第一章 网络互联 Internetworking

摘要

CCNA考点

• Describe how a network works>
• Describe the purpose and functions of various network devices
• Select the components required to meet a network specification
• Use the OSI and TCP/IP models and their associated protocols to explain how data flows in a network
• Describe common networked applications including web applications
• Describe the purpose and basic operation of the protocols in the OSI and TCP models
• Describe the impact of applications (Voice over IP and Video over IP) on a network
• Interpret network diagrams
• Describe the components required for network and Internet communications
• Identify and correct common network problems at layers 1, 2, 3, and 7 using a layered model approach
• Differentiate between LAN/WAN operation and features
• Configure, verify, and troubleshoot a switch with VLANs and interswitch communications
• Explain network segmentation and basic traffic management concepts
• Implement an IP addressing scheme and IP Services to meet network requirements in a medium-size Enterprise branch office network
• Explain the operation and benefits of using DHCP and DNS
• Configure, verify, and troubleshoot basic router operation and routing on Cisco devices

章节顺序

1. Internetworking basics
2. Network segmentation
3. How bridges, switches, and routers are used to physically and logically segment a network
4. How routers are employed to create an internetwork

1.1 网络互联基础 Internetworking Basics

1. 模拟一个交流场景 Bob -=- HUB -=- Sally
   1. This network is actually one collision domain and one broadcast domain
   2. they’re both on the same LAN connected with a multiport repeater (a hub).
   3. Bob is actually going to use Sally’s MAC address to get ahold of her.
   4. How to get MAC?
      （更多…）

4.1　TCP 连接

4.1.1　TCP的可靠数据管道

1. HTTP实际上就是TCP连接及其使用规则
2. TCP 为 HTTP 提供了一条可靠的比特传输管道

4.1.2　TCP流是分段的、由IP分组传送

1. TCP 的数据是通过名为 IP 分组（或 IP 数据报）的小数据块来发送的。
2. HTTP 要传送一条报文时，会以流的形式将报文数据的内容通过一条打开的 TCP 连接按序传输。TCP 收到数据流之后，会将数据流砍成被称作段的小数据块，并将段封装在 IP 分组中，通过因特网进行传输
3. 每个 TCP 段都是由 IP 分组承载，从一个 IP 地址发送到另一个 IP 地址的。每个 IP 分组中都包括：一个 IP 分组首部（通常为 20 字节）；一个 TCP 段首部（通常为 20 字节）；一个 TCP 数据块（0 个或多个字节）。
4. IP 首部包含了源和目的 IP 地址、长度和其他一些标记。TCP 段的首部包含了 TCP 端口号、TCP 控制标记，以及用于数据排序和完整性检查的一些数字值。

4.1.3　保持TCP连接的持续不间断地运行

1. TCP 是通过端口号来保持所有这些连接的正确运行的。

2. TCP 连接是通过 4 个值来识别的：<源IP 地址、源端口号、目的IP 地址、目的端口号>