NAT overload - usually called PAT (Port Address Translation) - shares a SINGLE outside IP across many inside hosts by tracking the source port. Each internal connection gets a unique source port from the perspective of the outside; the router maintains the port-to-host mapping in its translation table. The vast majority of "NAT" in production is actually PAT. This lab configures PAT on R2 sharing Et0/1's IP across all inside hosts.
What you will learn
- PAT configuration with the
overloadkeyword - How PAT maps multiple inside hosts to one outside IP using source ports
- The translation table format with port columns
- Why PAT is the dominant NAT pattern in 2026
What this lab does NOT cover
- PAT with a pool (overload + pool combined)
- Inside source vs outside source PAT (rare)
Topology
Download the CCNA Base Topology .yaml
3 iol-xe routers + 1 alpine + 1 ioll2-xe managed switch + 1 unmanaged switch. The reusable foundation for the PingLabz CCNA Labs library.
