Overview: Address translation and port mapping
Address translation and port mapping relate internal endpoints to the addresses and routes visible elsewhere.
One home router, two translation layers and a carrier-managed translation boundary create different reachability conditions. Loopback and UPnP mappings address further cases within that arrangement. These topics explain which endpoint is exposed and which device controls the relevant mapping.
Network address translation (NAT)
NAT rewrites endpoint addressing across network realms, with address/port translation retaining state that associates outside traffic with the intended inside flow.Port forwarding
Port forwarding maps a selected inbound endpoint to an internal service, with address stability, firewall policy and service readiness determining whether the complete request can succeed.Double NAT
Double NAT places two translation boundaries in a connection path, requiring their endpoint mappings and state to compose before outside traffic can reach an internal server.Carrier-grade NAT (CGNAT)
Carrier-grade NAT places subscriber traffic behind an operator-controlled translation layer, so household gateway settings do not necessarily provide an outside inbound service mapping.NAT loopback
NAT loopback lets an inside client use an outside mapped endpoint for an inside service, with compatible translation and return routing keeping the client’s expected peer consistent.UPnP port mapping
UPnP gateway port mapping asks a compatible gateway to maintain an inbound endpoint association, with granted mapping details and lifetime distinct from complete server reachability.