NAT Interactive Classroom Trainer & Knowledge Quiz

Why Does NAT Exist?

The IPv4 address space only has about 4.3 billion addresses, which quickly ran out as the internet grew. To solve this, networks use Private IPv4 Addresses (RFC 1918) internally (such as 192.168.x.x, 10.x.x.x, and 172.16.x.x–172.31.x.x).

However, private IP addresses cannot be routed on the public internet. Internet routers immediately drop packets with private source or destination IPs. Network Address Translation (NAT) runs on your border router or firewall to rewrite private IP addresses into routable public IP addresses as packets leave your network—and translates replies back to the right internal device when they return.

Interactive NAT Address Terminology

Click each term below to see how a NAT router classifies addresses during a connection from an office PC to a public web server:

Inside Local Address (192.168.1.10)

The private IPv4 address assigned to a host on the inside (private) network before NAT translation occurs. Only devices inside your local LAN see this address.

1-to-1 Permanent Static NAT

Static NAT

Manually maps one specific private IP to one dedicated public IP permanently.

Direction: Allows inbound & outbound initiation
Best for: Internal web, mail, or VPN servers that outside users must reach
Drawback: Consumes 1 public IP per server even when idle

1-to-1 Pool Lease Dynamic NAT

Dynamic NAT

Dynamically assigns an available public IP from a pre-configured pool on a first-come, first-served basis.

Direction: Outbound-initiated sessions
Best for: Organizations needing temporary dedicated 1:1 public IPs per active host
Drawback: If all pool IPs are in use, additional hosts are blocked (pool exhaustion)

Many-to-1 + Ports Port NAT / PAT

Port NAT (PAT / Overload)

Maps hundreds or thousands of private IPs to a single public IP by tracking unique TCP/UDP source port numbers.

Direction: Outbound-initiated (unless port-forwarded)
Best for: Homes, schools, and enterprises conserving public IPv4 space
Key feature: Rewrites source port on collision so every session is unique

Interactive NAT Router & Packet Simulator

Select a NAT flavor below, then trigger packets to watch how the router rewrites headers and updates its translation table.

Inside Network (Private LAN) 192.168.1.0/24

NAT Border Router

Last Packet Inspection Ready

Click any host action button to send a packet through the NAT router.

Outside Network (Internet) Public IPv4

Public Cloud Server

198.51.100.80 : 443 (HTTPS)

Only knows how to route back to public Inside Global addresses—never private 192.168.1.x IPs.

Router# show ip nat translations

0 active entries

Protocol	Inside Local (Private)	Inside Global (Public)	Outside Global (Remote)	Type / Status

Why Choose One Flavor of NAT Over Another?

Each NAT flavor solves a different architectural requirement. Compare their trade-offs below and test yourself with real-world network design scenarios.

Feature / Criteria	Static NAT	Dynamic NAT	Port NAT (PAT / Overload)
Mapping Ratio	Fixed 1-to-1 (Permanent)	Temporary 1-to-1 (From Pool)	Many-to-1 (Uses TCP/UDP Ports)
Public IP Efficiency	Low (1 Public IP per host)	Medium (Requires a pool of Public IPs)	High (1 Public IP supports ~65,000 sessions)
Inbound Connections from Internet?	Yes — Predictable, permanent public IP	No — Mapping only exists after outbound traffic & IP changes	No by default (unless explicit Port Forwarding is configured)
What Happens Under Heavy Load?	Always available for the single mapped server	Pool Exhaustion: Once all pool IPs are leased, new hosts are dropped	Scales seamlessly by assigning new source port numbers
Primary Real-World Use Case	Hosting public-facing servers (Web, Mail, DNS, VPN gateway) inside a private DMZ	Legacy protocols that forbid port changes, or strict external IP logging per active user	Home networks, schools, and enterprise employee internet access

Interactive Architecture Advisor: Click a Scenario

Recommended: Port NAT (PAT / NAT Overload)

With 400 student laptops browsing the web simultaneously and only 1 or 2 public IPv4 addresses provided by the ISP, Port NAT (PAT) is essential. It multiplexes all 400 internal private IPs onto a single public IP by tracking each connection's unique TCP/UDP source port number.

NAT Knowledge Check (5 Questions for Classroom Credit)

Enter your student information below, answer all 5 questions, and click Submit Quiz & Generate Credit Receipt to turn in your work.

Student Full Name *

Student ID / Class Period *

Date

Network Address Translation (NAT) Explorer