Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network engineer is configuring a new Cisco router to provide Internet access for a small office. The office uses private IPv4 addresses (10.0.0.0/8) internally, and the router has a single public IPv4 address assigned to its WAN interface. The engineer needs to configure a mechanism that allows multiple internal devices to share this single public IP address when accessing the Internet. Which IP service should be configured?
- AIPv6 Transition Mechanisms
- BDynamic NAT
- CPAT (Port Address Translation)
- DStatic NAT
Show answer & explanationAnswer & explanation
Correct answer: C. PAT (Port Address Translation)
PAT (Port Address Translation), also known as NAT Overload, allows multiple internal private IP addresses to share a single public IP address by translating both the IP address and the port number. This is the most common method for small offices to access the Internet with a single public IP.
Why the other options are wrong
- A. IPv6 Transition Mechanisms are for migrating from IPv4 to IPv6, not for sharing a single public IPv4 address.
- B. Dynamic NAT maps a pool of private IPs to a pool of public IPs, but still requires multiple public IPs for simultaneous connections.
- D. Static NAT maps one private IP to one public IP, not suitable for multiple internal devices sharing one public IP.
PAT (Port Address Translation)
A form of network address translation where multiple private IP addresses are mapped to a single public IP address using different port numbers.
- Also known as NAT Overload.
- Allows many-to-one IP address translation.
- Conserves public IPv4 addresses.
Memory trick: PAT lets many private homes share one public post office.