set up the firewall
By default, Construct 2 previews on ports 50000-50100. This can be changed in the Preferences dialog as well, but for now let's assume it's port 50000. If you change it remember to change it in the following steps listed here as well.
Most computers have firewalls, which is security software that blocks unknown connections from other computers. The firewall will probably block inbound connections on port 50000, which will prevent other devices on the network seeing the preview. To fix this, you must set up a rule that allows inbound connections on ports 50000-50100 on the computer running the preview.
The following steps apply to Windows Firewall, which comes with Windows Vista and newer and is one of the most commonly installed firewalls. If you use different firewall software hopefully the steps are not too different and you can still follow along.
First, open Windows Firewall settings. It's in Control Panel's System and Security section. Click Advanced settings on the left. (You must have administrator permissions to do this.)
Click Inbound Rules on the left, then New Rule... on the right.
For What type of rule would you like to create?, select Port and click Next.
Leave TCP selected, and for Specific local ports enter 50000-50100. (You'll need to enter something different if you changed the Port setting in Construct 2's preferences.) Note a range is used because Construct 2 can use higher ports if the given one is use. Click Next when you're done.
The next page doesn't need changing - leave it on Allow the connection. Click Next.
For When does this rule apply? you should untick 'Public' unless you want to share previews over public networks like public Wifi hotspots. Click Next.
You can enter a name and description for this rule. The name Construct 2 Preview on LAN would be appropriate.
Click Finish. You're all done! You can close the firewall windows now.
The next section will show you how to preview on a LAN now that it's set up.