telnet on local LAN question

[Paul Allen Newell]

On 8/17/2011 10:42 PM, Andre Speelmans wrote:
>>> An additional thing to check is if you are listening on port 23 (or 25).
>>> Try "netstat -tnlp" and search ":23" (or ":25"). You will find the
>>> name of the process listening. Check if it is listening on 0:0:0.0 or
>>> just on 127.0.0.1. The 127.0.0.1 would be wrong, and should be fixed
>>> in the configuration of the mail program.
>> I have an entry for :25 ... 127.0.0.1:25. No entry for :23.
> You just pinpointed why you can not telnet (port 23) or reach port 25.
>
> The mailserver is only listening on localhost (127.0.0.1) and can't be
> reached from other machines. And there is no telnet-daemon running, so
> nothing will answer on that port either. (Also, as said in my previous
> post: your firewall still does not allow port 25 connections.)
>
>> Given that I am using telnet and not mail as it seems like a simplier
>> problem to learn how to get commands/ports to work on my LAN (mail seems
>> to have multiple ports and telnet is a single one ... and a very simple
>> test to run), what do I need to do if 127.0.0.1 is wrong for telnet
>> 23/25 or telnet without a specified port (which seems to be 23, right?)
> Mail can be used on port 25 nicely, you just have to configure it to
> listen on all interfaces. (Not sure what line is needed from the top
> of my head.)
>
> If you want to try it on telnet then you need a telnet-server
> installed and running.
> But why would you do that? If you can ssh/ping to the machines, you
> have demonstrated they can reach each other finely and there is no
> need for any telnet server, as that won't tell you anything you didn't
> already know. You want to mail, so get your mailserver running on all
> interfaces and open your firewall for port 25. Or, during tests drop
> it altogether, until you know you can mail.
>
Andre:

Once again, thanks for replies (I still have to go through the other 
one) and appreciate understanding my 24 hour delay.

I am afraid I do not understand this as I can use telnet.

Part of trying to get mail / mailx running on my Linux boxes to send 
mail to pnewell at cs.cmu.edu involved using telnet as a test. They wanted 
me to use port 587 per their online docs. To get mail to work, I had to 
edit sendmail.mc to understand port 587.

So, I can type:
+++
telnet MX-LB--1.SRV.cs.cmu.edu 587
+++

and it works. I presume that I don't have to edit anything to let telnet 
know about 587 is that its their end that is going to determine whether 
they will accept the telnet and they are listening on 587.

Yes, I did try telnet <name> 587 to confirm that it doesn't work as my 
boxes know nothing about 587 above and beyond the config in sendmail.mc 
for mail / mailx.

I can also telnet <name> 22 and see that it hooks up to port 22 (ssh), 
though it is utterly useless.

Why would I need to install a telnet server ... unless I was trying to 
do a network properly and wanted to have mail server, file server, 
whatever server. Not the this isn't the right thing to do, but it 
doesn't seem to solve the problem of "what is blocking my request from 
one machine to another?"

If I am missing something, I will welcome the enlightenment.

Thanks,
Paul