1

I've got dropbear v2019.78 running on a custom embedded linux 2.6.28.10, on an ARM9

And, I'm trying to setup local port forwarding from my Ubuntu 16.04 desktop (using telnet just for testing):

ssh -g -N -l root -L 2222:myarm9.com:23 [email protected] -vvv

Output of the port forwarding bits:

debug1: Local connections to *:2222 forwarded to remote address myarm9.com:23
debug3: channel_setup_fwd_listener_tcpip: type 2 wildcard 1 addr NULL
debug1: Local forwarding listening on 0.0.0.0 port 2222.
debug2: fd 5 setting O_NONBLOCK
debug3: fd 5 is O_NONBLOCK
debug1: channel 0: new [port listener]
debug3: sock_set_v6only: set socket 6 IPV6_V6ONLY
debug1: Local forwarding listening on :: port 2222.
debug2: fd 6 setting O_NONBLOCK
debug3: fd 6 is O_NONBLOCK
debug1: channel 1: new [port listener]
debug2: fd 4 setting TCP_NODELAY
debug3: ssh_packet_set_tos: set IP_TOS 0x10
debug1: Entering interactive session.
debug1: pledge: network

Then, when trying telnet localhost 2222:

debug1: Connection to port 2222 forwarding to myarm9.com port 23 requested.
debug2: fd 7 setting TCP_NODELAY
debug2: fd 7 setting O_NONBLOCK
debug3: fd 7 is O_NONBLOCK
debug1: channel 2: new [direct-tcpip]
debug3: send packet: type 90
debug3: receive packet: type 92
channel 2: open failed: connect failed:
debug2: channel 2: zombie
debug2: channel 2: garbage collecting
debug1: channel 2: free: direct-tcpip: listening port 2222 for myarm9.com port 23, connect from ::1 port 50874 to ::1 port 2222, nchannels 3
debug3: channel 2: status: The following connections are open:

Output from telnet, which says nothing much:

 $ telnet localhost 2222
Trying ::1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.

I don't see any interesting output from dropbear itself.

Any ideas on how to debug? Dropbear works OK when using a newer embedded system, running on an Armv7, but on this particular system it's giving me trouble. I've also tried using ssh from a WSL prompt from a Windows machine (exact same story), and also tride putty as a client (lots of output, not sure what's relevant, but still doesn't work)

Improve this question
4
  • 1
    Does myarm9.com know it is myarm9.com itself? Usually you use like -L 2222:localhost:23 or -L 2222:127.0.0.1:23. Is there a process that listens on the port 23 on the server? On which interface does the process listen?
    – Kamil Maciorowski
    Commented Jun 8, 2020 at 12:25
  • Hi @KamilMaciorowski not sure what you mean on myarm9.com, that's the hostname on that emb. Linux. About the options, my idea for testing this is to connect remotely to that SSH server and setup local port forwarding, so when I try to connect to a port in my desktop PC, I'm forwarded and connecting to a port in myarm9.com. Port 23 is telnet.
    – ArthurChamz
    Commented Jun 8, 2020 at 12:31
  • 1
    (1) Any computer resolves myarm9.com by itself. With ssh -L 11:foo:99 it's the server who resolves foo. It's possible the machine with the SSH server resolves myarm9.com differently or not at all. Therefore I'm asking if it knows it's myarm9.com itself. Systems usually know they are localhost. They should always know they are 127.0.0.1. (2) I know 23 is assigned to telnet (protocol). But it's not a crime to have another server on this port or no server at all. I'm asking if there's a process (e.g. telnet server) actually listening.
    – Kamil Maciorowski
    Commented Jun 8, 2020 at 12:42
  • Hi @KamilMaciorowski (1) that was it! Thanks for explaining it's the SSH server who resolves myarm9.com I changed it to 127.0.0.1 and it works as expected, thanks again :)
    – ArthurChamz
    Commented Jun 8, 2020 at 13:47

0

Reset to default

You must log in to answer this question.

Browse other questions tagged .