Distance vector routing (RIP) in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Distance Vector Routing Protocol (RIP)?

RIP is a simple routing protocol that helps routers find the best path to send data by sharing information about the distance (number of hops) to other networks.

beginner

How does RIP measure the distance to a destination?

RIP counts the number of hops (routers) between the source and the destination. The path with the fewest hops is chosen as the best route.

intermediate

What is the maximum hop count allowed in RIP?

The maximum hop count in RIP is 15. Any destination more than 15 hops away is considered unreachable.

intermediate

How often does RIP update its routing table?

RIP routers send updates every 30 seconds to share their routing tables with neighbors, helping keep routes current.

advanced

What problem does the 'count to infinity' issue in RIP refer to?

It is a problem where routers keep increasing the hop count for a failed route endlessly, causing slow convergence and routing loops.

What metric does RIP use to select the best route?

A Bandwidth

B Cost

C Delay

D Number of hops

RIP uses the number of hops (routers) as the metric to choose the best path.

What is the maximum number of hops allowed in RIP before a destination is considered unreachable?

A 10

B 30

C 15

D 20

RIP considers any route with more than 15 hops as unreachable.

How often does RIP send routing updates to its neighbors?

A Every 10 seconds

B Every 30 seconds

C Every 60 seconds

D Only when topology changes

RIP sends updates every 30 seconds to keep routing information fresh.

Which problem is common in RIP due to slow convergence?

A Routing loops

B Packet loss

C IP address conflicts

D DNS failure

Routing loops can happen in RIP because of slow updates and the count to infinity problem.

RIP is classified as which type of routing protocol?

A Distance vector

B Link-state

C Path vector

D Hybrid

RIP is a distance vector routing protocol because it uses distance (hop count) vectors to find routes.

Explain how RIP determines the best path to a destination and what limits it has.

Think about how RIP counts routers and how it shares this info.

Describe the 'count to infinity' problem in RIP and why it affects network routing.

Consider what happens when a route fails and routers keep increasing hop counts.

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