Router Blah

In reading a BitTorrent FAQ to find out more about the protocol (specifically trackers) work, I needed clarification on how "modern" NAT routers do their thing. I referred to a couple online docs that were pretty helpful. The How Stuff Works article is widely quoted.

OpenBSD FAQ on NAT
How Network Address Translation Works

When I reasoned my way through NAT after reading the IP and TCP RFCs (in 1997, before I knew of its existence, which was 1994 according to RFC 1631), it made sense to rip out the original IP address and TCP port address. However, some protocols like FTP include the IP address, making NAT even more invasive and complex. BT's protocol is pretty simple, relatively speaking. The trouble with NAT is the lack of bidirectional protocol capability across multiple machines. Using port forwarding, it's possible to do this on a single designated host.

Now there's "UPnP", but it's unclear at this point if there are any security issues exploitable from the protocol itself. There are several sub-standards (pun?), such as Basic Device, Internet Gateway Device, Wireless LAN Access Point, and even for HVAC (Heating, Ventilation, and Air-Conditioning).