Use case
An engineer needs a shell on one remote server — not standing network membership that happens to include SSH reachability.
A private overlay network grants IP-level reachability to every device on it; SSH is then just one of many things that happens to be reachable. That is more connectivity than an SSH-only need requires.
The TunnelCrib Agent on the target server advertises its ssh Service (port 22 by default). The requesting Client is authorized for that Device and Service only.
$ tunnelcrib connect prod-web-01:ssh
device identity verified
direct Tunnel negotiated
Service Tunnel active
localhost:49318
$ ssh -p 49318 user@localhost
Access is scoped per Client, per Device, per Service — an engineer authorized for SSH on one server is not automatically authorized for SSH (or any other Service) on any other Device.
The engineer's normal SSH client and credentials/keys are used against localhost:<port>; TunnelCrib carries the TCP connection but does not participate in the SSH session's own authentication.
Connect and session-close events are recorded (see audit events).
TunnelCrib's own Device-identity and per-session key pinning (see transport) authenticate the Tunnel itself; the SSH session inside it still uses its own independent authentication.