Router (computing)
Device that directs data packets across computer networks.
A router is a computer and networking device that forwards data packets between computer networks, including internetworks such as the global Internet. Routers perform the traffic directing functions on the Internet, reading network addresses in packet headers and using routing tables or policies to direct packets to their next destination. They are essential for connecting home networks, enterprises, and internet service providers, and range from small office/home office models to powerful core routers that handle high-speed data along the Internet backbone.
The fundamental concept of a router originated in the 1960s, with Donald Davies proposing a switching node using software for the NPL network, and Wesley Clark independently conceiving a similar idea for the ARPANET, which became the Interface Message Processor (IMP). The first such devices were built with Honeywell 516 computers and delivered to UCLA and other research sites in 1969. The modern router, initially called a gateway, emerged from the International Network Working Group, which designed devices that could connect dissimilar networks and operated without guaranteeing reliable delivery—a principle known as the end-to-end principle. Early implementations included the CYCLADES network in France, the PARC Universal Packet system at Xerox, and a DARPA program that led to the TCP/IP architecture. The first true IP router was developed at BBN during 1975–1976, using PDP-11 computers, and by the end of 1976 three such routers were operational in the experimental Internet. Multiprotocol routers, capable of handling protocols beyond TCP/IP, were independently created at MIT and Stanford in 1981. Modern routers range from home devices that forward packets between local computers and the Internet to enterprise and core routers that use application-specific integrated circuits (ASICs) for high-speed forwarding and advanced filtering. While routers can be built from standard computer parts, most are specialized embedded systems, and many modern operating systems like Junos and NX-OS are derived from Unix.
- field
- Computer networking
- known_for
- Forwarding data packets between networks, enabling internetworking
Lore & Background
Modern routers are specialized computers, often built as embedded systems, though some can be assembled from standard computer components. They vary widely in appearance, from small, plastic home-office boxes with a few ports to large, rack-mounted enterprise units with numerous interfaces and indicator lights. Their range extends from these home and small office devices, which forward IP packets between local computers and the internet, to enterprise routers connecting large business or ISP networks, and finally to powerful core routers that move data at high speed along the optical fiber lines of the internet backbone. Defining characteristics include the ability to connect two or more data lines from different IP networks, read the network address in a packet header to determine the ultimate destination, and use a routing table or policy to direct the packet to the next network. Modern high-speed routers employ network processors or specialized hardware acceleration for functions like packet forwarding and IPsec encryption, moving beyond the early software-based forwarding on a CPU. They are multiprotocol devices, handling both IPv4 and IPv6, and are simpler than earlier routers that processed protocols like AppleTalk or IPX. Their operation involves two simultaneous processing units: a control plane that maintains the routing table, and a data plane that forwards packets.
Reader's Guide
Routers are foundational to modern internetworking, enabling the global Internet by directing data packets between diverse networks. Their development from early software-based forwarding on CPUs to application-specific integrated circuits (ASICs) has dramatically increased performance and added advanced filtering and firewall capabilities. The hierarchical internetworking model divides enterprise networks into access, distribution, and core layers, with routers optimized for each role—from low-cost SOHO models to powerful core routers interconnecting ISPs. The control plane maintains routing tables and builds a forwarding information base, while the forwarding plane handles packet forwarding. Routers have evolved from general-purpose minicomputers to specialized embedded systems, with operating systems like Cisco IOS, Junos, and NX-OS. Their significance lies in enabling connectivity within enterprises, between enterprises and the Internet, and among ISPs, supporting both wired and wireless transmission. The end-to-end principle, which leaves reliable delivery to hosts, remains a key design concept.
Did You Know?
- Early routers used software-based forwarding on a CPU; more sophisticated devices now use application-specific integrated circuits (ASICs).
Frequently Asked Questions
What is a router in computing?
A router is a networking device that forwards data packets between separate computer networks by inspecting the address in each packet's header and consulting a routing table to pick the next hop. It is the core mechanism that makes internetworking possible, from a home Wi-Fi box to the global Internet.
How does a router decide where to send a given packet?
It reads the destination network address stored in the packet header and matches it against a routing table or a set of policy rules to determine the next network to forward the packet to. This lookup-and-forward cycle repeats at each hop until the packet reaches its final destination.
Why are routers considered essential to modern networking?
Without routers, isolated networks could not exchange data, so the interconnected Internet simply would not exist. They cover an enormous range of scale, from small office/home-office units to high-speed core routers that carry backbone traffic across continents.
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