Lecture 3 - Switches and Routers - 2025
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Course Details:
Title: Network Essentials
Lecture 3: Switches & Routers
Instructor: Dr. Jiankang Zhang
Contact: jzhang3@bournemouth.ac.uk
Location: Room P316
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Linking Networks
Networks are interconnected through switches and routers.
Networks Visualization:
Network A, B, C, and D
Packet Travel: How packets move between networks.
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Definition of a Switch:
Basics of network switching.
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Network Switch Introduction:
Examples: Cisco 2960, Netgear
Connection Setup:
Connect a PC to the switch with a network cable.
Function:
Basic building block of Local Area Networks (LANs)
Connects different parts of the network and devices.
Ports typically include 24 or 48 sockets on models like Cisco 2960.
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Switch Functionality:
Network Creation:
Establishes a local network (LAN).
Connectivity:
Devices can connect to the network.
Port Characteristics:
Number of ports usually a multiple of 4.
Provides dedicated bandwidth for each port.
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Data Handling by Switches:
Forwards data packets from source to destination port.
Allows multiple simultaneous communications between port pairs.
Pre-Forwarding: Can start forwarding packets before fully receiving them.
Maintains an internal look-up table for ports and node addresses.
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Port to Port Delivery:
Switch ports facilitate virtual connections only during data transfers.
Only the destination device's port receives the data frame.
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Switch Functions Overview:
Performs four main actions using a look-up table:
Learn: Identify connected devices.
Filter: Determine which packets to keep or discard.
Forward: Send packets to correct destination.
Flood: Send packets to all ports if destination is unknown.
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Switched Network Architecture Example:
Demonstrates sending messages from Host A to Host D via a switch.
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Types of Switches by Manageability:
Managed Switches:
Configurable, suited for Virtual LANs.
Operate at Layer 2 or Layer 3 of the OSI model.
Unmanaged Switches:
Basic functionality with no configuration options.
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Unmanaged Switches Overview:
Examples of NETGEAR switches.
Various types include Smart Cloud Switches and Multi-Gig Switches.
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Layer 2 and Layer 3 Switches:
Layer 2: Handles MAC addresses.
Layer 3: Combines router and switch functionalities; handles both MAC and IP addresses but is less functional than routers.
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Switch Operations Types:
Cut Through Processing:
Fast; forwards packets after reading the destination address.
Stored-and-Forward Processing:
Slower; forwards packets after checking for errors.
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Network Expansion:
Additional switches can be connected via crossover cables or specialized cables.
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Comparison: Switches vs. Routers:
Switches: Create LANs.
Routers: Connect different networks.
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Function of Routers:
Connect two or more networks.
Each network must have its own unique network ID.
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Router Characteristics:
Divides networks while resembling a switch.
More expensive and requires configuration unlike switches.
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Routers vs. Switches Visual:
Diagram showing connections among PCs and switches.
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Routing Network IDs:
Each router port requires a different network ID, akin to street names distinguishing roadways at roundabouts.
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Exercise 1 - IP Address Allocation:
Task: Allocate Class C IP addresses for provided network configuration.
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Exercise 1 - Answer:
Switch ports do not require IP addresses.
Sample assignments of IP addresses based on exercise setup.
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Default Gateway/Router Concept:
Addresses outside the network sent to the default gateway, configured for each computer.
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Default Gateway Illustration:
Diagram explaining how devices know local from external networks through the default gateway.
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Complex Network Routers:
Routers can serve as default gateways for other routers, configured using routing algorithms.
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Default Gateway Setup:
Details regarding configurations of default gateways for multiple computers on different networks.
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Routers with Multiple Gateways:
Routers may act as gateways for other routers, utilizing routing algorithms for optimal path selection.
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Grouping by Location:
Visual representation of devices grouped by their physical office locations.
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Grouping by Purpose:
Departments grouped based on their operational functions.
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Grouping by Ownership:
Shows various locations managed by distinct IT services or teams.
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Grouping by Security Considerations:
Different areas within a network address varied security needs.
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IP Configuration Command:
Command: ipconfig to find default router and network configurations.
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Router Routing Table Details:
Contains network information and updates frequently with route changes communicated among routers.
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Routing Table Entry Components:
Descriptions of fields such as Network ID, Subnet Mask, Next Hop, Outgoing Interface, and Metric.
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Example Routing Table:
Sample routing table showing destination networks and associated metrics.
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Routing Tables in Routers:
Illustration of different networks and their next-hop addresses.
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Static Routing in Routers:
Addresses manually entered into routing tables for fixed paths between networks.
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Dynamic Routing Tables in Routers:
Networks learn about routes through interactions with other routers to establish paths.
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Resilient Network Properties:
Defines how routers use routing tables for alternative routes if a primary path fails.
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Packet Journey:
Discusses journey of data packets through various routers until reaching the destination.
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Diverse Routing Paths:
Explanation of how packets may take different routes leading to varying delays, particularly in applications like online gaming.
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Routing Step 1:
Initial packet sent to the nearest router by the originating computer.
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Routing Step 2:
Router examines the packet IP header upon receipt.
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Routing Step 3:
Utilizes a forwarding table for packet routing decisions based on destination address.
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Routing Step 4:
Final router forwards the packet to the destination based on forwarding decisions.
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Routing Decision Criteria:
Longest Prefix Match: Selects routes by longest match.
Administrative Distance: Chooses routes with lower administrative distance.
Metric: Uses metric values for route selection.
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Switches vs Routers Comparison:
Performance: Switches generally faster and cheaper than routers.
Operation Levels: Different OSI model layers; switches operate at Layer 2, routers at Layer 3.
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Detailed Comparison Overview:
Differences in functionality, configurations, and operational speeds between switches and routers.
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Summary of Key Points:
Functions of switches and routers, types of switches, and routing tables.
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Exercise 2:
Task: Allocate IP addresses and gateways for devices across different networks.
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Exercise 2 - Answer Overview:
Presents an example solution with assigned network IDs and gateways.
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Q&A Session:
Invitation for questions and clarifications on the material.