About this interactive
Source and destination swap between a request and its reply, so Cisco names NAT addresses by two things that do not change:
- **Inside or outside**: which host. Inside is the device on your network (the laptop, your web server); outside is the device beyond it (the internet server).
- **Local or global**: where the packet is. Local is the address in the header on the inside network; global is the address in the header out on the internet.
So the laptop's 10.1.10.34 is **inside local**, the public address it is translated to is **inside global**, and the web server is **outside global** on the internet and **outside local** as the inside sees it. Without outside translation, the two outside addresses are the same number. The router keeps each translation in its NAT table so replies find their way back.
What you'll learn
- Name each address in a NAT translation as inside local, inside global, outside local or outside global, whichever way the packet is going
- Explain why Cisco uses inside and outside (which host) and local and global (which side of the router) instead of source and destination
Aligned to
Cisco CCNA
4.1
Configure and verify inside source NAT using static and pools
Key terms
- Inside Local Address
- The private IP address assigned to a device on the internal network before NAT translation occurs.
- Inside Global Address
- The public or routable IP address that represents an inside device after NAT translation to the outside network.
- Outside Local
- The IP address of an outside destination host as seen from within the local network, found in the IP header before translation.
- Outside Global
- The IP address of an outside destination host as seen from the public network, found in the IP header after translation.
- NAT Table
- A translation table maintained by a NAT-enabled router that records mappings between inside local and inside global addresses to ensure return traffic is correctly forwarded.
Topics
Nat
Nat Terminology
Inside Local
Inside Global
Outside Global
Interactive
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