RIPv1 (Routing Information Protocol version 1) is one of the earliest distance-vector routing protocols used in IP networks. It’s a simple protocol designed for smaller, flat networks. Here’s how RIPv1 works:
Basic Operation #
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Hop Count as Metric: RIPv1 uses hop count as the metric for choosing the best path to a destination network. The maximum allowable hop count is 15, with 16 being considered unreachable.
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Periodic Updates: RIPv1 routers broadcast their entire routing table to all neighboring routers every 30 seconds, regardless of whether there have been changes in the network. These updates are sent to the broadcast address 255.255.255.255.
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Route Learning: When a router receives a routing update, it examines the hop count for each route. If it learns about a new network or a shorter path to an existing network (fewer hops), it updates its routing table with the new route.
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Timers: RIPv1 uses various timers to manage its routing table, including:
- Update Timer: Controls the interval between periodic routing updates (usually 30 seconds).
- Invalid Timer: Determines how long a route must be unreachable before it’s considered invalid (typically 180 seconds).
- Holddown Timer: Prevents regular update messages from reinstating a route that might have become invalid (usually 180 seconds).
- Flush Timer: Time after which a route is removed from the routing table if it’s not reinstated (typically 240 seconds).
Characteristics of RIPv1 #
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Classful Protocol: RIPv1 doesn’t include subnet information in its routing updates. It assumes all networks in the same IP address class use the same subnet mask (classful routing), which makes it unsuitable for modern networks with varying subnet sizes (CIDR and VLSM).
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Broadcasts for Updates: RIPv1 uses broadcasts for its updates, which can lead to increased network load, especially in larger networks.
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Simple Protocol: RIPv1 is easy to configure and manage due to its simplicity. This makes it suitable for small, uncomplicated networks.
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No Authentication: There’s no mechanism for authenticating RIPv1 updates, which can be a security concern.
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Routing Loops: RIPv1 is prone to routing loops and slow to converge in larger networks. Various mechanisms like split horizon, route poisoning, and holddown timers are used to prevent and mitigate routing loops.
Limitations #
- Subnetting: Inability to handle modern subnetting practices is a significant limitation.
- Scalability: Not suitable for larger networks due to its reliance on broadcasting and a flat network structure.
- Inefficient Use of Bandwidth: Periodic broadcast of the entire routing table is bandwidth-intensive.
In summary, RIPv1 is a basic routing protocol best suited for small, homogeneous networks. It’s largely obsolete in modern networking environments due to its limitations in handling subnetting, scalability, and efficiency.
RIPv2 (Routing Information Protocol version 2) is an enhancement over RIPv1, addressing several of its limitations while retaining its basic operation as a simple distance-vector routing protocol. It is more suitable for modern networks compared to RIPv1 due to its support for classless inter-domain routing (CIDR), use of multicast, and route authentication.
Basic Operation of RIPv2 #
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Hop Count as Metric: Like RIPv1, RIPv2 uses hop count as the metric for path selection, with a maximum of 15 hops. Any route with a hop count of 16 is considered unreachable.
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Periodic Updates: RIPv2 also sends updates every 30 seconds, but these updates are multicast to the address 224.0.0.9, reducing unnecessary network load compared to RIPv1’s broadcast updates.
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Route Learning and Timers: RIPv2 operates similarly to RIPv1 in terms of route learning and the use of timers (update, invalid, holddown, and flush timers) to manage the routing information.
Enhancements in RIPv2 #
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Classless Routing (VLSM and CIDR Support): RIPv2 supports classless routing, meaning it includes the subnet mask with each route in updates. This allows for more efficient use of IP addresses and compatibility with variable length subnet masks.
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Multicast Updates: Instead of broadcasting updates to all hosts on a network, RIPv2 multicasts updates to a well-known address, reducing unnecessary traffic on the network.
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Route Authentication: RIPv2 introduces the capability for simple plain text or MD5 authentication of routing updates, enhancing security.
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Route Tagging: It supports route tagging, which is useful for differentiating between routes learned from different sources or for policy-based routing decisions.
Operation Details #
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Sending Updates: When a RIPv2 router sends an update, it includes the IP address, subnet mask, next-hop address, and hop count for each route, enabling more precise routing decisions.
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Receiving Updates: On receiving an update, a router updates its routing table if it learns a new route or a shorter (lower hop count) path to an existing route.
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Preventing Routing Loops: Like RIPv1, RIPv2 uses techniques such as split horizon, route poisoning, and holddown timers to prevent routing loops.
Limitations #
- Scalability: While better than RIPv1, RIPv2 is still limited in scalability and is generally not suitable for very large or complex networks.
- Speed of Convergence: As a distance-vector protocol, RIPv2 has a slower convergence compared to more advanced routing protocols like OSPF or EIGRP.
- Limited Metric: The hop count metric is simplistic and doesn’t consider other important factors like bandwidth or latency.
In summary, RIPv2 retains the simplicity of RIPv1 but adds important features like classless routing, multicast updates, and route authentication. These improvements make it more suitable for somewhat larger and more complex networks than RIPv1, although it’s still generally used in smaller, less complex network environments.