From: Brian Candler <b.candler@...>
Date: 2011-05-27T20:11:31+09:00
Subject: Re: Net::Telnet into Net::SSH

Josh Hurtado wrote in post #1001108:
>  Does anyone know if there is way to run a NET::TELNET object in a
> NET::SSH session?
>
> I have a secure jump server that I want to have ruby ssh into then run a
> group of NET::Telnet object. For grabbing running-config from Cisco
> routers.

The question doesn't really make much sense in its current form, but the 
following might help.

(1) If you want to use Net::SSH but with a Net::Telnet-style API, then 
look at Net::SSH::Telnet (separate package)

(2) If you are ssh'ing to a box, then via the command line you can issue 
the command "telnet x.x.x.x". At that point, anything you send to the 
remote host (over ssh) will be relayed to x.x.x.x (over telnet)

This does not involve Net::Telnet at all.

(3) A cleaner way is to use ssh port forwarding: open an ssh connection 
to the intermediate host, but set up LocalForward from port yyy to 
x.x.x.x port 23. Then you can telnet to 127.0.0.1 port yyy

You can demonstrate this at the command line:

ssh -L 1234:x.x.x.x:23 my-ssh-host

(in another window)
telnet 127.0.0.1 1234

And you can do the same using Net::SSH - there is an example in 
README.rdoc

    # forward connections on local port 1234 to port 80 of 
www.capify.org
    ssh.forward.local(1234, "www.capify.org", 80)
    ssh.loop { true }

If you do this, then you can use Net::Telnet to open a connection to 
127.0.0.1 port 1234, and it will be transparently proxied through to the 
end target. This sounds to me closest to what you're trying to achieve.

This depends on the ssh host supporting port forwarding. Most of them 
do, but some don't (e.g. Cisco routers ssh don't)

(4) You can also use the command line ssh with dynamic SOCKS 
port-forwarding; a single ssh connection can then be used to tunnel 
connections to multiple routers, without having to assign a different 
local port for each. But AFAIK, Net::SSH doesn't support this. If you 
spawn the command-line ssh you can use this. You'd need to get 
Net::Telnet to work via a SOCKS proxy too.

If you're doing this in Ruby, assigning a new local port for each 
forwarded connection will probably be easier.

HTH,

Brian.

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