L<mitm.ip.address>:9090:localhost:9999 localhost

  • I like the fact that I don't have to deal with the sshd configuration and that I can do all of it without sudo. Plus I learn that socat exists. Thanks! – BrutusCat Jun 12 '14 at 14:00
9

You can also use a double forward if you won´t or can change /etc/ssh/sshd_config.

First forward to temporary port (e.g. 10080) on loopback device on the remote machine, then use local forward there to redirect port 10080 to 80 on all interfaces:

ssh -A -R 10080:localhost_or_machine_from:80 user@remote.tld "ssh -g -N -L 80:localhost:10080 localhost"
  • 1
    This actually works to bypass forwarding rules! – Michael Schubert Dec 3 '16 at 18:49
  • Love this solution. Great workaround when you don't want the change the config on the machine – Grezzo Aug 18 '17 at 14:54
8

Use the "gateway ports" option.

ssh -g -R REMOTE_PORT:HOST:PORT ...

In order to use that, you probably need to add "GatewayPorts yes" to your server's /etc/ssh/sshd_config.

  • Actually this worked. What I do is that I use an EC2 instance as a forwarder to my REST server. This way, I don't need to stick my server in the DMZ and I don't need a public IP. Funny enough, with the first EC2 instance I created, ssh -R remote_port:localhost:port xxx@ec2xxx worked just fine but then I had to create another instance later on for some reason and from that point on, I was always getting: connection refused. Used tcpdump to look at what I was getting and there wasn't much info. -g plus GatewayPorts yes did the trick. – E.T Jan 24 '17 at 19:12
0

If you'd like to put the configuration in you ~/.ssh/config instead of using command line parameters, you can try something like

Host REMOTE_HOST_NAME RemoteForward \*:8080 127.0.0.1:80

Remember to have you remote host's firewall allow connections to 8080 and ensure that the GatewayPorts option of your /etc/ssh/sshd config isnt set to no

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