A router is a device that directs (routes) data from one path to another in a network. Routers base their switching information on one or more information parameters contained within the packet of data they receive. These parameters may include the destination address, availability of a transmission path or communications channel, maximum allowable amount of transmission delay a packet can accept, along with other key parameters. Routers that connect data paths between different types of networks are sometimes called gateways.

Routers provide some of the same functionality as network switches. Their primary function is to provide a path for each routable packet to its destination. When a router is initially installed into a network, it begins its life by requesting a data network address. Using this data network address, it sends (broadcasts) messages to nearby routers and begins to store address connections of routers that are located around it. Routers regularly exchange their connection information (lists of devices it is connected to) with nearby routers to help them keep the latest packet routing information.

A router can make decisions on where to forward packets dependent on a variety of factors including the maximum transmission distance or packet priority. Distance vector routing and link state routing allow the router to select paths that match the needs of the data that is being sent through it.

Some routers may use fixed (static) routing tables that are manually programmed by the network administrator instead of dynamically created routing tables. The use of static routing tables may seem to be inflexible, however the use of static routing ensures other router’s that may have corrupt routing tables are not able to change or influence the routing table.