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Ping and remote desktop OK ,but telnet fail RRS feed

  • Question

  • I have machine A;

    machine B can ping  and remote desktop to  macine A ;

    but if use "telnet machine A ip port" to connet to machine A ,it show fail;

    but another machine C,use  "telnet machi A ip port" to connect to A ,that work well;

    that mean the machine A service had run well;and i sure both machine have close the firewall

    I wan to to know if I need extra settings on machineB ?
    Thank you for your response;


    • Edited by Fent1982 Friday, May 29, 2020 8:17 AM
    Friday, May 29, 2020 8:15 AM

All replies

  • Configure the firewall on both machines to log dropped packets.

    https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-firewall/configure-the-windows-firewall-log

    To test connectivity, use Powershell instead of telnet.

    Test-NetConnection -ComputerName machineA -CommonTCPPort RDP
    Test-NetConnection -ComputerName machineA -CommonTCPPort SMB
    Test-NetConnection -ComputerName machineA -Port *the*port*number*
    

     Review the C:\Windows\System32\LogFiles\Firewall\pfirewall.log   file for dropped packets. 

    Friday, May 29, 2020 1:04 PM
  • Use Telnet to Isolate the Cause
    One more thing you need to try is to Telnet to port 3389 and see if you're actually able to make a connection. On your local PC run the command:

    telnet remote_pc_or_ip 3389
    Note: You may need to turn on the "Telnet Client" Windows feature in order to enable this command.

    If you are immediately taken to a completely blank screen, the connection was successful. If necessary press Ctrl+] followed by quit then Enter to exit the telnet session.

    However, if you get any other response, (e.g. "Connection Refused") then it's clear something is blocking your traffic. You need to find out what that is and disable it.

    It may be helpful to try to connect using the remote PC's NetBIOS name, DNS hostname, and IP address. Sometimes an improperly configured network can lead to one form working while others don't. You may even wish to try the target machine's IPv6 address.

    Additionally you can run Telnet directly on the computer you're trying to connect to in order to confirm it's properly configured to accept RDP connections:

    telnet 127.0.0.1 3389
    This has the advantage of testing the RDP connection without going through any firewalls or security devices that may be filtering network traffic. Even most locally installed security programs will allow locally initiated network traffic when they're otherwise blocking traffic from remote nodes.

    If this test succeeds, but connections from remote machines fail, then you can be certain hosted Virtual Desktop services are working correctly, but something is indeed blocking network traffic between the remote and local PCs.
    Friday, May 29, 2020 2:55 PM