Day 9: Fault Tolerance and Redundancy

Learning Objectives

• CSN-1.E: For fault-tolerant systems like the Internet: a. Describe the benefits of fault tolerance. b. Explain how a given system is fault-tolerant. c. Identify vulnerabilities to failure in a system.

Essential Questions

• How is the Internet designed to be fault-tolerant?
• What role does redundancy play in network reliability?
• How do systems recover from failures?

Materials Needed

• Presentation slides on fault tolerance and redundancy
• Network simulation software
• Fault tolerance scenario cards
• Network design templates
• Exit ticket templates

Vocabulary

• Fault tolerance
• Redundancy
• Single point of failure
• Failover
• Load balancing
• Replication
• Backup
• Disaster recovery
• High availability
• Resilience

Procedure (50 minutes)

Opening (8 minutes)

1. Review and Connection (3 minutes)

   • Review Internet protocols from previous lesson
   • Connect to today's focus on how the Internet maintains reliability

2. Warm-up Activity (5 minutes)

   • Present a simple network diagram
   • Ask students to identify what would happen if specific components failed
   • Discuss the concept of "single points of failure"
   • Introduce the need for fault tolerance and redundancy

Main Activities (32 minutes)

3. Lecture: Network Reliability and Fault Tolerance (12 minutes)

   • Define fault tolerance as the ability to continue functioning when components fail
   • Explain key concepts:
     • Redundancy: Including extra components to mitigate failures
     • Multiple paths: More than one route between devices
     • Dynamic routing: Adapting to network changes
     • Distributed systems: No single point of failure
   • Discuss how the Internet was designed for fault tolerance:
     • Decentralized architecture
     • Packet switching allows rerouting
     • Redundant connections between networks
     • Distributed DNS system
   • Explain common fault tolerance strategies:
     • Hardware redundancy (duplicate components)
     • Data redundancy (backups, replication)
     • Geographic redundancy (multiple locations)
     • Service redundancy (multiple providers)
   • Discuss the trade-offs of redundancy (cost vs. reliability)

4. Demonstration: Redundant Paths and Systems (8 minutes)

   • Use network simulation to show how data finds alternate paths when links fail
   • Demonstrate how redundant systems take over when primary systems fail
   • Show examples of real-world redundancy:
     • Multiple internet connections
     • Server clusters
     • RAID storage systems
     • Content delivery networks
   • Illustrate how redundancy improves reliability but increases complexity and cost

5. Activity: Designing a Fault-Tolerant Network (12 minutes)

   • Divide class into small groups
   • Provide each group with a network design scenario
   • Groups design a fault-tolerant network that:
     • Eliminates single points of failure
     • Includes redundant connections
     • Provides backup systems
     • Can recover from multiple simultaneous failures
   • Groups identify potential vulnerabilities in their designs
   • Groups share their designs and explain their fault tolerance strategies

Closing (10 minutes)

6. Discussion: Real-World Network Failures and Recoveries (5 minutes)

   • Lead a discussion on notable network/internet outages
   • Analyze how redundancy helped or could have helped in these situations
   • Discuss the balance between cost and reliability
   • Address any misconceptions about network resilience
   • Emphasize that fault tolerance is about managing failures, not eliminating them

7. Exit Ticket: Fault-Tolerant Design (5 minutes)

   • Present students with a network scenario
   • Students design a fault-tolerant solution
   • Students identify potential vulnerabilities
   • Students explain how their design handles specific failure scenarios
   • Collect responses before students leave

Assessment

• Formative: Quality of fault-tolerant network design
• Exit Ticket: Appropriateness of fault-tolerant solution

Differentiation

For Advanced Students

• Ask them to design solutions for more complex failure scenarios
• Have them calculate reliability metrics for different designs
• Challenge them to consider cost-benefit analysis of redundancy

For Struggling Students

• Provide more structured templates for network design
• Focus on simpler redundancy concepts
• Use more visual aids and concrete examples

Homework/Extension

• Research a major internet or service outage and analyze the failure points
• Design a fault-tolerant home or small business network
• Create an infographic explaining fault tolerance concepts

Teacher Notes

• Use analogies to help students understand redundancy (e.g., multiple routes to school)
• Be prepared to address questions about specific fault tolerance technologies
• Make connections to students' experiences with service outages
• Consider discussing how fault tolerance applies beyond networks (e.g., space systems)
• Emphasize that understanding fault tolerance helps with designing reliable systems