Routing Information Protocol (RIP)

Routing Information Protocol (RIP) is a dynamic routing protocol responsible for routing tasks in IP-based networks. Standardized by RFC 1058 in 1988, RIP is one of the earliest routing protocols based on the distance-vector algorithm. It uses "hop count" as a metric to determine the shortest path between routers. The core logic of the protocol is to prefer the path that contains the fewest number of routers (hops) to reach a destination network.

In its operational principle, each router periodically sends its routing table to neighboring routers. This table includes all known destination networks and the number of hops required to reach them. Each router receives this information and updates its own routing table accordingly.

RIP Versions

There are three main versions of the RIP protocol developed over time to meet evolving needs:

• RIPv1: The initial version. It supports only classful routing. It does not send subnet mask information in updates. It operates using the broadcast address 255.255.255.255 and lacks authentication support.
• RIPv2: An enhanced version. It supports classless routing and includes subnet mask information. It uses multicast (224.0.0.9) and supports authentication.
• RIPng: The IPv6-compatible version. It is the adaptation of RIP for IPv6 and is defined in RFC 2080.

Operational Principle

RIP sends routing information via all active interfaces every 30 seconds. Updates are transmitted over UDP port 520. Each router evaluates the received information and updates its routing table accordingly. If there are multiple entries for the same route, RIP selects the one with the lowest hop count.

The hop count is incremented by 1 as it is forwarded. When the hop count reaches 16, the destination is considered unreachable. Therefore, RIP supports a maximum of 15 hops and is not suitable for larger networks.

Timers

RIP uses three different timers to manage routing information:

• Update Timer (30 seconds): Sends the full routing table to neighbors.
• Invalid Timer (90 seconds): The time before a route is considered invalid.
• Flush Timer (240 seconds): The time after which an invalid route is removed from the table.

Loop Prevention Techniques

RIP uses several techniques to prevent routing loops:

• Split Horizon: A route learned on an interface is not advertised back through the same interface.
• Route Poisoning: An invalid route is advertised with a hop count of 16 to remove it from the network.
• Holddown Timer: Prevents acceptance of potentially incorrect routes for a certain period.
• Triggered Updates: Sends an immediate update when a routing table change occurs.

Limitations and Use Cases

Due to its simplicity, RIP is suitable for small and medium-sized networks. However, the 15-hop limitation makes it inadequate for larger and more complex networks. Additionally, the convergence time is longer compared to modern protocols. For these reasons, more advanced protocols such as OSPF or EIGRP are preferred today.

Configuration and Implementation Example

RIP configuration is typically carried out using three basic commands:

These commands are used to select the RIP version and specify the networks to be advertised. On each router, directly connected networks must be advertised individually.