SSH config: command for bastion server proxying

Host 51.21.21.11
  IdentityFile ~/.ssh/mykey.pem
  User ec2-user
  ForwardAgent yes

Host 10.*
  ProxyCommand ssh ec2-user@51.21.21.11 nc %h 22
  User ec2-user
  IdentityFile ~/.ssh/mykey.pem
  ForwardAgent yes

Put your ssh public key in ~/.ssh/authorized_keys along the path.

Direct ssh to a server via proxy using putty/plink on Windows

1. Make sure seamless ssh keys are setup to your bastion server for your username
1. Not covered here
2. See: http://www.ualberta.ca/CNS/RESEARCH/LinuxClusters/pka-putty.html
2. Session -> Host Name -> mytargetserver.mydomain.com
3. Connection -> Proxy
1. Proxy Type -> Local
2. Telnet command, or local proxy command 
1. c:/program files (x86)/putty/plink.exe myproxy.mydomain.com -l myusername -agent -nc %host:%port
1. adjust this path to plink.exe to match your local setup
1. hint: install the complete putty install package, not just putty
4. Tunnels
1.   L8081 mytargetserver.mydomain.com:8081

Hint: always hit "Save", no matter what you do, or however inconvenient it was designed to be.

Another example: plink -L 127.0.0.1:1433:mysqlserver.com:1433 admin@google.com -i myprivkeyfile

Taken: http://mikelococo.com/2008/01/multihop-ssh/