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Q7(c) · Distance vector versus link state
2024-12-06 · Final 2024-25 / Re-exam 2023-24
Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.
Q7(c). Compare and contrast distance vector and link state routing. Any 5 points each. [5 marks]
Answer
Definition. RIP and OSPF are routing protocols; Bellman–Ford and Dijkstra are algorithms underlying different route-computation approaches.
Simple meaning. Protocol message bhejta hai; algorithm route calculate karta hai.
Understand it step by step
- RIP uses distance-vector information and a bounded hop metric. OSPF distributes link-state information and computes paths using additive costs.
- A generic Bellman–Ford graph exercise can contain negative weights; RIP’s ordinary hop-count metric does not.
- Dijkstra assumes nonnegative edge weights. Do not select it for the negative-weight re-exam graph simply because the question says “routing”.
- State whether a drawn graph is directed or undirected before solving. Both algorithms can be applied to appropriate directed graphs.
| Feature | RIP | OSPF |
|---|---|---|
| Family | Distance vector | Link state |
| Typical metric | Hop count; 16 unreachable | Sum of configured link costs |
| Knowledge exchanged | Destination distances via neighbours | Link-state information |
| Algorithm connection | Distributed Bellman–Ford idea | Dijkstra shortest paths |
| Scale design | Small/simple networks; limited diameter | Area-based scalable design |
Yaad rakho: Distance vector → RIP; link state → OSPF.
Distance vector versus link state: five direct comparisons
| Point | Distance vector | Link state |
|---|---|---|
| Information exchanged | Destination-distance estimates and route information | Descriptions of local links, neighbours and link costs |
| Recipient / distribution | Neighbour-to-neighbour exchange | Flooding across the routing domain or area |
| Topology knowledge | Ordinarily no complete topology map; relies on neighbours' advertised distances | Builds a link-state database representing the area topology |
| Computation | Distributed Bellman–Ford style minimum via neighbours | Dijkstra shortest-path tree from the router itself |
| Convergence / resource tradeoff | Simple advertisements, but failures can cause count-to-infinity and transient loops | More database/computation and flooding overhead; topology changes can be propagated promptly |
RIP and OSPF illustrate these families, respectively. Exact convergence time depends on timers, topology and implementation, so neither family has one universal time bound.