Chapter 15 Connecting LANs, Backbone Networks, and Virtual LANs

Chapter 15 of Data Communications and Networking by Behrouz A. Forouzan, titled "Connecting LANs, Backbone Networks, and Virtual LANs", covers the techniques and devices used to connect multiple local area networks (LANs) together. Below are the detailed notes:

1. Connecting Devices

• Devices that connect different segments of a LAN or multiple LANs are essential in networking.

• There are five categories of connecting devices based on the layer they operate on:

  1. Passive Hubs: Operate below the physical layer; act as a simple connector for multiple LAN branches.

  2. Repeaters: Operate at the physical layer. They regenerate and retransmit signals to extend the range of a network, but they do not filter or route data.

  3. Bridges: Operate at the physical and data link layers, filtering traffic by examining MAC addresses. Bridges prevent unnecessary traffic by forwarding frames only to the destination segment.

  4. Routers: Operate at the physical, data link, and network layers. Routers use IP addresses to forward packets between different networks, making routing decisions based on a routing table.

  5. Gateways: Operate at all layers, converting data between different network architectures or protocols (e.g., OSI to Internet model). They read and interpret messages to forward them.

2. Backbone Networks

• Backbone networks connect multiple LANs to create a larger network.

• Two types of backbone architectures are common:

  1. Bus Backbone: A single cable that connects multiple LANs using bridges. This type of backbone is common in small campus networks.

  2. Star Backbone: A more scalable and efficient architecture where each LAN connects to a central switch (also called a collapsed backbone).

• Connecting Remote LANs: Remote LANs in different geographic locations can be connected through remote bridges, which link the LANs using point-to-point connections such as leased telephone lines.

3. Virtual LANs (VLANs)

• VLANs allow logical grouping of devices within a LAN, even if they are not physically located on the same network segment.

• VLANs are configured using software rather than hardware, enabling flexibility in network management.

• Benefits of VLANs:

  • Security: VLANs can isolate sensitive traffic.

  • Traffic Reduction: VLANs reduce unnecessary broadcast traffic within a network by limiting it to specific VLANs.

  • Simplified Network Management: Network configurations can be altered without changing physical connections.

• Membership in VLANs: Devices can be grouped into VLANs based on characteristics like port numbers, MAC addresses, IP addresses, or multicast addresses.

• Communication between VLANs: When devices in different VLANs need to communicate, routers or Layer 3 switches must be used to route the traffic between VLANs.

4. Advantages of VLANs

• Flexibility: VLANs can be reconfigured without changing physical cabling.

• Cost-Efficiency: VLANs reduce the need for additional hardware and provide a more manageable network structure.

• Improved Security: Broadcast messages are confined to the relevant VLAN, reducing the likelihood of unauthorized access.

5. Summary

• Various types of connecting devices—such as repeaters, bridges, routers, and gateways—are essential for extending, segmenting, and connecting LANs.

• Backbone networks and VLANs offer scalable and flexible solutions for building large and secure networks across multiple locations.

These notes provide a comprehensive overview of the key topics from Chapter 15, including the different connecting devices and how VLANs enhance network flexibility and security【7:1†source】【7:13†source】【7:19†source】.