OSPF Routing Protocol Questions and Answers
1. What is OSPF Routing Protocol?
Answer:
OSPF (Open Shortest Path First) is a link-state routing protocol that uses the SPF (Shortest Path First) algorithm, developed by Dijkstra, to calculate the shortest path. This best path is added to the routing table, allowing efficient routing decisions.
2. How can we change the router ID in the OSPF domain?
Answer:
To change the OSPF Router ID:
Use the command: #clear ip ospf process.
Alternatively, reload the IOS. This will reset OSPF and apply the new Router ID.
3. What are the important features of OSPF?
Answer:
Operates at the network layer (Protocol number: 89).
Provides routing data in the TCP/IP model.
Uses multicast addresses 224.0.0.5 (All SPF Routers) and 224.0.0.6 (Designated Routers).
More efficient than RIP as it sends less traffic.
Uses the SPF algorithm for optimal path selection.
4. What are the key attributes of OSPF?
Answer:
Equal Cost Routes Management: CEF Load Balancing.
Protocol Type: Link-State Protocol.
Transport: Uses IP (Protocol number: 89).
Metric: Based on cost (inversely proportional to bandwidth).
Standards: OSPFv2 (RFC 2328) for IPv4 and OSPFv3 (RFC 2740) for IPv6.
5. How does OSPF work?
Answer:
OSPF routers exchange routing updates using LSAs (Link-State Advertisements).
Changes are propagated to a Link-State Database (LSDB).
Routers run the SPF algorithm to calculate the shortest path.
Only changes in the topology are sent, reducing bandwidth usage.
Updated routing tables ensure the best path is selected for data transfer.
6. Name different types of OSPF LSAs.
Answer:
Type 1 (Router LSA): Describes a router's links within an area.
Type 2 (Network LSA): Created by the DR to describe routers on the same segment.
Type 3 (Summary LSA): Generated by ABRs for inter-area routes.
Type 4 (Summary ASBR LSA): Describes routes to ASBRs.
Type 5 (External LSA): Describes external routes injected by ASBRs.
Type 7 (NSSA LSA): Generated in NSSA areas for external routes.
7. What are the different functions and workings of OSPF?
Answer:
Neighbor Discovery: Uses Hello packets to form adjacencies.
LSA Exchange: Routers exchange topology data via LSAs.
LSDB Maintenance: Builds a topology map of the entire network.
SPF Algorithm: Calculates shortest paths using Dijkstra's algorithm.
Routing Table Update: Updates routes after running SPF.
Hierarchical Design: Divides large networks into areas for scalability.
Efficient Updates: Sends only changes, reducing bandwidth usage.
8. What are the advantages of dividing the network into areas?
Answer:
Limits network instability to specific areas.
Reduces routing overhead.
Improves convergence speed.
9. What is OSPF Hello and Dead Interval?
Answer:
Hello Interval: Time between Hello packets sent by an OSPF router (default is 10 seconds for point-to-point links).
Dead Interval: Time for a neighbor to be declared inactive if no Hello packets are received (default is 4 times the Hello interval).
10. What is DR and BDR in OSPF?
Answer:
DR (Designated Router): Manages LSAs for the segment and serves as a central point for routing updates.
BDR (Backup Designated Router): Takes over if the DR fails.
Multicast Addresses:
DR uses 224.0.0.5 to receive updates.
BDR listens to 224.0.0.6.
Let me know if you'd like additional details or further questions!