Two-Node Loop Instability

Duration: 6 min

This video lesson is available to enrolled students.

Return to /learn/COMPUTER-SCIENCE/computer-networks/net-layerrouting-protocol/dvr-rip-split-horizon/asset-two-node-loop-instability after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. DBMS: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Decomposition Properties & 4NF, Normalization (1NF - BCNF), File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, ORDBMS, Database Security & Authorization, Query Processing & Optimization, Enhanced Data Models, Data Warehousing & Mining, Big Data Systems, NoSQL
  2. SQL: SQL
  3. Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Windows OS, Linux OS, Security, Distributed Systems, Virtual Machines
  4. Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  5. Computer Networks: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security, Mobile Technology, Cloud Computing and IoT, Cyber and Info Security
  6. MS Office & Basics of Computer: MS Office by Yash Sir
  7. Cloud Computing: Emerging Tech Trends
  8. R Programming Language: R Programming Language
  9. Tableau: Tableau
  10. Live Class Notes: Placement Live Classes
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture introduces two-node loop instability in distance-vector routing, explaining why a broken link (cost infinity) is not recognized immediately because the algorithm reports minimum costs first. The instructor uses a five-panel diagram of nodes A and B reaching node X to show how asynchronous table exchanges cause the cost to reach X to increase gradually until infinity, a problem called count-to-infinity.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The slide titled "Two-Node Loop Instability" states that if a link is broken (cost becomes infinity), every other router should be aware immediately, but distance-vector routing takes time because the algorithm reports the minimum first. The instructor introduces a network diagram with nodes and arrows to visualize how routers can incorrectly route traffic back and forth, naming the issue "count to infinity."

  2. 2:00 – 5:00 02:00-05:00

    The lecture walks through a two-node example with A and B connected to X. On-screen text says "Initially in fig.(a) nodes A and B know how to reach node X," then the link between A and B fails. If A sends its table immediately, everything is fine; instability occurs if B sends its forwarding table to A first. Node A assumes B found a path to X and updates, then B does the same, so "The cost of reaching X increases gradually until it reaches infinity." Panels a–e show tables before failure, after link failure, after A is updated by B, after B is updated by A, and finally.

  3. 5:00 – 5:38 05:00-05:38

    The instructor continues emphasizing the five-panel diagram, with red hand-drawn circles and crosses marking changing table entries such as around "1/3/A" and a crossed-out X. The final point is that at the moment the cost reaches infinity, both A and B know X cannot be reached. The slide reiterates that the cost of reaching X increases gradually until it reaches infinity.

The central idea is that distance-vector routing's reliance on minimum-cost reporting creates a delay in propagating link failures, producing count-to-infinity. The worked example uses nodes A and B reaching X: before failure both know a path; after the A-B link fails, asynchronous updates make each node believe the other has a valid route. Each update increases the recorded cost step by step until infinity, at which point both nodes recognize X is unreachable. The five-panel sequence (a–e) and red annotations on table values are the key evidence for this progression.

Loading lesson…