IP routing

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IP routing is the application of traffic routing methodologies to IP networks. This involves technologies, protocols, structure, administrations, and policies of the worldwide Internet infrastructure. In each IP network node, IP routing involves the determination of a suitable path for a network packet from a source to its destination. The process uses rules, obtained from either static configuration or dynamically with routing protocols, to select specific packet forwarding methods to direct traffic to the next available intermediate network node one hop closer to the desired final destination. The total path potentially spans multiple computer networks.

Networks are separated from each other by specialized hosts, called gateways or routers with specialized software support optimized for routing. IP forwarding algorithms in most routing software determine a route through a shortest path algorithm. In routers, packets arriving at an interface are examined for source and destination addressing and queued to the appropriate outgoing interface according to their destination address and a set of rules and performance metrics. Rules are encoded in a routing table that contains entries for all interfaces and their connected networks. If no rule satisfies the requirements for a network packet, it is forwarded to a default route. Routing tables are maintained either manually by a network administrator, or updated dynamically by a routing protocol.

A routing protocol specifies how routers communicate and share information about the topology of the network, and the capabilities of each routing node. Different protocols are often used for different topologies or different application areas. For example, the Open Shortest Path First (OSPF) protocol is generally used within an enterprise and the Border Gateway Protocol (BGP) is used on a global scale.^[1] BGP is the de facto standard for worldwide Internet routing.