A jump host, sometimes called a bastion, is a server you connect through to reach machines that are not reachable from your workstation. It is the usual pattern for production estates where the only way in is a single hardened entry point.
How Luumen Handles It
Luumen connects in two stages. It authenticates to the jump host with the jump host's own credential, then opens the connection to the target using the target's credential. The two do not share authentication, so a restricted jump host account works alongside a more privileged account on the target. While connecting, the progress view shows the hop through the jump host as its own step, and a failure names which stage failed.
Luumen supports one hop. Each target connects through a single jump host, and a jump host cannot itself have one. If you need a chain of two or more, configure it in your own ~/.ssh/config with ProxyJump and connect to the final target directly.
Mark a Host as a Jump Host
On the Hosts page, select the hamburger menu for an individual host, then select Edit.
On the Edit Host page, toggle Mark as Jump Host, then Save.
Ensure you have a credential attached. This is what Luumen uses for the first hop.
Routing a Host Connection Through a Jump Host
Now that you've created a Jump Host, you can use it as a connection gateway for one or many of the other hosts you've created.
Select the Host you want to route through the jump host, click the three dots beside Connect"..." then select Edit.
Choose the jump host from the Connect via field, then select Save.
Practical Advice
Use a dedicated account on the jump host, so its activity is easy to distinguish when reviewing access.
Test the jump host on its own first. If it cannot connect, everything behind it fails the same way, and the error can look like a problem with the target.
A Windows Host cannot be a jump host, and cannot be reached through one.