SSCP Question #846: Real Exam Question with Answer & Explanation

The correct answer is D: Network layer. NAT (Network Address Translation) operates at Layer 3 - the Network layer - of the OSI model because it modifies IP address information in the headers of IP packets as they transit a router or firewall. Specifically, NAT rewrites the source or destination IP address (and sometime

Submitted by jordan8· Apr 18, 2026Network and Communications Security

Question

Upon which of the following ISO/OSI layers does network address translation operate?

Options

ATransport layer
BSession layer
CData link layer
DNetwork layer

Explanation

NAT (Network Address Translation) operates at Layer 3 - the Network layer - of the OSI model because it modifies IP address information in the headers of IP packets as they transit a router or firewall. Specifically, NAT rewrites the source or destination IP address (and sometimes port numbers, in the case of PAT/NAPT) to translate between private internal addresses and public routable addresses. Since IP addresses are a Layer 3 construct, NAT is inherently a Network layer function. Some advanced NAT implementations also inspect transport-layer port numbers, but the core address translation is firmly at Layer 3.

Topics

#Network Address Translation (NAT)#OSI Model#Network Layer#IP Addressing

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