SSH directly to a box behind a jumpbox aka bastion host - useful for sshing to EC2 instances in private subnets

SSH leapfrog

#
# Latest in Gist: https://gist.github.com/colinangel/b85d0e1fb9b6a2d4f66a
#
# NOTE: This uses ProxyCommand instead of ssh-agent because it's insecure.
# Replace 172.31.1.x with the IPs in your subnet
# Also replace the two IdentityFiles with your ssh key(s)

# Jumpbox
Host jmp 
  Hostname 172.31.1.10
  User jumpbox-user
  IdentityFile ~/.ssh/jumpbox-key.pem

# Automatically use jumpbox to connect to any ip address in the range specified
# e.g. ssh [email protected]
Host 172.31.1.*
  ProxyCommand ssh ec2-user@jmp -W %h:%p
  User ec2-user
  IdentityFile ~/.ssh/destination-key.pem
  # since new instances reuse old IPs, skip host key checking
  StrictHostKeyChecking no
  UserKnownHostsFile=/dev/null

# Multiplex connections so we don't have to open so many
# faster connections, and ability to use local editors on remote boxes
Host *
  ControlMaster auto
  ControlPath ~/.ssh/master-%r@%h:%p
  ControlPersist 1h
  # keep connections despite network hiccups for up to 15 minutes
  TCPKeepAlive no
  ServerAliveInterval 60
  ServerAliveCountMax 15