parts and functions of a router

control plane

A router maintains a routing table that lists which route should be used to forward a data packet, and through which physical interface connection.

router

A router[a] is a networking device that forwards data packets between computer networks.

core router

A core router resides within an Autonomous System as a back bone to carry traffic between edge routers.

access routers

Access routers, including 'small office/home office' (SOHO) models, are located at customer sites such as branch offices that do not need hierarchical routing of their own.

edge router

Also called a provider edge router, is placed at the edge of an ISP network.

distribution routers

Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location.

security

External networks must be carefully considered as part of the overall security strategy. A router may include a firewall, VPN handling, and other security functions, or these may be handled by separate devices.

core

In enterprises, a core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations.

internal connectivity

In the ISP's Autonomous System, a router uses internal BGP to communicate with other ISP edge routers, other intranet core routers.

internal use

Larger networks commonly use multilayer switches, with layer 3 devices being used to simply interconnect multiple subnets within the same security zone.

internet backbone

The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks.

forwarding plane

The router forwards data packets between incoming and outgoing interface connections. It routes them to the correct network type using information that the packet header contains.