Jeremy’s IT Lab: CCNA OSPF Lecture

Introduction

• Continuation of OSPF studies for CCNA
• Recap of OSPF basics from Part 1
• Topics covered:
  • OSPF Metric (Cost)
  • OSPF Neighbors
  • Additional OSPF Configurations
• Bonus question from Boson ExSim (CCNA practice exams)

OSPF Metric: Cost

• Definition: OSPF's metric is called 'cost.'
• Calculation:
  • Based on interface bandwidth
  • Default reference bandwidth: 100 Mbps
  • Formula: Reference Bandwidth / Interface Bandwidth
• Examples:
  • Ethernet (10 Mbps): Cost = 10
  • FastEthernet (100 Mbps): Cost = 1
  • Gigabit Ethernet (1000 Mbps) and above: Cost = 1 (due to conversion of values <1 to 1)
• Modifying Cost:
  • Change reference bandwidth using AUTO-COST REFERENCE-BANDWIDTH
  • Manually configure cost with IP OSPF COST
  • Change interface bandwidth (not recommended for OSPF cost change)
• Command Details:
  • AUTO-COST REFERENCE-BANDWIDTH in OSPF config mode
  • BANDWIDTH command for interface bandwidth (entered in kbps)

OSPF Neighbors

• Importance of configuring OSPF neighbors
• Hello Packets:
  • Sent every 10 seconds (default hello timer)
  • Multicast address: 224.0.0.5
• Neighbor States:
  1. Down: No knowledge of neighbor
  2. Init: Hello packet received, but no acknowledgment
  3. 2-way: Bidirectional communication established
  4. Exstart: Master/Slave roles decided
  5. Exchange: Exchange DBD packets
  6. Loading: Request and receive LSAs
  7. Full: Full adjacency with synchronized LSDBs
• Timers:
  • Dead timer: 40 seconds
• Show Commands:
  • SHOW IP OSPF NEIGHBOR
  • SHOW IP OSPF INTERFACE

Additional OSPF Configurations

• Passive Interfaces:
  • Default passive with PASSIVE-INTERFACE DEFAULT
  • Override with NO PASSIVE-INTERFACE
• Activating OSPF on Interfaces:
  • IP OSPF <process ID> AREA <area ID> from interface config mode

Summary

• OSPF Cost Calculation: Reference bandwidth / interface bandwidth
• Neighbor Formation: Importance of neighbor states and hello/dead timers
• Configuring OSPF: Directly on interfaces and passive interface configuration

Quiz Questions Review

1. Order of OSPF neighbor states
2. Correct statement about OSPF's default cost
3. State where Master/Slave roles are decided
4. Command to achieve specific OSPF cost on FastEthernet
5. Default OSPF Hello/Dead timers for Ethernet

Boson ExSim Bonus Question

• Practical application of reference bandwidth settings
• Importance of choosing routes based on cost

Closing

• Invitation to subscribe, like, comment, and share
• Mention of supplementary materials: Anki flashcards, packet tracer lab
• Acknowledgment of JCNP-level channel supporters
• Encouragement to check out Boson ExSim for practice exams