Add prerequisites for hosting

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 ## Hosting a server with Northstar
 
+* [Prerequisites](hosting-a-server-with-northstar/prerequisites.md)
 * [Hosting a Basic Listen Server](hosting-a-server-with-northstar/basic-listen-server.md)
 * [Hosting a Dedicated Server](hosting-a-server-with-northstar/dedicated-server.md)
 
diff --git a/hosting-a-server-with-northstar/prerequisites.md b/hosting-a-server-with-northstar/prerequisites.md
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+**TL;DR:** Port forward `37015` (UDP) and `8081` (TCP)
+
+# Prerequisites:
+
+Make sure you already installed Northstar [as described here](Installing-Northstar).
+
+## Check whether you can port forward:
+
+In order for others to join your game they need to be able to reach you. Most likely your router acts as a NAT so you need to port forward two ports to your PC for [NAT traversal](https://en.wikipedia.org/wiki/NAT_traversal).
+
+## CGNAT
+
+First we want to make sure you're not behind a [CGNAT](https://en.wikipedia.org/wiki/Carrier-grade_NAT) as this basically means you won't be able to host at all.
+
+For this find out your external IP address [by visiting this site](https://www.whatsmyip.org/).
+
+Then [open CMD](https://www.lifewire.com/how-to-open-command-prompt-2618089#toc-open-command-prompt-in-windows-10) and type in:
+
+```
+tracert <your external IP address here>
+```
+
+if only your external IP address shows up when the commands exits you're good.
+
+
+If you get 2 entries or more you're likely behind a [CGNAT](https://en.wikipedia.org/wiki/Carrier-grade_NAT). Your only options in this case are either to ask your ISP to give you a public IP address or check whether at least your IPv6 address is public.
+
+## Port forwarding
+
+Access your router via it's web interface and port forward
+
+- `37015` (UDP) for game logic
+- `8081` (TCP) for Northstar auth so your server shows up in server browser
+
+to your PC that you're running Northstar on.
+
+## Final checks
+
+To check whether you set everything up correctly, start the game via Northstar and go into a private match. Another Northstar user should now be able to see your server on the server browser.  
+Note that by default your server is called `Unnamed Northstar Server`. You can change this as described below.
+
+## Extras:
+
+Northstar uses a config file to set various settings for your custom server. The file is located at `Titanfall2\R2Northstar\mods\Northstar.CustomServers\mod\cfg\autoexec_ns_server.cfg`
+
+In particular:
+- `ns_server_name` sets the name of your server on the server browser. You probably want to change this to something the people you play with recognise.
+- `ns_auth_allow_insecure` decides whether to allow players not authenticated with Northstar master server. Change the value from `0` to `1` if you want to play with vanilla clients. To find out what else you need to do for vanilla clients to join, read [the instruction for setting up Northstar for PUGs](Northstar-PUGs-Setup).
+