D-Link DFL-2500 User Guide - Page 91
Dynamic Routing
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72 Chapter 10. Routing simply drop the packet. Therefore, static routing is often used to make the minimal set of routes to reach directly connected networks only. 10.3.2 Dynamic Routing Complementing to static routing algorithm, Dynamic Routing adapts to changes of network topology or traffic loads automatically. It learns all the directly connected networks first, and gets further routes information from other routers that are running the same algorithm. The algorithm then sorts the routes it collected, selects the most suitable route for a destination it has learned, appends the route into its routing table, and distributes this information to other routers. Dynamic routing responses to routing updates on the fly and is more susceptible to problems such as routing loops. In the Internet, two types of dynamic routing algorithm are typically used: a Distance Vector(DV) algorithm & a Link State(LS) algorithm. How it decides the "best" route and shares the update information with other routers depends on the type of the algorithm applied. Distance vector algorithm Distance vector (DV) algorithm is a decentralized routing algorithm, computing the "best" path in a distributed manner. Each router computes the costs of its own attached links, and shares the route information only with its neighbor routers. The router gradually learns the least-cost path by iterative computation and knowledge exchange with its neighbors. The Routing Information Protocol(RIP) is a well-known DV algorithm. RIP sends update message regularly, and reflects the routing changes in the routing table. Its path determination is based on the length of the path - the number of intermediate routers, or the so-called hops. After updating its own routing table, the router immediately begins transmitting its entire routing table to its neighbor routers to inform the change. Link state algorithm Different from the DV algorithms, Link state (LS) algorithm enables the routers to keep routing tables that reflect the topology of the entire network, a global view of the routing information. As defined in this algorithm, each router broadcasts its attached links and link costs to all the other routers in the network. A router, upon receiving broadcasts from the D-Link Firewalls User's Guide