Proxy (Jump Host) & Resolving SSH Known Host Errors

A well-configured ~/.ssh/config file can cleanly resolve most SSH connection problems.

Configuration example

# opc_mx → server accessed through the bastion
Host opc_mx
  HostName server_~~~
  User opc


# ============================
# Proxy server & defaults
# ============================

# BASTION: jump host (external access gateway)
Host BASTION
  HostName IP_ADDRESS
  User opc
  Port 9129391239
  IdentityFile ~/.ssh/id_ed25519


# Hosts matching proxy_* and opc_*: connect through the bastion
Host proxy_* opc_*
  # Improve connection speed through session sharing when matching multiple hosts
  ControlMaster auto
  ControlPath ~/.ssh/%r@%h:%p

  IdentityFile ~/.ssh/id_ed25519

  # Use the bastion as a jump host
  ProxyCommand ssh -W %h:%p BASTION


# Defaults (applied to all hosts)
Host *
  UseKeychain yes
  # Disable StrictHostKeyChecking: ignore known host warnings
  StrictHostKeyChecking no
  AddKeysToAgent yes
  IdentityFile ~/.ssh/id_ed25519

Key configuration settings

Setting	Description
ControlMaster auto	Reuse an existing session for multiple SSH connections to the same host
ControlPath	Socket file path used for session sharing
ProxyCommand	Tunnel configuration through a jump host
StrictHostKeyChecking no	Skip the known_hosts check on the first connection (convenience)
UseKeychain yes	Store the passphrase in the macOS Keychain