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Distance Vector Routing
Distributed routing algorithm using Bellman-Ford principle
Algorithm Type
Distributed, iterative, asynchronous
Convergence
Eventually converges to shortest paths
Used By
RIP (Routing Information Protocol)
Distance Vector Simulation
Iteration: 0
Routing Tables
Node A
| Dest | Dist | Next |
|---|---|---|
| A | 0 | - |
| B | 0 | - |
| C | 0 | - |
| D | 0 | - |
Node B
| Dest | Dist | Next |
|---|---|---|
| A | 0 | - |
| B | 0 | - |
| C | 0 | - |
| D | 0 | - |
Node C
| Dest | Dist | Next |
|---|---|---|
| A | 0 | - |
| B | 0 | - |
| C | 0 | - |
| D | 0 | - |
Node D
| Dest | Dist | Next |
|---|---|---|
| A | 0 | - |
| B | 0 | - |
| C | 0 | - |
| D | 0 | - |
Algorithm Explanation
Bellman-Ford Equation
dx(y) = minv { c(x,v) + dv(y) }
Distance from x to y = minimum over all neighbors v of (cost to v + distance from v to y)
Advantages
- • Simple to implement and understand
- • Distributed algorithm - no central authority
- • Self-correcting and adaptive
- • Handles network changes automatically
- • Low computational overhead per node
Disadvantages
- • Count-to-infinity problem
- • Slow convergence in large networks
- • Routing loops during convergence
- • Poor performance with link failures
- • Limited scalability (hop count limit)
Algorithm Steps
1. Initialize: Each node knows distance to direct neighbors
2. Exchange: Nodes periodically send their distance vectors to neighbors
3. Update: Upon receiving a distance vector, update own table using Bellman-Ford equation
4. Repeat: Continue until no more updates occur (convergence)
📝 Exam Preparation Tips
Key Points to Remember
- • Based on Bellman-Ford algorithm
- • Each node maintains distance vector to all destinations
- • Routing updates sent to immediate neighbors only
- • Uses hop count as metric (RIP limitation: 15 hops)
- • Count-to-infinity solved by split horizon, poison reverse
Common Exam Questions
- • "Trace distance vector algorithm execution" (10 marks)
- • "Compare distance vector vs link state" (8 marks)
- • "Explain count-to-infinity problem" (6 marks)
- • "Calculate routing table after topology change" (8 marks)
- • "Advantages and disadvantages of DV routing" (6 marks)