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Encyclopedia :
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ROU :
Routing |
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RoutingThis article describes routing in computer networks, a method of finding paths from origins to destinations, along which information can be passed. See Routing (disambiguation) for other meanings.
Routing is a core concept of the Internet and many other networks. Routing provides the means of discovering paths along which information (usually, but not always, packets) can be sent. Circuit-based networks, such as the voice telephone network, also perform routing, to find paths for calls through the network fabric. Automatic routing makes networks autonomous. Such networks can use their routing to find the best route to deliver data to a destination; choices are made depending upon goals such as finding the shortest distances and the fastest links available through a choice of network connections. This allows the network to route around network failures and blockages, and can make many aspects of the day to day running of such networks automatic, and free from the need for human intervention. The actual process of passing logically addressed packets from their local subnetwork toward their ultimate destination is called forwarding. It is closely related to routing, in that routing tells the forwarding where to send packets, but they are logically completely separate. In large networks, packets may pass through many intermediary destinations before reaching their destination. Routing and forwarding both occur at layer 3 of the OSI seven-layer model. Hubs and switches move data on what appears (to the connected computers) to be the local network, and are invisible to connected computers, while the router is explicitly visible to them. See the router article for a description of the hardware technology and manufacturers of routers. The rest of this article describes routing in a hardware-independent way. Knowing where to send packets requires a knowledge of the structure of the network. In small networks, routing can be very simple, and is often configured by hand. In large networks the topology of the network can become complex, and may change constantly, making the problem of constructing the routing tables very complex. As routers can only recalculate the best routes very slowly relative to the rate of arrival of packets, routers keep a routing table that maintains a record of only the best possible routes to certain network destinations and the routing metrics associated with those routes. Routed versus routing protocolThere is often confusion between routed protocol and routing protocol:
Routing algorithms use two basic technologies:
A routing metric consists of any value used by routing algorithms to determine whether one route is superior to another. Metrics can cover such information as bandwidth, delay, hop count, path cost, load, MTU, reliability, and communication cost. The routing table stores only the best possible routes, while link-state or topological databases may store all other information. Administrative distance is the feature used by routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each routing protocol is prioritized in order of most to least reliable using an administrative distance value. Depending on the relationship of the router relative to other autonomous systemss, various classes of routing protocols exist:
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This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License. |
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| © 2008 Chamas Enterprises Inc. |
