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Week 14: LAN Devices & Final Exam Prep 第 14 周：局域网设备与期末模拟

Core Concepts 核心概念

1. LAN System Devices (9.4)

  • Network Interface Card (NIC): Physical hardware connecting a computer to the transmission medium, containing a unique physical 48-bit MAC address.
  • Hub (Layer 1 - Physical): Replicates incoming signals to all output ports, creating a single shared collision domain. Inefficient.
  • Switch (Layer 2 - Data Link): Learns MAC addresses of connected devices and selectively forwards frames to target ports. Splits collision domains.
  • Router (Layer 3 - Network): Uses logical IP addresses to route packets between different subnets/networks. Splits broadcast domains.

2. WAN and Wireless Networks (Chapter 10 Intro)

Wide Area Networks (WANs) span large geographical distances, connecting distant LANs using telecom provider lines. Wireless Local Area Networks (WLANs) transmit data packets over-the-air using radio waves (IEEE 802.11 Wi-Fi standard) and access points (APs).

1. 局域网系统设备 (9.4)

  • 网卡 (NIC)： 将计算机连接到传输介质的物理硬件，包含唯一的物理 48 位 MAC 地址。
  • 集线器 (Hub)（第一层 - 物理层）： 将输入信号复制转发到所有输出端口，形成单个共享冲突域。效率极低。
  • 交换机 (Switch)（第二层 - 数据链路层）： 学习连接设备的 MAC 地址，并将数据帧选择性地转发到目标端口。划分冲突域。
  • 路由器 (Router)（第三层 - 网络层）： 使用逻辑 IP 地址在不同子网/网络之间路由数据包。划分广播域。

2. 广域网与无线网络 (第 10 章导论)

广域网 (WAN) 跨越较大的地理距离，使用电信提供商的线路连接遥远的局域网。无线局域网 (WLAN) 使用无线电波（IEEE 802.11 Wi-Fi 标准）和接入点 (AP) 在空中传输数据包。

Concept Visualization: Layer 2 vs. Layer 3 Forwarding 概念可视化：第二层与第三层转发

Host A 192.168.1.10 Switch 1 (L2) Router (L3) Switch 2 (L2) Host B 192.168.2.20 Dest IP: 192.168.2.20 (Constant) Dest MAC: Rewritten at each router hop

Tips 提示

  • MAC vs IP roles in forwarding: When a router forwards a packet from one subnet to another, it rewrites the destination MAC address to the next-hop node's MAC address, while keeping the destination IP address completely unchanged.
  • Broadcast vs Collision domains: A Switch splits collision domains (each port is its own domain) but maintains a single broadcast domain. A Router splits broadcast domains (interfaces drop incoming LAN broadcasts).
  • 转发中 MAC 与 IP 的角色变化： 当路由器将数据包从一个子网转发到另一个子网时，它会将目的 MAC 地址重写为下一跳节点的 MAC 地址，但保持目的 IP 地址完全不变。
  • 广播域与冲突域： 交换机划分了冲突域（每个端口都是独立的物理冲突域），但保留了单个广播域。路由器则能够划分广播域（接口默认丢弃入站的局域网广播数据包）。

Practical Exercises & Step-by-Step Guide 实践练习与分步指南

Exercise 1: Inter-Subnet Routing Configuration 练习 1：子网间路由配置

Steps to configure:

  1. In Packet Tracer, place a 2911 Router. Connect GigabitEthernet 0/0 to Switch1 (LAN1: `192.168.1.0/24`) and GigabitEthernet 0/1 to Switch2 (LAN2: `192.168.2.0/24`).
  2. Configure interface IP addresses on the Router: 
    Router# configure terminal
Router(config)# interface gigabitEthernet 0/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown
Router(config-if)# interface gigabitEthernet 0/1
Router(config-if)# ip address 192.168.2.1 255.255.255.0
Router(config-if)# no shutdown
  3. Configure static IPs on PC-A in LAN1 (IP: `192.168.1.10`, gateway `192.168.1.1`) and PC-B in LAN2 (IP: `192.168.2.20`, gateway `192.168.2.1`).
  4. Click PC-A -> Desktop -> Command Prompt. Run a trace route: tracert 192.168.2.20. Verify that the first hop hits the gateway router interface (`192.168.1.1`).

