Networking Chapter 4: Interconnecting LANs

Chapter 4: Interconnecting LANs

• This chapter introduces concepts and issues related to connecting local area networks (LANs).
• Similar concepts apply to connecting LANs in campus networks or wide area networks (WANs).
• A campus network is a collection of two or more interconnected LANs, potentially within or across multiple buildings.

Chapter Outline

• Introduction
• Hubs
• Network Bridges
• Network Switches
• Routers
• Interconnecting LANs with the Router
• Configuring Network Interface - Auto-negotiation

Chapter Objectives

• Describe hub, bridge, and switch functions in interconnecting LANs.
• Compare the advantages of a switch over a hub.
• Explain how a router interconnects LANs.
• Identify the router interface components.
• Define and illustrate the concept of auto-negotiation.
• Define the concept of a network segment.
• Define the function of a gateway in a computer network.

Introduction

• The utility of LANs led users to desire connecting multiple networks.
• This chapter, along with subsequent ones, aims to detail the related concepts and issues associated with interconnecting LANs.

The Network Hub

• A hub is a fundamental networking device that connects multiple computers or network devices.
• It's a physical layer (layer 1) device with limited intelligence.
• It operates using a simple broadcast mechanism.
• Network bandwidth is shared among connected devices.

The Network Bridge

• A bridge is a layer 2 device in the OSI model linking two LANs or network segments.
• It uses Media Access Control (MAC) addresses to forward data packets between adjacent segments.
• It restricts data traffic to only the necessary packets needed between the connected segments..

Bridging Table

• Bridges use a bridging table of MAC addresses for the connected hosts and their interfaces.
• This table helps the bridge determine where to forward data packets based on the destination MAC address.
• When a host sends a data packet, the bridge records the source MAC address and the port where it originated. This creates a record required to build the bridging table, or the MAC address table.

Address Resolution Protocol (ARP)

• Networking devices (e.g., computers) contain an ARP cache.
• This cache, also called the ARP table, temporarily stores MAC addresses of recently contacted hosts.
• The ARP cache allows for direct transmission of messages to the destination device's MAC address without unnecessary ARP requests.
• The ARP cache can be examined in Windows using the arp -a command within the command prompt.

The Network Switch

• Switches operate at layer 2 (data link layer) of the OSI model, acting like intelligent multiport bridges.
• MAC addresses are used to direct data packets to specific destination ports.
• Supports different communication types including; unicast, multicast, broadcast.
• Switches improve performance by reducing network congestion compared to hubs by enabling simultaneous data transmission across multiple connections.

Types of Switches

• Unmanaged switches are inexpensive and readily set up in home or small business networks.
• Managed switches are adaptable for complex networks in organizations, providing more customization and control options over network functions.

Network Switch: Verifying the Link Light

• Link lights visually verify proper network connection alignment between network devices.
• The presence of a link light indicates that the devices are communicating successfully.
• A missing link light indicates either cabling or hardware issues.

L2 Network Switch

• The system uses a star topology.
• Data transmission between devices is optimized because the switch establishes a direct connection for specific pairs of devices.
• Simultaneous communication between different devices is allowed because the device connections are independent.

Switch Benefits

• Reduced network congestion.
• Faster data transfers.
• Increased manageability

Content Addressable Memory (CAM)

• CAM is a high-speed memory used in switches to store mapping information for MAC addresses, enabling quick data routing.
• The switch processes MAC addresses for incoming data packets and immediately redirects them to appropriate ports based on the stored MAC address information.

Static vs. Dynamic MAC

• Dynamic MAC addresses are assigned automatically to a port on a switch when a device is connected.
• Static MAC assignments provide permanent MAC addresses and prevent their associated port configurations from expiring.
• Security features associated with a switch's ports can be configured to prevent unauthorized MAC addresses from using specific network ports.

MAC Aging Time

• The system defines an aging time for MAC addresses to allow for an inactivity period between device sessions; commonly 300 seconds.
• After this inactivity time, the switch removes the MAC address and associated port entry from the switch's table (to conserve memory storage).
• The counter for the aging time restarts when data activity resumes from the device initiating the communication.

Switching Modes

• Store-and-Forward: The entire data frame is received before any forwarding decisions take place. It offers error checking before delivery to the destination. However, latency (delay) is longer, especially with large packets.

• Cut-Through: Data packets are forwarded once the destination MAC address is recognized. Offers lower latency, but lacks error checking, which can generate faulty data packets. This method comes in two varieties including; Fast-Forward and Fragment-Free.

  • Fast-Forward: Offers the lowest latency possible because forwarding decisions are made as soon as the required data is available.
  • Fragment-Free: Filters out smaller packets; less than 64 bytes because Ethernet data packets must be minimum 64 bytes, and any smaller packet is therefore considered a fragmentation collision.

Assembling an Office LAN

• Follow these steps to assemble a basic office LAN.
  1. Document all devices to be linked, and then draw out the required network diagram, including all devices, MAC and IP addresses in the diagram.
  2. Connect the assembled devices using the correct cabling configuration.
  3. Configure each device's IP addresses according to the prepared network diagram.

LAN Documentation

• Maintain detailed documentation of all IP and MAC addresses to ensure successful network management.
• Use the ipconfig /all command in Windows XP to obtain MAC addresses.

The Router

• Routers function at layer 3 (network layer) of the OSI model, directing data packets by inspecting network addresses rather than physical MAC addresses.

Router Interface Components

• USB (Universal Serial Bus)
• Console
• Auxiliary
• Voice Interface
• FXS/DID (Foreign Exchange Station/Direct Inward Dialing)
• FastEthernet
• Serial
• Modem

Interconnecting LANs with the Router

• Routers connect various LAN segments within a campus or across a wider geographical region, like a country or around the world.
• Routers can handle network communications where multiple protocols may be used (e.g., Ethernet, Token Ring)

Routers - Review

• Data routing occurs based on network addresses.
• Routers and layer 2 switches offer different types of information exchange, where switches work with MAC addressing and routers work with IP addressing.

Router Functionality

• The Router A sends data to Router C through the use of a segmented network in this example configuration.

Gateway Address

• Gateway Address: The address of the device that connects a LAN to another network outside the LAN This address is used by hosts to route data packets to external devices. The gateway address for this simplified example is 10.10.20.250

Network Segment

• A network segment is a section of a network where data traffic originating from a specific component of the network does not affect other sections of the network.
• A segment is defined by an internetworking device (router, hub, switch) connection between interconnected LANs

Explore the key concepts of interconnecting local area networks (LANs) in Chapter 4. This chapter covers the functionality and advantages of hubs, bridges, switches, and routers, along with the essential practice of auto-negotiation for network interfaces. Understand how to create efficient campus networks by effectively connecting multiple LANs.