Re: Change telnet to another port? -- MIDRANGE-L

John,

The way a lot of routers work is you telnet to them to configure them,
using the standard port of 23.  I know Cisco and Motorola routers
work this way, as apparently this DSL router does.  Normally, this
wouldn't be a problem, as it is the port on the router, and not for the
machines.

Some xDSL routers, however, are also proxy servers it seem.  Your
machines use a local network IP address scheme (such as 192.168.x.x)
which the router listens to and forwards to the internet.

Proxy servers, however, are usually used as origin only, and not on
the receiving side.  That is, I can connect to a remote site from my local
network, but remote sites can't get to me.  Which is why it's a firewall.
To get around this, you have the port mapping you are talking about,
a remote site starts a connection to the router on a port, which then
gets forwarded into my local area network, to a specific IP address.
Port 80 goes to the IP of my web server, port 110 goes to the IP of
my POP3 server, port 25 goes to the IP of my SMTP server, etc...

The problem in this case is that the router itself has to listen to port 23
for configuration log in.  So that "they" aren't mapping port 23 to any
other IP address.  What would happen if they did route port 23 to the IP
of the AS/400?  And the router had to be configured?  How would they
configure it?

With Cisco and Motorola Routers it is a simple matter of plugging into
the devices built in COM port and configuring it that way.  I don't think
that is an option with DSL routers that contain proxy servers.

The best solution (if not the only one) is get rid of the DSL router that's
a proxy server and replace it with a simple DSL router.  Then build a
proxy server behind it.  What this would do would be to give you 2 IP
addresses you could telnet to port 23 to.  The IP of the router, and the
IP of your proxy server (which would be the only public IP addresses
in your LAN).

Regards,

Jim Langston

John Hall wrote:

> It just doesn't work that way.  Someone somewhere along the line has got
> something wrong.
>
> you cannot "use" a port up on a network.  We probably have 20 or 30
> devices that are managed through telnet (port 23).  Including a router
> that is managed by the ISP.  There is no reason to change the settings
> on the 400 because of how a router is managed.  a port is not used to
> route traffic across the network.  It is used to help the computers at
> each end determine how to handle the traffic.  It can also be used to
> block certain types of info at a firewall / proxy server (we have
> both).  The port #'s used are by convention only.  You can run a web
> server on port 23 and telnet on port 80 if both systems are setup that
> way.
>
> If you ISP insists telnet cannot use the standard ports tell that they
> lack sufficient knowledge to set it up correctly.  Tell them you are
> going to call IBM support line at $$$ per hour to reconfigure your as400
> and they will have to pay for it.
>
> You might be suprised how quickly the impossible becomes the possible !
>
> John Hall
> Home Sales

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