[SOLVED] Unable to Make a Remote Telnet Connection to JLink GDBServer

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  • [SOLVED] Unable to Make a Remote Telnet Connection to JLink GDBServer

    I am having issue making remote telnet connection to JLink GDBServer in order to receive RTT data. Specifics:

    Raspberry Pi/Ubuntu Server 20.04
    • Development station running gdb-multiarch V12.0.90


    PC/Windows 10
    • Running JLink GDBServer V7.70
    • USB Connection to a Nordic nRF52840 development board
    Problem Description
    • I am able to debug programs across the remote connection, as I have unchecked the JLink GDBServer Localhost only checkbox.
    • I can connect to the JLink GDBServer telnet port on the Windows side using RTT Viewer, PuTTY and the Windows telnet utility.
    • I cannot connect to the JLink GDBServer telnet port from the Raspberry Pi using the Linux telnet utility. I get a connection refused error.
    • I have worked with the Windows firewall to allow all incoming connections during these tests. This was not necessary to do debugging though.



    I'm at a bit of a loss as to what might be going on. Is the JLink GDBServer program prepared to accept remote connections to the telnet output port?
  • I was able to work around the issue by creating a port forwarding rule on the Windows PC:

    netsh interface portproxy add v4tov4 listenport=19020 connectaddress=127.0.0.1 connectport=19021

    My remote connection connects to port 19020 on the PC where GDB Server is running and is forwarded to 19021. Telnet data now flows freely from GDB Server to my Linux telnet client.

    My conclusion at this point is that GDB Server is not accepting remote connections on the telnet port for some reason. GDB Server won't accept remote connections for debugging unless specifically enabled.

    SEGGER Team,
    Is the behavior described accurate and intentional?
  • Hi,

    I am confused.
    Are you talking about one of these GDB Server listening ports?


    Or are you talking about this one?:
    wiki.segger.com/RTT#TELNET_channel_of_J-Link_software
    Please read the forum rules before posting.

    Keep in mind, this is *not* a support forum.
    Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
    Should you be entitled to support you can contact us via our support system: segger.com/ticket/

    Or you can contact us via e-mail.
  • Update:
    The RTT TELNET port was indeed only available for localhost, even when Localhost only was not selected.
    This will be fixed with the next J-Link version (V7.80c) planned for the 27th of September.

    BR
    Fabian
    Please read the forum rules before posting.

    Keep in mind, this is *not* a support forum.
    Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
    Should you be entitled to support you can contact us via our support system: segger.com/ticket/

    Or you can contact us via e-mail.