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Difficulty: MediumNAT and PAT Implementation

A network administrator is auditing the stateful address translation table on an edge firewall configured with Port Address Translation (PAT). Which of the following statements correctly describe how PAT processes outbound traffic and manages network connections? (Select TWO)

  1. PAT maps multiple private IPv4 addresses to a single public IP address by dynamically assigning a unique Layer 4 source port number to each outbound session.Answer
  2. If two internal hosts initiate outbound traffic using identical source port numbers, the edge device modifies the outbound source port to maintain entry uniqueness in its translation table.Answer
  3. C
    PAT requires reserving a dedicated public IPv4 address from a configured pool for each active internal host for the entire duration of its network session.
  4. D
    PAT state tracking operates at Layer 2 of the OSI model by binding internal host MAC addresses directly to public IP mappings in the translation cache.

Answer

The correct statements are that PAT maps multiple private IPv4 addresses to a single public IP address using unique Layer 4 source port numbers, and that the NAT device rewrites egress source ports if two internal hosts attempt to use identical source ports.
Port Address Translation (PAT) allows thousands of internal hosts on private IP addresses to share a single public IP address by tracking sessions using unique Layer 4 TCP/UDP port numbers. If two internal hosts select the same initial ephemeral source port, the PAT gateway alters the translated outbound source port to guarantee a unique translation entry.

Step-by-Step Solution

1
Analyze how PAT handles internal-to-external translation.
Recognize that PAT uses Layer 4 source port numbers (TCP/UDP) alongside a single public IP address to differentiate traffic streams originating from multiple internal private host IP addresses.
PAT (also known as NAT Overload) relies on unique transport-layer port numbers to allow multiple private IP addresses to share one public IP address.
2
Evaluate port collision handling in PAT.
Confirm that if two client hosts pick the same source port number, the translating device rewrites the translated source port number on the WAN side to avoid ambiguous translation table entries.
Maintaining unique (Public IP, Public Port) tuples is necessary for returning traffic to be correctly de-multiplexed back to the originating internal (Private IP, Private Port) client.
3
Identify misconfigurations and incorrect operational descriptions in distractors.
Eliminate options that confuse Dynamic NAT pool assignment with PAT overload, or that incorrectly place PAT tracking at Layer 2 instead of Layer 3/4.
Dynamic NAT allocates 1-to-1 public IP mappings, and address/port translation operates at Network (Layer 3) and Transport (Layer 4) layers.

Key Concept

Port Address Translation (PAT / NAT Overload) session tracking and port rewriting mechanisms
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Topics

NAT and PAT Implementation

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