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ISC2-CC - Network Security - Section 4.1

Understand computer networking fundamentals, including the OSI and TCP/IP models, IP addressing, and common ports and protocols.

Identify the layers of the OSI and TCP/IP models and the function each performs, and recognise common protocols and their well-known ports - HTTP (80), HTTPS (443), SSH (22), DNS (53), and RDP (3389). Distinguish IPv4 from IPv6 addressing and the role of public versus private address ranges.

OSI modelTCP/IP modelCommon portsIP addressingProtocols

Practice question for this objective

Free sampleNetwork Securitymedium

A support engineer is mapping where the HTTP, DNS and SMTP protocols sit within the four-layer TCP/IP model so she can explain the stack to a new hire. Into which TCP/IP layer do these three protocols fall?

  • ATransport layer
  • BApplication layer Correct
  • CInternet layer
  • DNetwork access layer
In the TCP/IP model, HTTP, DNS and SMTP are Application-layer protocols that sit above transport and routing. The four-layer TCP/IP model collapses the top OSI layers into a single Application layer, where protocols such as HTTP, DNS and SMTP operate, while transport services and IP routing are provided by the lower Transport and Internet layers.

Why A is wrong: These protocols do rely on TCP or UDP, which makes this tempting, but that reliance is on the Transport layer's services rather than the layer where the protocols themselves live.

Why B is correct: HTTP, DNS and SMTP are all application protocols that generate and interpret user-facing data, so in the TCP/IP model they sit at the Application layer.

Why C is wrong: Traffic is routed at the Internet layer, so it seems plausible, but this layer handles IP addressing and routing, not application protocols.

Why D is wrong: This layer is the foundation of the stack, which can distract, but it deals with physical transmission and framing, not with HTTP, DNS or SMTP.

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