How does NAT actually work step by step?
ben31833 · posted · 94 views
I understand the concept of NAT (private IPs to public) but the details confuse me. What are inside local, inside global, outside local, outside global? And how does PAT track which internal device made which request? A step by step walkthrough would really help.
- The inside/outside local/global naming is the hardest part. Just remember: "inside local" is the real private IP on your LAN (like 192.168.1.10). "Inside global" is what the internet sees it as (your public IP). The "outside" versions are usually the same — the real IP of the remote server. — itayitayy,
- PAT is the one everyone actually uses in the real world. Your home router does PAT right now — one public IP, and it uses port numbers to track which internal device made which request. PC1 gets port 40001, PC2 gets port 40002. When a reply comes back to port 40002, the router knows it goes to PC2. — 22maya2n2,
- Build a NAT lab here with 2 PCs behind a router. Configure ip nat inside source list 1 interface gi0/1 overload and watch the translation table with show ip nat translations. You'll see the port mappings appear in real time. It makes the whole concept concrete. — NivSa,
- Inside local = real private IP, inside global = public face. That two-word summary is going straight into my notes. The four terms always felt like they were designed to confuse people but this framing actually sticks. — ben31833,
- Just built the lab you described. The show ip nat translations output is so satisfying — you can literally watch the mappings appear as each PC pings out. Seeing the port numbers change per session makes PAT click instantly. — ben31833,
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