1.Go to the Control Panel and launch Windows Firewall.
2.Go to Advanced Settings
3.Select Inbound Rules in the left pane
4.Select New Rule in the right pane
5.In the New Inbound Rule Wizard, select Port as Rule Type, then click on Next
6.Select TCP and put 900 (and any other ports you want to open) in Specific local ports, then click on Next
7.Select Allow the connection, then click on Next
8.Select the network location where the rule should apply (select them all if you're not sure), then click on Next
9.Give a name and an optional description