router

A router is a device that forwards data packets between computer networks, using destination IP addresses to determine the next hop. It connects networks such as a home local area network to an Internet service provider, or links multiple internal networks within an organization. It operates at Layer 3 of the OSI model.

Key functions include packet forwarding, routing decisions based on routing tables, and the use of routing protocols to exchange information about network reachability. Routers often provide services such as Network Address Translation (NAT), firewall filtering, DHCP server functionality, DNS relay, and support for virtual private networks (VPNs). They use static routes or dynamic routing protocols like RIP, OSPF, EIGRP, and BGP to build routes.

Types include home or small office/home office (SOHO) routers that combine a switch, wireless access point, and router; enterprise edge routers that connect to Internet service providers and large networks; and core routers that handle high-speed internal backbones. Many routers include wired Ethernet interfaces and wireless radios, and support quality of service (QoS) and multiple WAN links.

In operation, a router examines the destination address of each incoming packet, consults its routing table, and forwards the packet toward its next hop. Routing tables are populated manually (static routing) or automatically through dynamic routing protocols. Security features, such as NAT and firewalls, help control traffic between networks and protect internal resources.

History and context: Early Internet relied on gateways performing routing decisions; the term router reflects its function of determining routes. Modern routers support advanced features and play a central role in Internet connectivity, network segmentation, and traffic management.