OSPF Protocol Explain? Feature, Routing table, Areas #CCNA

OSPF Protocol Fundamentals
📌 OSPF (Open Shortest Path First) is a Link State Routing Protocol used globally to find the best path between source and destination.
💻 It operates based on the SPF (Shortest Path First) algorithm and utilizes the concept of Trigger Updates, updating only when changes occur in the routing table.
⚙️ Developed by IETF, OSPF is an Open Standard Protocol, a successor to RIP, and operates as a Classless Routing Protocol.

OSPF Metrics and Communication
🔢 The Administrative Distance (AD) value for OSPF is 110.
📈 The metric used is equivalent to Cost, calculated by the formula $10^8$ / Bandwidth (in bits per second).
✉️ OSPF routers send Hello Packets every 10 seconds to neighbors and communicate updates via Multicast address 224.0.0.5.
🗺️ It creates a hierarchical design with multiple areas, where Area Zero is designated as the Backbone Area.

Router ID and OSPF Tables
🆔 The Router ID is critical and is determined by the highest IP address of an active physical interface on the router.
💡 If a Logical Interface is configured, its IP address will always take precedence over physical interface IPs in determining the Router ID.
📋 OSPF maintains three essential tables: the Neighbor Table (information about directly connected neighbors), the Database Table (contains the entire topology view/LSAs), and the Routing Information Table (stores the best paths calculated by the SPF algorithm).

Disadvantages and Dynamic Updates
📉 A key disadvantage is that OSPF consumes more memory and CPU processing due to maintaining multiple tables and complex tasks, making it suitable for large networks.
🔗 When a link goes down, the corresponding entries in the Neighbor, Database, and Routing Information Tables are canceled or held, triggering the SPF algorithm to recalculate and establish a new best path (e.g., rerouting through Area Zero/Backbone).

Key Points & Insights
➡️ OSPF is a Link State Protocol that utilizes the SPF algorithm to determine the most efficient route based on Cost (inverse of bandwidth).
➡️ The protocol uses Trigger Updates, meaning it only sends updates when a change is detected, unlike Distance Vector protocols that update periodically.
➡️ Understanding the three tables (Neighbor, Database, Routing) is crucial for comprehending how OSPF maintains a consistent, recalculated topology view upon link failures.

📸 Video summarized with SummaryTube.com on Feb 02, 2026, 02:26 UTC