Hi,
the simplest way would be using the LAN Mode by connecting a Laptop with Network Cable to your Router or using Wifi connection to be in the same network.
Back in 2010 it was also possible just knowing your host IPv4 Adress that you message the friend you gonna play with.
So they can basicly use "Directconnect via IP".
Problem with that is, that IPv4 adresse ran out and Providers are using Techniques to share them between multiple users. The sad fact is, you can´t enter or join a IPv6 adress because the game won´t allow it.
Therefore the netcode of the game need to be changed to allow ipv6 Adresses and utilisisation.
Seems to be quite work intense because there was no mod i have seen, which had this function.
So for the moment you could use Hamachi, Gameranger (still bugged at least for armada2) or a virtuall Private Network
tool from any provider even from the router.