Two Services Listening

I posted a question on Friday, and was unable to check news and mail this
weekend. I got a lot of good responses, but I wasn't able to clarify
things.

My question was whether, I can have several services (protocols)
listenening on port 22. Is there anyway to have another service, e.g. http,
listening on the same port, and some sort of director that decides whether
traffic is http or ssh, and forward it to the right service? I have a router
in my home network.

I access my linux box at home from work over 22, which is the only open port
that is common between my ISP and employer. I am well aware of
port-forwarding and use it extensively, and have even gotten ftp to work
with some fiddling.

However, I want to call Harry across town and give him a URL on port 22 to
try, without having ssh, tunnelling, nor an account on my machine.

I hope I clarified my question somewhat.

Someone mentioned setting up a proxy and another mentioned l7 filtering. Do
those still apply? I'll have to do some research on those, since they're a
little above my head at this point.

Buck Turgidson wrote:
> I posted a question on Friday, and was unable to check news and mail this
> weekend. I got a lot of good responses, but I wasn't able to clarify
> things.
>
> My question was whether, I can have several services (protocols)
> listenening on port 22. Is there anyway to have another service, e.g. http,
> listening on the same port, and some sort of director that decides whether
> traffic is http or ssh, and forward it to the right service? I have a router
> in my home network.
>
> I access my linux box at home from work over 22, which is the only open port
> that is common between my ISP and employer. I am well aware of
> port-forwarding and use it extensively, and have even gotten ftp to work
> with some fiddling.
>
> However, I want to call Harry across town and give him a URL on port 22 to
> try, without having ssh, tunnelling, nor an account on my machine.
>
> I hope I clarified my question somewhat.
>
> Someone mentioned setting up a proxy and another mentioned l7 filtering. Do
> those still apply? I'll have to do some research on those, since they're a
> little above my head at this point.


The idea with TCP and UDP ports is to provide two sets of
mailboxes at the destination host. The port numbers are used
to distinguish the service requested, so without some trickery
it's not possible to have several services on one port. You
need to super-multiplex the services on the single port
data stream.

The method to super-multiplex a network segment on a single
port connection is called tunneling. (For the nitpickers: yes,
I know that there are other carriers for tunnels, too).

One possible tunnel tool is OpenVPN which is able to tunnel
an IP subnet or even an Ethernet local net over a single port
connection. However, it needs the tunneling code at both ends
of the connection.

I hope that this clarifies more than messes up.

--

Tauno Voipio
tauno voipio (at) iki fi