配置步骤：

  1. 在 Packet Tracer 中，放置一个 2911 路由器。将 GigabitEthernet 0/0 连接到 Switch1（局域网1: `192.168.1.0/24`），将 GigabitEthernet 0/1 连接到 Switch2（局域网2: `192.168.2.0/24`）。
  2. 在路由器上配置接口 IP 地址： 
    Router# configure terminal
Router(config)# interface gigabitEthernet 0/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown
Router(config-if)# interface gigabitEthernet 0/1
Router(config-if)# ip address 192.168.2.1 255.255.255.0
Router(config-if)# no shutdown
  3. 为局域网1中的 PC-A 配置 IP `192.168.1.10`，默认网关 `192.168.1.1`；为局域网2中的 PC-B 配置 IP `192.168.2.20`，默认网关 `192.168.2.1`。
  4. 在 PC-A 的命令行中执行路由跟踪： tracert 192.168.2.20。验证第一跳是否经过网关接口 IP `192.168.1.1`。

Self-Check Practice Questions 自测练习题

1. Which network device operates at Layer 3 (Network Layer) and routes packets using IP addresses? 哪种网络设备工作在第三层（网络层），并使用 IP 地址路由数据包？

2. What happens to the source/destination MAC addresses when a packet passes through a router? 数据包通过路由器时，源/目的 MAC 地址会发生什么变化？

3. Which device replicates all incoming traffic to all output ports, creating a single collision domain? 哪种设备将所有输入流量复制发送到所有输出端口，从而导致单个共享的冲突域？

4. A Switch splits which domain type to optimize network performance? 交换机划分哪种域以优化网络性能？

5. Identify the official IEEE standard number designated for Wireless Local Area Networks (WLANs). 识别指定用于无线局域网 (WLAN) 的官方 IEEE 标准号。

6. Identify which wireless security protocol provides the highest level of encryption and protection today. 识别如今提供最高级别加密和保护的无线安全协议。

7. Explain how the CSMA/CA protocol prevents collisions in wireless networks. 解释 CSMA/CA 协议如何防止无线网络中的冲突。

8. Describe the primary operational function of an Access Point in wireless LAN networks. 描述接入点 (AP) 在无线局域网中的主要运行功能。

Vocabulary Matching Game 词汇配对游戏

Match the device on the left with its operational Layer of the OSI Model on the right. (Click a term, then click its matching definition). 将左侧的设备与右侧其工作的 OSI 模型层进行配对。（点击术语，然后点击匹配的定义）。

Active Hub
Layer 2 Switch
Network Router
Ethernet NIC
Network Bridge
Operates at Layer 2, filters frames based on MAC address table 工作在数据链路层，通过学习并基于 MAC 地址表有选择地转发数据帧
Hardware containing a unique physical 48-bit MAC address burned-in 包含全球唯一物理烧录的 48 位以太网 MAC 地址的网卡硬件
Operates at Layer 3, routes packets between subnets using IP addresses 工作在网络层，根据目的 IP 逻辑网络地址在各局域子网间路由数据包
Operates at Layer 1, floods incoming electrical signals to all ports 工作在物理层，简单地将输入的电信号广播泛洪转发至其他所有端口
Operates at Layer 2, connects and segments two local LAN sections 工作在数据链路层，连接并根据 MAC 过滤规则隔离两个本地局域网段

Review Questions 复习问答题

Q1. Explain how a network bridge differs from a simple repeater in connecting LAN segments.

Q2. Explain the purpose of the Service Set Identifier (SSID) and discuss how disabling SSID broadcast affects wireless security.

Q3. Describe the purpose and operational benefit of implementing Virtual Local Area Networks (VLANs).

Q4. Describe the function and operational role of a Wireless LAN Controller (WLC) in enterprise networks.

Q5. Design a secure wireless network deployment for a campus, and compare WPA2 and WPA3 protocols.