Here’s how to run scp to copy from machine A to machine R, which is only accessible through gateway machine G.
A -G-> R
Set up SSH tunnel:
ssh -L 1234:<address of R known to G>:22 <user at G>@<address of G>
Adding “cat -“ will keep it running while above will get you connected to G:
ssh -L 1234:<address of R known to G>:22 <user at G>@<address of G> cat -
Either way you run it, open another terminal for next step.
Step 2: Run scp against port 1234 pretending 127.0.0.1 (localhost) is the remote machine R, and the command will be sent to R.
scp -P 1234 <user at R>@127.0.0.1:/path/to/file file-name-to-be-copied