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I am working with an AWS environment containing

  • a Ubuntu server to which I can establish an SSH connection
  • a MySQL server
  • an MS SQL server

I can SSH into the Ubuntu server and from there verify connectivity to the MySQL server on port 3306, and the MSSQL server on port 1433 via telnet.

However, if I specify local port forwarding like this in my SSH connection:

 -L 1439:MsSqlIp4Addr:1433 -L 3310:MySqlIp4Addr:3306

From my local machine/client I can verify the connection to the MySQL server via telnet 127.0.0.1 3310. But when I attempt to connect to the MSSQL server via telnet 127.0.0.1 1439, it just hangs for ~100 seconds and then returns "Connection closed by foreign host".

I've tried swapping the local ports to make sure there was no conflict, and I can consistently connect to the MySQL server but not the MSSQL server.

Any ideas?

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  • How do you “test” with telnet? Do you expect a "Connected to..." message or are you waiting for the server's banner (only applies to some protocols)? Commented Feb 8, 2020 at 4:31

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Oddly enough, even though telnet doesn't work, I can still connect to the SQL Server by specifying 127.0.0.1,1439 using standard SQL Server tools.

Don't know why telnet hangs when testing locally but not on the remote machine. I guess that just means it's not a valid test of connectivity.

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