Distance vector routing (RIP) in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does RIP determine the best route?

In the Routing Information Protocol (RIP), how is the best route to a destination chosen?

A By selecting the route with the fewest hops to the destination

B By choosing the route with the highest bandwidth available

C By selecting the route with the lowest delay time

D By choosing the route with the least number of routers in the network

💡 Hint

Think about what metric RIP uses to measure distance.

RIP uses hop count as its metric. The best route is the one with the fewest hops to the destination.

📋 Factual

intermediate

Maximum hop count in RIP

What is the maximum hop count allowed in RIP before a route is considered unreachable?

A 30 hops

B 10 hops

C 255 hops

D 15 hops

💡 Hint

RIP limits the maximum hop count to prevent routing loops.

RIP defines 15 hops as the maximum distance; anything beyond is unreachable.

🔍 Analysis

advanced

Effect of a link failure in RIP

When a link fails in a RIP network, what mechanism helps prevent routing loops during convergence?

A Distance vector with link-state updates

B Route aggregation

C Split horizon with poison reverse

D Shortest path first algorithm

💡 Hint

Consider how RIP avoids sending routing information back to the source.

Split horizon with poison reverse prevents routing loops by not advertising a route back on the interface it was learned from, marking failed routes with infinite metric.

❓ Comparison

advanced

Difference between RIP and link-state routing

Which of the following correctly contrasts RIP with link-state routing protocols?

A RIP uses hop count as metric and periodic updates; link-state uses a complete map and event-driven updates

B RIP uses bandwidth as metric; link-state uses hop count

C RIP converges faster than link-state protocols

D RIP builds a full network map; link-state only knows neighbors

💡 Hint

Think about how each protocol gathers and shares routing information.

RIP uses hop count and sends updates periodically. Link-state protocols build a full network map and send updates when changes occur.

❓ Reasoning

expert

Why does RIP limit maximum hop count to 15?

Why does the Routing Information Protocol (RIP) set the maximum hop count to 15 instead of a higher number?

A Because routers cannot process more than 15 hops due to hardware limits

B To prevent routing loops by limiting the network size

C To ensure faster convergence by ignoring longer routes

D Because IP addresses are limited to 15 hops in the protocol

💡 Hint

Consider how limiting hop count affects network stability.

Limiting hop count to 15 prevents routing loops and limits the size of networks RIP can support, improving stability.

Practice

1. What is the main metric used by Distance Vector Routing Protocol (RIP) to determine the best path?

easy

A. Hop count

B. Bandwidth

C. Delay

D. Cost

Solution

1. Step 1: Understand RIP metric

   RIP uses hop count as the metric to measure the distance to a destination network.

2. Step 2: Compare with other metrics

   Other protocols may use bandwidth, delay, or cost, but RIP specifically uses hop count.

3. Final Answer:

   Hop count -> Option A

4. Quick Check:

   RIP metric = Hop count [OK]

Hint: RIP counts hops, not speed or delay [OK]

Common Mistakes:

• Confusing hop count with bandwidth
• Thinking RIP uses delay as metric
• Assuming cost is used in RIP

2. Which of the following is the correct way RIP routers share their routing information?

easy

A. Routers send their entire routing table to neighbors periodically

B. Routers send only changed routes immediately

C. Routers broadcast only the best route to each destination

D. Routers send routing updates only when a link fails

Solution

1. Step 1: Recall RIP update method

   RIP routers send their full routing tables to all neighbors at regular intervals.

2. Step 2: Contrast with other methods

   Other protocols may send only changes or triggered updates, but RIP sends full tables periodically.

3. Final Answer:

   Routers send their entire routing table to neighbors periodically -> Option A

4. Quick Check:

   RIP sends full tables periodically [OK]

Hint: RIP sends full tables regularly, not just changes [OK]

Common Mistakes:

• Thinking RIP sends only changed routes
• Assuming RIP uses triggered updates only
• Believing RIP sends partial route info

3. Consider a RIP network where Router A has routes: Network X (2 hops), Network Y (3 hops). Router B receives this info and has Network X (1 hop), Network Y (4 hops). After update, what is Router B's hop count to Network Y?

medium

A. 3 hops

B. 2 hops

C. 5 hops

D. 4 hops

Solution

1. Step 1: Understand RIP update rule

   Router B updates routes by adding 1 hop to neighbors' hop counts.

2. Step 2: Calculate new hop count for Network Y

   Router A reports 3 hops to Network Y, so Router B's new cost is 3 + 1 = 4 hops. But Router B already has 4 hops, so it keeps 4 hops.

3. Step 3: Check if better route exists

   Router B's own route is 4 hops, neighbor's route plus 1 is also 4 hops, so it keeps 4 hops.

4. Final Answer:

   4 hops -> Option D

5. Quick Check:

   Neighbor hops + 1 = 4 hops [OK]

Hint: Add 1 hop to neighbor's count, pick smallest [OK]

Common Mistakes:

• Forgetting to add 1 hop to neighbor's count
• Choosing neighbor's hop count without adding 1
• Ignoring existing route cost

4. A RIP router is not updating its routing table correctly and keeps old routes indefinitely. What is the most likely cause?

medium

A. The router has a maximum hop count set too high

B. The router is using link-state routing instead of distance vector

C. The router is not receiving periodic updates from neighbors

D. The router is sending triggered updates too frequently

Solution

1. Step 1: Identify update mechanism in RIP

   RIP relies on periodic updates from neighbors to refresh routing tables.

2. Step 2: Analyze symptom

   If the router keeps old routes indefinitely, it likely isn't receiving these updates.

3. Final Answer:

   The router is not receiving periodic updates from neighbors -> Option C

4. Quick Check:

   No updates received = stale routes [OK]

Hint: No updates received means routes never refresh [OK]

Common Mistakes:

• Confusing routing protocol type
• Thinking hop count setting causes stale routes
• Assuming triggered updates cause stale routes

5. In a network using RIP, a router receives two routes to the same destination: one with 3 hops via Router X and another with 3 hops via Router Y. Which route will RIP choose and why?

hard

A. The route learned first, because RIP prefers the earliest route

B. Either route, because RIP considers equal hop counts as equal cost

C. The route with the lowest IP address of the next hop router

D. The route with the highest bandwidth link

Solution

1. Step 1: Understand RIP route selection

   RIP selects routes based on hop count; if multiple routes have the same hop count, they are considered equal cost.

2. Step 2: Analyze tie-breaking in RIP

   RIP can load balance across equal-cost routes or pick any; it does not prefer based on IP or bandwidth.

3. Final Answer:

   Either route, because RIP considers equal hop counts as equal cost -> Option B

4. Quick Check:

   Equal hops = equal cost, any route chosen [OK]

Hint: Equal hops mean equal cost; RIP can use either route [OK]

Common Mistakes:

• Assuming RIP prefers first learned route
• Thinking RIP uses next hop IP to decide
• Believing RIP considers bandwidth in route choice