Probably you already read that Message and landed here because of this:
This lobby is not joinable. Players in the lobby may have different NAT types than yours, which can limit network features.
COD BLACKOUT is another Call of Duty with a "interesting" Network Code. Different than BF the COD Series relies on P2P Matchmaking instead of Dedicated Servers. So because now Everybody is "a Server" this can cause some Trouble if you are behind a more or less restricted Internet Connection. Specially Campus or Company connects share one broadband Line to many users. Unlike normal home users, you have to be more economic with port ranges here. But also some Home Routers use more restrictive types of NAT (Network Adresse Translation).
Imagine your Internet Connection like a big flat with Hundert of apartments in. To get a package delivered you need to be specific with the Road + Nr + Apartment Nr. Those Partment Numbers are our Ports; Blackout, in this case, need to receive incoming packages on that number. Normally you have a Protocol to handle those Dynamically, UPnP but blackout unfortunately demands only one Port - 3074. If that is not available it most time just give you an Error Message.
So to avoid Conflicts 1st be sure UPnP is enabled on your Router, or alternatively set up a static forwarding of UDP Port 3074 to your Gaming PC.
Solution example with pfSense
I use a pfSense Router at home, at work and on Events - because pfSense is simply a great piece of Software :) In this Example, I show you the configuration you need to configure your pfSense based router to correctly NAT blackout.First, we're going the UPnP way - because we can restrict it per IP that's totally fine for home Networks.
1) Your Interface connected to Internet, normally WAN
2) The Interface where your Gaming PC is connected, normally LAN
3) We deny the use of UPnP per default, so only later allowed Rules are applied and allowed
4) We do allow our Gaming PC (IP: 172.16.50.10) to crerate UPnP requests from 53-65535
The Range we choose at 4 is actually much more then we would need for COD Blackout. But some games, especially XBOX ports to PC often require a wide array of ports.
To make it fully working we also need to fix the ports in our NAT Rule, to achieve that open Firewall > NAT > Outbound.
First set the Rule Generation here to Hybrid, add a new rule as follows:
1) Your Internet (WAN)
2) You want to stay with TCP/UDP
3) All traffic from your Gaming Machine - so give the PCs IP here
4) choose interface Address
5) Important, tick - Static Port; That's all we doing it for
After all those Settings apllied to the firewall be sure to restart the PC to reset all it's UPnP tries from before. Now you should be able to connect to the blackout lobby withotu the different NAT Error. After starting blackout the pfSense Status for UPnP should show you a UPnP Mapping of Port 3074/udp coming from DemonwarePortMapping.
Simple or other routers
Instead of going all this UPnP hulabalou you can try to make a portforward in your router to your local Gaming PC. Be sure to forward incoming Traffic of following Ports to your Gaming PC:TCP: 3074, 27014-27050
UDP: 3478, 4379-4380, 27000-27031, 27036
UDP: 3478, 4379-4380, 27000-27031, 27036
More elegant is the UPnP method described above.
gl hf
