Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops in RIP is 15, which means that any network that is 16 hops away or more is considered unreachable.
Versions of RIP:
RIPv1:
- Classful routing protocol.
- Does not support CIDR (Classless Inter-Domain Routing) or VLSM (Variable Length Subnet Mask).
- Updates are broadcasted.
- No authentication feature.
RIPv2:
- Classless routing protocol.
- Supports CIDR and VLSM.
- Uses multicast to send updates to 224.0.0.9.
- Supports simple password authentication.
RIP Features and Characteristics:
- Routing Updates: RIP routers transmit their entire routing table to their immediate neighbors every 30 seconds.
- Metric: The only metric used by RIP is hop count. A hop count of 16 is considered an infinite distance (i.e., the network is unreachable).
- Timers: RIP uses various timers to regulate its performance:
- Update Timer: 30 seconds (time interval for regular routing updates).
- Invalid Timer: 180 seconds (time after which a route is considered invalid if no update is received).
- Hold Down Timer: 180 seconds (time during which routing information is suppressed or held down).
- Flush Timer: 240 seconds (time after which a route is removed from the routing table).
- Split Horizon: This is a technique to prevent loops in RIP by ensuring that route information is not sent back in the direction from which it was received.
- Route Poisoning: When a route becomes invalid, RIP advertises it with a metric of 16 to inform other routers about the unreachable route.
- Triggered Updates: When a router detects a network topology change, it sends an update immediately rather than waiting for the next regular update.
Limitations of RIP:
- Scale: Due to the maximum hop count of 15, RIP is not suitable for large networks.
- Convergence: RIP can be slow to converge (adapt to network changes), especially in larger networks. This can lead to routing loops during the period of convergence.
- Traffic: RIP’s periodic full-table updates can be inefficient, especially on networks with low bandwidth links.
Despite its limitations, RIP’s simplicity made it popular in the early days of networking. However, in modern networks, RIP is largely obsolete, replaced by more advanced protocols like OSPF and EIGRP.