Router

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A router interconnects two or more computer networks, and selectively interchanges packets of data between them. Each data packet contains address information that a router can use to determine if the source and destination are on the same network, or if the data packet must be transferred from one network to another. When multiple routers are used in a large collection of interconnected networks, the routers exchange information about target system addresses, so that each router can build up a table showing the preferred paths between any two systems on the interconnected networks.

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When multiple routers are used in a large collection of interconnected networks, the routers exchange information, so that each router can build up a reference table showing the preferred paths between any two systems on the interconnected networks.

A router can have many interface connections, for different physical types of network (such as copper cables, fiber optic, or wireless transmission). It may contain firmware for different networking protocol standards. Each network interface device is specialized to convert computer signals from one protocol standard to another.

Routers can be used to connect two or more logical subnets, each having a different network address. The subnets addresses in the router do not necessarily map directly to the physical interfaces of the router.[1] The term "layer 3 switching" is often used interchangeably with the term "routing". The term switching is generally used to refer to data forwarding between two network devices with the same network address. This is also called layer 2 switching or LAN switching.

Conceptually, a router operates in two operational planes (or sub-systems):[2]

  • Control plane: where a router builds an address table (called routing table) that records where a packet should be forwarded, and through which physical interface.It does this by using either statically configured statements (called static routes), or alternatively, by exchanging information with other routers in the network through a dynamical routing protocol.
  • Forwarding plane: The router actually forwards traffic, (called data packets in Internet Protocol language) from incoming interfaces to outgoing interfaces destination addresses that the packet header contains. It performs this function by following rules derived from the routing table that has been recorded in the control plane.

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