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Difficulty: HardNAT and PAT Implementation

A network engineer is reviewing an active translation table on a corporate edge gateway to verify Port Address Translation (PAT) functionality. An internal client workstation with the private IP address 172.16.10.50172.16.10.50 initiates an HTTPS session to an external web server at 198.51.100.25:443198.51.100.25:443. The gateway translates all outbound traffic using its single public interface IP address of 203.0.113.1203.0.113.1. As the outgoing IP packet leaves the firewall's public interface toward the destination server, which address and port combination accurately represents the Inside Global identifier for this session?

  1. 203.0.113.1203.0.113.1 paired with a dynamically assigned high-numbered source port (such as 5214452144)Answer
  2. B
    172.16.10.50172.16.10.50 paired with a dynamically assigned high-numbered source port (such as 5214452144)
  3. C
    203.0.113.1203.0.113.1 paired with destination TCP port 443443
  4. D
    198.51.100.25198.51.100.25 paired with destination TCP port 443443

Answer

The Inside Global address and port combination is the firewall's public IP address (203.0.113.1203.0.113.1) combined with a dynamic high-numbered source port (such as 5214452144).
The correct answer identifies that in NAT/PAT terminology, the Inside Global address represents the internal host as it appears to the outside network. Under Port Address Translation (PAT), the firewall replaces the private source IP with its own public WAN interface IP (203.0.113.1203.0.113.1) and substitutes the original source port with a uniquely allocated high-numbered ephemeral port (such as 5214452144) to maintain connection state mapping.

Step-by-Step Solution

1
Identify the standard CompTIA NAT terminology definitions.
Inside Local is the private client IP/port (172.16.10.50:ephemeral172.16.10.50:ephemeral). Inside Global is the public translated IP/port representing the client to the internet (203.0.113.1:translated_port203.0.113.1:translated\_port). Outside Global is the target public IP/port (198.51.100.25:443198.51.100.25:443).
CompTIA Network+ standard definitions differentiate internal local private addresses from internal global public translated addresses.
2
Analyze the impact of Port Address Translation (PAT / NAT Overload).
PAT tracks individual outbound client connections by swapping the original private source IP and source port with the public gateway IP and a newly assigned high-numbered ephemeral port.
Multiple internal hosts share a single public IP address by keeping sessions distinct at Layer 4 using unique source port numbers.
3
Determine the specific Inside Global entry for the packet exiting the WAN interface.
The packet on the public network displays the source IP 203.0.113.1203.0.113.1 and a dynamically generated source port (e.g., 5214452144).
This unique combination allows the gateway to map return traffic back to the originating client (172.16.10.50172.16.10.50).

Key Concept

NAT Terminology and PAT Port Assignment Mechanics
Estimated Time:2m 0s
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Topics

NAT and PAT Implementation

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