Router

This article is about a computer networking device. For the kind of rotating cutting tool, see wood router. For the type of network router found in many homes, see residential gateway. For the software used in electronic design automation, see routing (EDA).

Cisco 1800 Router

Nortel ERS 8600

Cisco 7600 Enterprise

A router is a computer whose software and hardware are usually tailored to the tasks of routing and forwarding, generally containing a specialized operating system (e.g. Cisco's IOS or Juniper Networks JUNOS and JUNOSe or Extreme Networks XOS), RAM, NVRAM, flash memory, and one or more processors. High-end routers contain many processors and specialized Application-specific integrated circuits (ASIC) and do a great deal of parallel processing. Chassis based systems like the Nortel MERS-8600 or ERS-8600 routing switch, (pictured right) have multiple ASICs on every module and allow for a wide variety of LAN, MAN, METRO, and WAN port technologies or other connections that are customizable. However, with the proper software (such as XORP or Quagga), even commodity PCs can act as routers.

Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.^[1] The term layer 3 switch often is used interchangeably with router, but switch is really a marketing term without a rigorous technical definition. In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types.

Routers operate in two different planes ^[2]:

• Control Plane, in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations,
• Forwarding Plane, which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.