Network Basics

What this chapter covers

Network Basics is 10% of the Huawei HCIA-Security H12-711 exam. It covers the OSI and TCP/IP reference models, how data is encapsulated and decapsulated, the common protocols and port numbers at each layer, and the devices that build a network: switches, routers, firewalls and other security devices.

Questions are single-answer, multiple-answer without a stated count, true/false, drag and drop and typed fill-in-the-blank, often "Which of the following statements is true?". Some show a firewall topology figure or display output and ask which layer a field belongs to or how a device handles a frame or packet.

It has 2 outline topics, and two pages cover them.

How the topics fit together

The reference model gives every protocol and every device a layer. Once you know the layers, you know what each device looks at: a switch reads MAC addresses, a router reads IP addresses, and a firewall reads addresses, ports, sessions and even applications.

Learn the layers and their protocols first, then map each device onto them. Most security features later in the course depend on this mapping.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with tables and examples.
• What to remember for the exam: the facts to memorize.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

For each protocol or field you meet, say its layer before reading on. The exam often asks which layer a protocol works at, or which device can act on a given header.