[X-Unix] Port Forwarding ssh using -R option

[Daniel Morrison]

The -R is to forward from a port on one machine to another machine.  But
it won't work unless you can SSH to your router from your Mac.

So, if I had my Mac, a Linux gateway, and an outside client machine, it 
might go something like this:

1) I ssh from my Mac to the gateway, telling it to redirect any connection 
to port 1025 on gateway to port 22 on the mac.

2) I keep this connection open, as the port forwarding tunnels through 
this secure connection.

3) When, from the client machine (or any other machine), I ssh to port 
1025 on gateway, it is forwarded to port 22 on the Mac and I connect.  
Note that I could do the same thing with http and port 80, etc.

>From the man page:

        Specifies that the given port on the remote (server) host is to
        be forwarded to the given host and port on the local side.  This
        works by allocating a socket to listen to port on the remote
        side, and whenever a connection is made to this port, the connec­
        tion is forwarded over the secure channel, and a connection is
        made to host port hostport from the local machine.  Port forward­
        ings can also be specified in the configuration file.  Privileged
        ports can be forwarded only when logging in as root on the remote
        machine.

So, unless you can SSH to the router, this won't work.  However, ussually 
broadband routers have a setting that allows forwarding of a port at the 
router to a port on an internal machine.  So you should be able to forward 
router port 22 to Mac port 22 using that, if your router supports it.

Good Luck, 
Dan

On Thu, 5 Feb 2004, Our Pal Al wrote:

> At least I think the -R option is what I want.
> 
> I've already got my home Mac listening to ssh on 22 as normal but moved it
> behind a wireless router last night (doing ddns so I can still always reach
> it from outside) and want to be able to ssh into my mac and my Xandros linux
> box at will. I want to map port 22 on the router to the linux box and then
> change the mac to listen to another port and I'll append that port # when I
> ssh to it. 
> 
> Or maybe I'll do it the other way around once I figure out how to get ssh to
> listen on another port. Once I've got the right syntax down I should be able
> to change either but I can't get -R to work. Or is this even really the
> option I want? How can I get ssh to listen on another port? Right now I hop
> from the mac to the linux box but I'd like to eliminate a second step in
> getting to either.
> 
> - opa
> 
> 
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-- 
Dan Morrison                                             http://www.eagle7.org
dmorriso at eagle7.org                                               AIM: EaglVII