Game not working on LAN

Hey

I tried to play with a friend at home but it will not work. We are on the same network with the same subnet and I added firewall rules for the ports 1000-1005 manually to the windows firewall but without any success.

I am able to play with my friends over WAN but on LAN nothing seems to work.

It seems like the client is trying to connect to the other computer using the public IP-Address and not the local address... at least this is how it looks on my Sophos UTM:
11:41:14 Default-DROP UDP
[PUBLIC]: 61380
→
[PrivateGW] : 1000

len=68 ttl=127 tos=0x00 srcmac=e0:2****:05:82 dstmac=00:15****55:1a

 

OK I guess I found out which setting to change but I can not change the ports. The textfield seems to be disabled and no setting enables it. Can I change this directly in the xml and if so what is the schema?