I know Unity supports it, they also support a punch through host where, in the event
that NAT Punch Through isn't valid, they use a type of networking pattern to allow hosts to connect through some Master Server which basically just forwards network requests.
We don't have the infrastructure to do a relay server. Basically for our users it's port forward, and with some luck UPnP will make that unnecessary else, or you're screwed.
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If this can reduce our port forwarding support topics by 50% I'd be thrilled.Â