Bypassing jump server

SSH jump hosts are employed as an alternative to SSH tunneling to access internal machines through a gateway.

The idea is to use ProxyCommand to automatically execute the ssh command on remote host to jump to the next host and forward all traffic through.

Jump through CLI:

user$ ssh -J user1@host1:port1 user2@host2 -p port2

Using config:

1.Single jump

ProxyJump hosts can be defined inside each user’s SSH config file.

Eddit — — -> ~/.ssh/config

### First jump host. Directly reachable
Host betajump
  HostName jumphost1.example.org
 
### Host to jump to via jumphost1.example.org
Host behindbeta
  HostName behindbeta.example.org
  ProxyJump  betajump

2.multiple jump

The same syntax can be used to make jumps over multiple machines:

Eddit — -> ~/.ssh/config

### First jump host. Directly reachable
Host alphajump
  HostName jumphost1.example.org
 
### Second jumphost. Only reachable via jumphost1.example.org
Host betajump
  HostName jumphost2.example.org
  ProxyJump alphajump
 
### Host only reachable via alphajump and betajump
Host behindalphabeta
  HostName behindalphabeta.example.org
  ProxyJump betajump

user$ ssh behindalphabeta

It works with scp too:

user$ scp filename behindalphabeta:~/