RIP (Routing Information Protocol)
One of the oldest Distance Vector protocols. While rarely used in modern enterprise cores, it is still simple, useful for small edge networks, and a staple of exam curriculums.
1. RIPv1 vs RIPv2
RIPv1 is legacy and should never be used. RIPv2 added essential features for modern networking.
| Feature | RIPv1 | RIPv2 |
|---|---|---|
| Addressing | Classful (No Subnet Mask sent) | Classless (Sends VLSM) |
| Updates | Broadcast (255.255.255.255) | Multicast (224.0.0.9) |
| Authentication | No | Yes (MD5 / Plaintext) |
| Manual Summary | No | Yes |
2. Limitations
- Hop Count Limit: The maximum metric is 15. A hop count of 16 is considered "Infinite" (Unreachable). This limits the network diameter.
- Slow Convergence: Relies on periodic updates (every 30s). It can take minutes to detect a failure and converge.
- No Neighbor Relationships: RIP routers do not form formal adjacencies (like OSPF/EIGRP). They just blast updates out the interface.
3. Timers & Loop Prevention
Because RIP is "Distance Vector" (Rumor based), it is prone to loops. It uses several mechanisms to prevent them:
- Split Horizon: Never send a route back out the same interface I learned it from.
- Poison Reverse: Send the route back, but with a metric of 16 (Poisoned), to explicitly confirm it's unreachable.
- Triggered Updates: Send an update immediately when a change occurs, rather than waiting for the timer.
Standard Timers
| Timer | Default | Function |
|---|---|---|
| Update | 30s | How often routing table is sent. |
| Invalid | 180s | If no update received, mark route as invalid (Holddown). |
| Flush | 240s | Time to actually remove the route from the table. |
References
- RFC 2453: RIP Version 2 - Defines multicast updates and authentication.
- RFC 1058: Routing Information Protocol - The original specification (Legacy).