Interactive OpenSSH ~/.ssh/config File Builderv7.3+ ProxyJump
Build multi-host OpenSSH client configuration files with ProxyJump bastion hosts, IdentityFile keys, port forwarding, and keepalive settings. 100% computed on your client device with zero server telemetry.
Host Inventory & Parameters
(3 configured)Name you type into terminal: ssh bastion
Real domain name or IPv4/IPv6 server address.
Remote login username.
SSH listening port (Default: 22).
Installation & Terminal Quick Start
OpenSSH will strictly ignore config files and keys that have loose permissions. Run:chmod 700 ~/.ssh && chmod 600 ~/.ssh/config ~/.ssh/id_*
Essential OpenSSH Configuration Reference & Best Practices
Architectural reference guide for building high-reliability, hardened OpenSSH client configurations.
ProxyJump vs ProxyCommand
Introduced in OpenSSH 7.3, ProxyJump bastion replaces the old ProxyCommand ssh -W %h:%p bastion. It allows chaining multiple jump nodes (e.g. jump1,jump2) while preserving end-to-end cryptographic encryption between your local terminal and target host.
IdentitiesOnly yes
When your local ssh-agent holds multiple SSH keys, the client will iteratively offer every key to the remote server. Many hardened servers disconnect after 5 failed key attempts with Too many authentication failures. Enabling IdentitiesOnly yes restricts authentication to only the specified key.
ControlMaster Multiplexing
SSH connection establishment requires TCP three-way handshake, TLS key exchange, and authentication negotiation (500ms–2000ms). Multiplexing creates a local Unix socket (ControlPath) so subsequent SSH sessions, rsync jobs, and git pushes reuse the existing connection in under 20ms.
Tunneling Modes Cheat Sheet
- LocalForward (-L): Binds your local port and forwards traffic to remote destination. Ideal for private RDS database access.
- RemoteForward (-R): Exposes a service running on your local machine to the remote server.
- DynamicForward (-D): Creates a local SOCKS5 proxy to route web browser requests through the remote machine.
StrictHostKeyChecking accept-new
Setting StrictHostKeyChecking no completely bypasses MITM verification. The modern setting accept-new automatically registers unseen host keys into ~/.ssh/known_hosts without prompting, but immediately terminates the connection if a previously known host key changes unexpectedly.
Keepalive & Timeout Settings
Stateful firewalls and NAT gateways drop idle TCP sessions after 60–120 seconds. Configuring ServerAliveInterval 60 and ServerAliveCountMax 3 guarantees the client transmits encrypted null packets through the tunnel every minute, keeping the session alive indefinitely.