> Some NAT devices support various methods of intentionally opening ports from the inside. The most common of these is called Universal Plug-and-Play (UPnP).
UPnP should be avoided whenever possible. It's a hideous protocol. NAT-PMP (originally from Apple, now RFC6886) is dramatically simpler and ideal for small networks. Its successor NAT-PCP (RFC6887) is only slightly more complicated in order to better deal with large enterprise networks.
UPnP should be avoided whenever possible. It's a hideous protocol. NAT-PMP (originally from Apple, now RFC6886) is dramatically simpler and ideal for small networks. Its successor NAT-PCP (RFC6887) is only slightly more complicated in order to better deal with large enterprise networks.