DoD (TCP/IP) Stack — OSI Network Layer Equivalent In the four-layer DoD model (Application, Host-to-Host, Internet, Network Access), which layer corresponds functionally to the OSI Network layer (Layer 3)?

Introduction / Context:
Cross-mapping OSI and TCP/IP models is a frequent exam topic and helps engineers translate conceptual discussions across documents and vendors. The OSI Network layer is responsible for logical addressing and routing across internetworks.

Given Data / Assumptions:

• We use the DoD 4-layer view: Application, Host-to-Host, Internet, Network Access.
• OSI Network layer (Layer 3) handles IP addressing, routing, and path selection.
• We must map functions, not names.

Concept / Approach:
The DoD Internet layer provides routing and logical addressing (for example, IP, ICMP, routing protocols), matching OSI Layer 3 responsibilities. The Host-to-Host layer aligns with OSI Transport (TCP/UDP), and Network Access aligns with OSI Data Link and Physical. Therefore, the functional equivalent of the OSI Network layer is the Internet layer in the DoD model.

Step-by-Step Solution:
Identify OSI L3 functions: addressing and routing.Locate those functions in DoD: Internet layer.Exclude Host-to-Host (transport) and Network Access (link/physical).Select Internet.

Verification / Alternative check:
Protocol placement: IP and ICMP reside in the Internet layer, just as OSI Layer 3 would house network protocols.

Why Other Options Are Wrong:

• Application: Upper-layer protocols and services, not routing.
• Host-to-Host: End-to-end transport, not network-wide routing.
• Network Access: Framing and media access, not logical addressing.

Common Pitfalls:
Confusing the term "Internet" (the global network) with the Internet layer name; here it refers to the TCP/IP layer where IP operates.

Final Answer:
Internet