Slitherine

If you use a connection with router (example Adsl router , LAN ,ecc) for internet connection ,isn't possible to host games , only join other matchs of others players.

This is normal for NAT connections.

Arena actually supports NAT negotiation (for example, all the development team are behind NAT firewalls). However, there are many firewall configs that will never allow the user to host. But as you say, you should be able to join a game if that is the case.

But in general, if you are behind a home-type hardware NAT you should have no problems playing online.

Cheers

Pip