Modem mode and router mode: what changes, and why your settings page moves
Modem mode switches off your hub's router, Wi-Fi and firewall, and hands the connection straight to equipment of your own. On some makes it also moves the hub's settings page to a different address, which is the single most common reason a hub suddenly appears unreachable.
What actually changes
In its normal state your hub does several jobs at once: it terminates the broadband connection, hands out addresses to your devices, runs the firewall and broadcasts the Wi-Fi. In modem mode it stops doing all but the first. It becomes a bridge, and everything else becomes your router's responsibility.
Usually only one of the hub's Ethernet ports stays active, and that is where your own router plugs in. The Wi-Fi goes silent, which is expected rather than a fault.
Why the settings address moves
Once the hub is no longer routing, it no longer owns the address range it used to hand out, so it falls back to a fixed management address of its own. On Virgin Media hubs, for example, the documented behaviour is that the page you used at 192.168.0.1 moves to 192.168.100.1, and that is where you go to turn modem mode back off.
This is worth knowing before you switch, because the obvious conclusion when the old address stops responding is that you have broken something.
When it is worth doing
- You want a router with capabilities the supplied hub does not have — proper VLANs, site-to-site VPN, or granular firewall control.
- You are running two layers of routing and want to remove the double translation that causes.
- Your coverage problem needs a mesh system or access points the hub cannot drive.
When it is not
It does not make your line faster. The speed you get is the speed your provider sells you, and no equipment change alters that. If speed is the actual problem, Test your broadband speed first so you know what you are dealing with.
In modem mode the hub provides no firewall at all. Everything protecting your network becomes your router's job, so it needs to be a device you keep patched.
