Telnet Connection Fails - How exactly does Telnet open communication ports?

SFrushon

Honorable
Nov 24, 2013
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10,510
This seems like a simple basic question and in need of a simple basic answer. I'm a bit rusty with this old networking TELNET command. I am using it as a test of connectivity from a Win 7 workstation to an internet mail server via port 110. We have a dozen identical new PC's, and this one in particular was purchased after the first few and the only one that fails to connect.

Question 1: Does Telnet open port 110 on he remote mail server to connect?
Question 2: What port on the local workstation is used / opened to communicate?
Question 3: What are the possible causes of Connection Failure?

Like I said, I'm a bit rusty with this basic networking test. Can someone please help explain the process of this connection test - eg, is the mail server listening to it's port 110 and waiting for a connection request? How does the mail server respond and make the connection successful? What does the workstation have to do to insure that the connection is successful? What port does the workstation use to connect?

No windows firewall, no antivirus or network security is enabled. We sit behind a netgear router and use private ip on our local domain workstations. Comcast assigns the internet IP addresses. Network Solutions should allow communication on the mail port from any ip, right?

We have tried DELL, Comcast, NetSol, Microsoft, 3rd party tech and have been trying to solve this dilemma since April 2013. The only thing we did not try is a new nic card or complete re-install of Win7, because it seems extreme since this communication issue is the only problem.

PLEASE HELP.

Regards,
sf
 
Solution
The key on wireshark is to see if the session opens and how far it gets.

You should see syn client send syn, server send syn-ack, client send ack. These 3 messages indicate that communication is working in both directions. Key will be which if any is missing. Generally when it does not work you see the client send syn over and over. If this happens it means the PC is not really sending the syn or somthing is blocking it.

If you get a full handshake then you need to watch the pop messages to see what it does. If you are running pop3 sometime it will net get a secure session open because of key or certificate issues. Best bet is to run a wireshark on a machine that works and compare it to this one to see what is different.
I will assume you mean you are telneting to port 110. Pretty much all that you can verify with telnet is the 3 way handshake of the TCP session setup.

You will need to run a real POP mail client to see what is going on. Get a copy of wireshark and see what it tells you . Wireshark will decode the pop messages so if you are getting a reject from the server you will be able to tell why.
 

SFrushon

Honorable
Nov 24, 2013
4
0
10,510
Yes, port 110 for this POP3 mail server, all we want to confirm is a successful connection.
I now have wire-shark installed and running, a bit complex...memory of the past.

What should I try next and look for?
Thank You Bill.

We can ping and tracert the servers locally. We can access the internet and access webmail via internet. Can send/receive via internet webmail site. Can send mail locally via Outlook.

We cannot receive email locally via Outlook 2010 because this pc will not communicate with the internet mail server on port 110: cannot telnet successfully. It is odd that we can telnet the smtp server successfully via port 25 on this pc, but cannot on port 2525. Port 2525 is the required port to send emails via outlook. All other identical pc's are successful with all telnets.
 
The key on wireshark is to see if the session opens and how far it gets.

You should see syn client send syn, server send syn-ack, client send ack. These 3 messages indicate that communication is working in both directions. Key will be which if any is missing. Generally when it does not work you see the client send syn over and over. If this happens it means the PC is not really sending the syn or somthing is blocking it.

If you get a full handshake then you need to watch the pop messages to see what it does. If you are running pop3 sometime it will net get a secure session open because of key or certificate issues. Best bet is to run a wireshark on a machine that works and compare it to this one to see what is different.
 
Solution