Computer Networks · TEE · papers
Q4(b) · RIP route updates
2025-02-19 · 2023-24 / 2024-25
Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.
Q4(b). Explain Routing Information Protocol. Illustrate with an example how routes are updated in RIP. [10 marks]
Answer
Definition. Routing Information Protocol (RIP) is an interior distance-vector routing protocol that uses a bounded metric, commonly hop count, to select routes.
Simple meaning. RIP mein hops count; 15 tak reachable, 16 means unreachable.
Understand it step by step
- RIPv2 uses distance-vector updates and carries subnet-mask information, allowing classless routes.
- The usual hop-count metric admits costs 1–15 for reachable routes; 16 denotes infinity/unreachable. A received advertisement is incremented by the local link cost and capped at 16.
- RIPv2 normally sends periodic updates about every 30 seconds, with implementation/timer behavior and triggered updates affecting the exact timing. RIPv2 uses UDP port 520 and can send updates to multicast 224.0.0.9.
- Hop count does not directly measure bandwidth or delay, so a low-hop route is not always the fastest link path. The 15-hop limit restricts scale.
RIP uses distance-vector routing and commonly hop count as its metric. Reachable metrics are at most 15; 16 represents infinity. Its main limitations include limited diameter, a coarse metric and relatively slow convergence with possible temporary loops.
Yaad rakho: RIP: neighbour distances; 16 is infinity.
Route-update example using RIP hop counts
Let router A have neighbours B and C, each one hop away. B advertises destination network N at 2 hops; C advertises N at 4 hops. A adds its local one-hop cost to each advertisement.
| Candidate | Calculation | Result |
|---|---|---|
| Via B | 1 + 2 | 3 hops |
| Via C | 1 + 4 | 5 hops |
A chooses B and records (destination N, next hop B, metric 3). If B subsequently advertises metric 16, that route is unreachable. If the advertisement from C is still valid, A can select C at metric 5 instead. Updates can propagate to other routers; split horizon/poisoned reverse and triggered updates help limit loops and speed convergence, but do not make every transient loop impossible.