L13. Compare link state vs distance vector routing.

Question 1

What are link state and distance vector routing?

Answer 1

Link state routing and distance vector routing are two fundamental approaches used in network routing to determine the best path for data packets to travel from a source to a destination.

Question 2

What is the idea of link state routing?

Answer 2

Each router having complete knowledge of the network topology.

Question 3

What is the most common link state routing protocol?

Answer 3

OSPF (Open Shortest Path First)

Question 4

What is the idea of distance vector routing?

Answer 4

Routers sharing their routing tables with immediate neighbors.

Question 5

What is the most common vector routing protocol?

Answer 5

RIP (Routing Information Protocol)

Question 6

How does link state routing work?

Answer 6

1. Each router discovers its neighbors and measures the cost to each directly connected neighbor.
2. Routers generate LSAs (Link State Advertisements), which contain information about the state of the router’s links (e.g., the cost to each neighbor). These LSAs are then flooded throughout the network to all other routers.
3. Each router uses the information from the received LSAs to build a complete map of the network.
4. Routers use the Dijkstra algorithm to compute the shortest path to every other router in the network, updating their routing tables accordingly.

Question 7

What is an LSA?

Answer 7

Link State Advertisement, contains information about the state of the router’s links (e.g., the cost to each neighbor)

Question 8

How are LSAs created?

Answer 8

The router discovers its neighbors and measures the cost to each neighbor.

Question 9

How are LSAs propagated?

Answer 9

LSAs are flooded throughout the network to all routers.

Question 10

How do routers use LSAs?

Answer 10

Each router uses the information from the received LSAs to build a complete map of the network.

Question 11

How do link state routers compute the shortest path to other routers?

Answer 11

Using the Dijkstra algorithm

Question 12

What are the advantages of link state routing?

Answer 12

Scalability, Fast Convergence, and Accurate Metrics

Question 13

Why is link state routing more scalable?

Answer 13

It only sends updates when there are changes in the network, not periodically.

Question 14

Why do link state routed networks converge quickly?

Answer 14

The network converges quickly since each router has a complete map and can independently calculate the shortest path.

Question 15

What is complex about link state routing?

Answer 15

The algorithms and data structures required for link state routing are more complex compared to distance vector routing.

Question 16

What are disadvantages of link state routing?

Answer 16

Complexity, Resource Intensive, Initial Overhead

Question 17

How does link state routing create overhead?

Answer 17

The initial flooding of LSAs can create significant overhead, especially in large networks.

Question 18

Why is link state routing resource intensive?

Answer 18

It requires more CPU and memory resources due to the need to maintain the complete network topology and run the Dijkstra algorithm.

Question 19

How does distance vector routing work?

Answer 19

1. Each router initializes its routing table with direct distances to its neighbors. Distances to all other routers are set to infinity.
2. Periodically, each router sends its routing table to its immediate neighbors.
3. Upon receiving a neighbor’s routing table, a router updates its own routing table based on the Bellman-Ford algorithm, which uses the distance vector formula to compute the shortest path to each destination.
4. The process continues until all routers have consistent routing tables, reflecting the shortest paths to all network destinations.

Question 20

How does a distance vector router initialize its table?

Answer 20

With direct distances to its neighbors. Distances to all other routers are set to infinity.

Question 21

How does routing information propagate in distance vector routed networks?

Answer 21

Each router sends its routing table to its immediate neighbors periodically

Question 22

How does a distance vector router update its table?

Answer 22

Upon receiving a neighbor’s routing table, based on the Bellman-Ford algorithm, which uses the distance vector formula to compute the shortest path to each destination.

Question 23

How does a distance vector routed network converge?

Answer 23

The routers periodically share their tables with other routers and update their own tables upon receiving other routers’ tables using the Bellman-Ford algorithm. The process continues until all routers have consistent routing tables, reflecting the shortest paths to all network destinations.

Question 24

What are the advantages of distance vector routing?

Answer 24

Simplicity, Low Resource Requirements, Easy Configuration

Question 25

How is distance vector routing simpler than link state routing?

Answer 25

The algorithms and data structures used are simpler.

Question 26

Why does distance vector routing require less resources?

Answer 26

It requires less CPU and memory since routers only need to keep track of their neighbors’ distances.

Question 27

What are the disadvantages of distance vector routing?

Answer 27

Slow Convergence, Count-to-Infinity Problem, Periodic Updates

Question 28

Why is slow convergence in distance routing protocols an issue?

Answer 28

It can lead to routing loops and inconsistencies during convergence.

Question 29

How does the count-to-infinity problem arise?

Answer 29

This problem arises when routers continuously increment the distance to a downed node, causing slow convergence and routing issues.

Question 30

What issues can arise from the periodic updates in distance vector routing?

Answer 30

The periodic broadcasting of entire routing tables can create unnecessary network traffic, especially in large networks.

Question 31

Name the four main differences between link state and distance vector routing

Answer 31

1. Link state routing generally converges faster than distance vector routing due to its complete network knowledge and independent shortest path calculations.
2. Link state routing is more scalable for large and complex networks, whereas distance vector routing is better suited for smaller, simpler networks.
3. Link state routing requires more computational and memory resources, while distance vector routing is less resource-intensive.
4. Link state routing protocols are more complex to implement and manage compared to distance vector protocols.

Question 32

What type of networks are link state vs distance vector routing best suited to?

Answer 32

Link state routing, with its fast convergence and scalability, is well-suited for large, dynamic networks, despite its complexity and resource demands. Distance vector routing, on the other hand, offers simplicity and low resource usage, making it ideal for smaller networks.