Routing: Difference between revisions

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''This article discusses ''routing'' in computer networks. For other meanings, see [[routing (disambiguation)]].''

'''Routing''' is thea means of discovering paths in [[networks]]; typically [[communicationcomputer networks]], to provide paths through the [[Network topology|network fabric]] along which information can be sent. In [[computer networks]], the data is split up into [[packet]]s, each handled individually. [[Telecommunication circuit|Circuit]]-based networks, such as the [[PSTN|voice telephone network]], also perform routing, to find paths for [[telephone call]]s.

Routing directs [[forwarding]], the passing of logically addressed packets from their source toward their ultimate destination through intermediary [[nodes]], called [[routers]]. Forwarding is usually directed by ''routing tables'' within the routers, which maintain a record of the best routes to various network destination locations; thus, the construction of routing tables is the primary goal of routing.

Small networks may involve hand configuration of routing tables. Large networks involve complex topologies and may change constantly, making the constructing of routing tables very problematic. Nevertheless, most of the [[PSTN]] uses pre-computed routing tables, with fallback routes if the most direct route is blocked:; see [[routing in the PSTN]]. Automatic''Dynamic [[routing'' protocol]]s attemptattempts to solve this problem withby dynamically updatedconstructing routing tables. These are updated intermittently by the routing softwareautomatically, based on information carried by the [[routing protocol]]s, and allow the network to be nearly autonomous in avoiding network failures and blockages.

Routing is usually directed by ''routing tables'', which maintain a record of the best routes to various network destinaion locations.

Dynamic routing dominates the Internet. However, the configuration of the routing protocols often requires a skilled touch; it should not be supposed that networking technology has developed to the point where routing is a completely automatic operation.

In [[packet switched]] networks, such as the [[Internet]], the data is split up into [[packet]]s, each labeled with the complete destination address and routed individually. [[Circuit switched]] networks, such as the [[PSTN|voice telephone network]], also perform routing, to find paths for [[circuit]]s, such as [[telephone call]]s, over which large amounts of data can be sent.

Small networks may involve hand configuration. Large networks involve complex topologies and may change constantly, making the constructing of routing tables very problematic. Nevertheless, most of the [[PSTN]] uses pre-computed routing tables, with fallback routes if the most direct route is blocked: see [[routing in the PSTN]]. Automatic [[routing protocol]]s attempt to solve this problem with dynamically updated routing tables. These are updated intermittently by the routing software, based on information carried by the routing protocol, and allow the network to be nearly autonomous in avoiding network failures and blockages.

Routing directs [[forwarding]], the passing of logically addressed packets from their local [[subnetwork]] toward their ultimate destination. 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]].

The hardware used in routing includes [[Ethernet hub|hub]]s, [[network switch|switches]] and [[router]]s.