RIP (Routing Information Protocol) - Conceptual Overview
🔹 What is RIP?
RIP is one of the oldest distance vector routing protocols used in IP networks. It enables routers to exchange network topology information to determine the best route to a destination.
🕰️ Historical Background
- RIP v1: Introduced in the 1980s (RFC 1058). Classful, no support for VLSM or subnet info in updates.
- RIP v2: Introduced in 1994 (RFC 2453). Classless, supports VLSM, CIDR, and authentication.
📦 RIP as a Distance Vector Protocol
- Routing by Rumor: Routers learn routes indirectly from neighbors' routing tables.
- Hop Count as Metric: 1 hop = directly connected, 2 hops = one router away, and so on.
- Maximum Hop Count: Limited to 15. 16 is considered unreachable.
Example: If Router A is connected to Router B (1 hop), and B to C (2 hops from A), A cannot reach beyond 15 routers.
🔄 Periodic Updates
RIP sends its full routing table to neighbors every 30 seconds, which can consume bandwidth in larger networks.
⚠️ Routing Table Convergence
- Slow Convergence: May take up to 180 seconds to detect changes.
- Count-to-Infinity: Hop count may increase indefinitely when a route fails, until 16 is reached.
🧠 Loop Prevention Techniques
- Split Horizon: Prevents a router from advertising a route back out the interface it came in.
- Route Poisoning: Sets hop count to 16 to mark routes as unreachable.
- Poison Reverse: Confirms route poisoning by advertising unreachable routes back to sender.
⏱️ Timers in RIP
| Timer | Purpose | Default Value |
|---|---|---|
| Update Timer | Time between regular updates | 30 sec |
| Invalid Timer | Route marked invalid if not updated | 180 sec |
| Hold-down Timer | Wait for better route after failure | 180 sec |
| Flush Timer | Route removed from table | 240 sec |
🔀 RIP Version Differences
| Feature | RIP v1 | RIP v2 |
|---|---|---|
| Classless Routing | ❌ No | ✅ Yes |
| VLSM Support | ❌ No | ✅ Yes |
| Subnet Mask in Updates | ❌ No | ✅ Yes |
| Authentication | ❌ No | ✅ Yes (Plain or MD5) |
📉 Limitations of RIP
- Scalability: Not suitable for large networks due to 15-hop limit.
- Bandwidth Usage: Wastes bandwidth due to frequent full-table updates.
- Slow Convergence: Delays in routing changes propagation.
📏 Administrative Distance
- RIP AD = 120
- OSPF AD = 110
- EIGRP AD = 90
📄 RIP Packet Structure (High-Level)
- Command Field: 1 = Request, 2 = Response
- Route Entries: Contains destination IP, subnet mask, next hop, and metric
🌐 RIP in IPv6 – RIPng
- RIPng: Next generation RIP for IPv6 networks.
- Uses UDP port 521
- Supports: IPv6 prefixes, VLSM, optional authentication
- Configured under interface level in IPv6
⚔️ RIP vs Other Protocols
| Feature | RIP | OSPF | EIGRP |
|---|---|---|---|
| Protocol Type | Distance Vector | Link-State | Hybrid |
| Metric | Hop Count | Cost (Bandwidth) | Bandwidth + Delay |
| Convergence | Slow | Fast | Very Fast |
| Scalability | Poor | Excellent | Good |
| Administrative Distance | 120 | 110 | 90 |
🎯 Example Scenario (Where RIP is Appropriate)
Use Case: A small campus network with fewer than 15 routers.
Scenario: A small office with 3 branches. Each router advertises its networks using RIP v2 with VLSM support.
Result: Simple to set up and manage, but not scalable for large environments.
✅ Conclusion
RIP is best suited for smaller, simple networks. Its limitations — hop count, slow convergence, and bandwidth usage — make it unsuitable for modern, large-scale networks. However, it's useful for understanding fundamental routing concepts and practicing in simulators like Packet Tracer or GNS3.