I have computer A, storage server B and HPCC.
Previously, I use A to SSH B and RSYNC files from HPCC to B. One day, B can not PING or SSH or RSYNC or SCP to HPCC. But B can PING or SSH or RSYNC or SCP to A, and A can also communicate with HPCC. So I am trying to use A as a jump host to help B to download files from HPCC.
Got help form https://www.freeture.ch/?p=815.
The first thing is make sure the SSH KEY works between A and B, and between A and HPCC.
In ~/.ssh directory on B, build a new file config. The content is below.