Distance Vector Routing is a class of routing protocols used in computer networks to determine the best path for data packets based on distance or “hop count.” These routing protocols are simple and work by periodically exchanging routing information with neighboring routers to build and maintain routing tables. Here are the key characteristics and principles of distance vector routing:
- Hop Count Metric: Distance vector routing protocols use the number of “hops” or network segments as a metric to determine the distance between routers and network destinations. The metric represents the number of routers a packet must pass through to reach its destination.
- Periodic Updates: Routers using distance vector routing periodically broadcast their routing tables to neighboring routers. These updates inform neighboring routers of the routes the sender is aware of and the corresponding hop counts.
- Full Routing Tables: Each router maintains a complete routing table that lists all known network destinations and their corresponding hop counts. These tables are sent in updates to neighboring routers.
- RIP (Routing Information Protocol): RIP is a well-known example of a distance vector routing protocol. It uses a hop count metric and updates routing tables every 30 seconds. RIP has a maximum hop count limit (15 hops) to prevent routing loops.
- Split Horizon: Distance vector routing protocols often employ a technique called “split horizon” to prevent routing loops. With split horizon, a router does not advertise routes back to the router from which it learned those routes.
- Route Poisoning: To quickly inform other routers about the unavailability of a route, distance vector protocols use a technique called “route poisoning.” When a router determines that a route is unreachable, it advertises the route with an infinite metric (e.g., 16 hops) to indicate unreachability.
- Count to Infinity: A limitation of distance vector routing is the “count to infinity” problem. If a router goes down or a link fails, it may take some time for routers to converge and update their routing tables, potentially leading to routing loops or inaccurate routing information.
- Convergence Time: Convergence time, or the time it takes for all routers in a network to reach a consistent view of the network topology, can be relatively slow in distance vector routing protocols, especially in large networks.
- Limited Scalability: Distance vector routing is generally less scalable and efficient than link-state routing protocols (e.g., OSPF) because it requires routers to maintain and exchange complete routing tables.
While distance vector routing protocols are simple and easy to configure, they are less suitable for large and complex networks due to scalability and convergence time issues. More advanced routing protocols, such as link-state protocols or hybrid routing protocols, are often preferred in modern network environments. Distance vector routing is still found in some smaller networks or legacy setups.
