Router (computing)

Router (computing)
Name	Router
Caption	A modern enterprise router, the Cisco ASR 1002-X.
Inventor	Wesley Clark (concept), Leonard Kleinrock (theory)
First produced	1980s
Related	Gateway, Switch, Modem

Router (computing). A router is a networking device that forwards data packets between computer networks, performing the critical function of traffic directing on the Internet and within private networks. Routers operate at the network layer (Layer 3) of the OSI model, using information contained in packet headers and a routing table to determine the best path for forwarding. They connect disparate networks, such as linking a home LAN to an ISP, and are fundamental to the operation of global internetworks.

Function

The primary function of a router is to connect multiple networks and route packets between them based on their destination IP address. It examines the header of each incoming packet, consults its internal routing table, and decides the optimal outgoing interface to send the packet toward its final destination, a process known as packet switching. Routers also perform NAT, allowing multiple devices on a private network to share a single public IP address, and often incorporate firewall capabilities to filter traffic. By exchanging routing information with other routers using protocols like BGP and OSPF, they dynamically build maps of the network to avoid congested or failed paths.

Types

Routers are categorized by their deployment scale and purpose. Core routers reside in the backbone of the Internet, operated by major ISPs and Tier 1 networks like AT&T and Deutsche Telekom. Edge routers, or access routers, connect an organization's network to external networks, while wireless routers integrate a Wi-Fi access point for home and small office use. Virtual routers are software implementations running on general-purpose servers, often in cloud environments like AWS or Microsoft Azure. Specialized routers include CPE provided by ISPs and industrial routers designed for harsh environments.

Hardware components

A router's hardware architecture is optimized for high-speed packet processing. Central to its design is the CPU or specialized ASICs that execute routing algorithms. It contains RAM for storing routing tables and ARP caches, and non-volatile memory like Flash memory for holding the operating system. Physical network interfaces, such as Ethernet ports, SFP+ slots, or DSL modems, provide connectivity. Critical supporting components include a power supply unit, cooling fans, and in larger models, redundant power supplies and modular line cards for expansion, as seen in chassis-based systems from Juniper Networks.

Software and firmware

The router's operating system, often called firmware or IOS (as in Cisco's proprietary system), controls all hardware functions. This software implements routing protocols (RIP, EIGRP), manages the forwarding information base, and provides a management interface via CLI or web interface. Open-source router operating systems, such as OpenWrt and DD-WRT, are popular for modifying consumer-grade hardware. The software is responsible for critical services like DHCP, QoS traffic shaping, and VPN termination (e.g., IPsec, OpenVPN).

Routing algorithms

Routing algorithms determine the best path for data through a network. Static routing involves manually configured paths, while dynamic routing uses protocols to automatically share route information. Distance-vector algorithms, like the RIP, determine direction and distance. Link-state algorithms, such as OSPF and IS-IS, build a complete map of the network topology for more efficient routing. For inter-domain routing across the Internet, the de facto standard is the path-vector protocol BGP, which is central to the policies of Autonomous Systems.

Security considerations

Routers are high-value targets for attacks, as compromising one can redirect or intercept vast amounts of traffic. Common threats include unauthorized access via default credentials, exploitation of vulnerabilities in services like UPnP, and DDoS attacks aimed at exhausting resources. Mitigation involves disabling unused services, implementing strong access control lists (ACL), keeping firmware updated, and using encrypted management protocols like SSH. FBI advisories often warn about botnets like Mirai that exploit routers. Advanced security features include IDS/IPS and deep packet inspection.

Historical development

The conceptual foundation for packet switching and routing was laid in the 1960s by Leonard Kleinrock and others working on the ARPANET. The first true router, then called an IMP, was developed by BBN Technologies under contract from the DARPA. In the 1980s, William Yeager at Stanford University and later engineers at Cisco Systems, founded by Leonard Bosack and Sandy Lerner, commercialized multiprotocol routers, enabling the interconnection of disparate network technologies. The exponential growth of the Internet in the 1990s, driven by WWW standards from CERN and Tim Berners-Lee, cemented the router's role as the indispensable backbone device. Category:Computer networking Category:Networking hardware Category:Internet architecture