JSI Tip 9812. What are the DirectX ports required to play on a network?

Microsoft Knowledge Base Article 240429 contains the following summary:

This article describes the default ports that are required to play Microsoft Windows DirectX multiplayer games through a firewall, a proxy server, a router, Network Address Translation (NAT), or Internet Connection Sharing. For the specific ports that are required by your game, see the game product documentation. For the ports that are required by games that are published by Microsoft, visit the following Microsoft Web site:

http://support.microsoft.com/games