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Question

Difficulty: EasyNAT and PAT Implementation

A network administrator is evaluating Network Address Translation options for a small remote office where 50 internal devices with private IPv4 addresses need simultaneous internet access using only one assigned public IPv4 address. Which of the following statements accurately describe how Port Address Translation (PAT) fulfills this requirement? (Select TWO.)

  1. PAT tracks individual outbound client connections by appending unique Layer 4 source port numbers to the shared public IP address.Answer
  2. PAT modifies both the source IP address and the source port number in outbound IPv4 packet headers.Answer
  3. C
    PAT requires a dedicated, static one-to-one mapping between each internal private IP address and a unique public IP address.
  4. D
    PAT operates exclusively at Layer 2 of the OSI model by rewriting Ethernet frame MAC addresses.

Answer

Port Address Translation (PAT) tracks outbound sessions by appending unique Layer 4 source port numbers to the single public IP address, modifying both the source IP address and source port number in outbound packet headers.
Port Address Translation (PAT) allows multiple private IPv4 hosts to share a single public IPv4 address simultaneously by translating both the source IP address (Layer 3) and source port number (Layer 4) for outbound packets, using distinct port numbers to track return traffic for each host.

Step-by-Step Solution

1
Identify the scenario requirement
50 internal hosts with private addresses must share a single public IP address simultaneously.
Because only one public IP address is available, traditional one-to-one Static NAT or Dynamic NAT without port translation cannot support all hosts concurrently.
2
Analyze how PAT operates at Layer 3 and Layer 4
PAT assigns a unique source port number to each session originating from an internal host.
By distinguishing traffic flows using Layer 4 TCP/UDP port numbers alongside the single public Layer 3 IP address, thousands of concurrent sessions can share one IP address.
3
Evaluate packet translation behavior
Outbound packets undergo translation of both their internal source IP address and internal source port number.
The router/firewall updates the header fields so return traffic from the internet is directed back to the public IP and translated port.

Key Concept

Port Address Translation (PAT / NAT Overload)
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Topics

NAT and PAT Implementation

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