Ports

Start a development server in a machine on port 5173, then open http://127.0.0.1:5173/ in your host browser. nsl forwards the port automatically, usually within a second or so. This works for TCP ports 1024 through 65535, except 5353 and 5355.

How forwarding works

A forwarder runs beside each VM as a user unit. Once a second it asks the VM's agent which TCP ports machines are listening on, and binds each one on host 127.0.0.1:

The machine listens on	The host forwards to
127.0.0.1, 0.0.0.0 or ::	The VM's 127.0.0.1
Only ::1, such as a dev server bound to localhost	The VM's [::1]

Forwarding binds only to host loopback. Other computers on your network can't reach these forwarded ports.

See what is forwarded

nsl ports          # every machine
nsl ports web      # one machine

The output lists the machine for each port. A working forward shows forwarded; a failed one shows conflict and the error.

Conflicts

• A host program already uses the port. The forwarder reports a conflict and retries. It never displaces an existing listener.
• Two machines use the same port. Machines share the VM's network namespace, so the second one cannot listen at all, as in WSL. Give one of them another port.

Outbound traffic

Machines reach the network through the VM's user-mode networking and use the VM's resolver. They have no network configuration of their own.

Isolated machines have their own VM and forwarder, and their ports reach host loopback the same way.