I'm only using Windows Firewall, which allows DEFCON as an exception, turning the firewall off did nothing. I've tried port-forwarding alongside having the option for PF enabled in the game options, no luck. Here's my debug.txt:
Defcon 1.61 STEAM built Dec 1 2011
Parsing archive main.dat...DONE
Found language 'english' with caption 'English' in 'data/language/english.txt'
Found language 'french' with caption 'Français' in 'data/language/french.txt'
Found language 'german' with caption 'Deutsch' in 'data/language/german.txt'
Found language 'italian' with caption 'Italiano' in 'data/language/italian.txt'
Found language 'spanish' with caption 'Español' in 'data/language/spanish.txt'
WinSock started
Client listening on port 5011
Parsing Coastline data (1864 islands) : 0ms
Parsing International data (2753 islands) : 0ms
Parsing City data (2745 cities) : 0ms
Parsing archive sounds.dat...DONE
Authentication key set : 'STEAMT-WEGARP-BOZIBR-JZCKBS-RCY'
WinSock started
Connection established to MetaServer on port 5008. Listening on Port 5008
SteamAPI_Init SUCESS
Steam Authentication Initiated
Steam Authentication : Logging On To Steam
Steam Authentication : Getting Steam Id
Steam Authentication : SteamID = 76561198021743220
Steam Authentication : Getting Steam3 Auth
Requesting authentication of key STEAMT-WEGARP-BOZIBR-JZCKBS-RCY
Steam Authentication : Requesting Authentication
Received Authentication : STEAMT-WEGARP-BOZIBR-JZCKBS-RCY : (keyID 7413437) : Accepted
Authentication HashToken set to -1931927951
CLIENT : Disconnected
EclRemoveWindow failed on window LOBBY
Local IP address is: 192.168.0.13
WinSock started
Server started on port 5010
CLIENT : Attempting connection to Server at 192.168.0.13:5010...
CLIENT : Disconnected
SERVER : Shutting down...
SERVER : Shut down complete
Disconnected from MetaServer