Katana VentraIP

Router (computing)

A router[a] is a computer and networking device that forwards data packets between computer networks, including internetworks such as the global Internet.[2][3][4]

This article is about the network device. For the woodworking tool, see Router (woodworking).

A router is connected to two or more data lines from different IP networks. When a data packet comes in on a line, the router reads the network address information in the packet header to determine the ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Data packets are forwarded from one router to another through an internetwork until it reaches its destination node.[5]


The most familiar type of IP routers are home and small office routers that forward IP packets between the home computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks to powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone.


Routers can be built from standard computer parts but are mostly specialized purpose-built computers. Early routers used software-based forwarding, running on a CPU. More sophisticated devices use application-specific integrated circuits (ASICs) to increase performance or add advanced filtering and firewall functionality.

: A router maintains a routing table that lists which route should be used to forward a data packet, and through which physical interface connection. It does this using internal pre-configured directives, called static routes, or by learning routes dynamically using a routing protocol. Static and dynamic routes are stored in the routing table. The control-plane logic then strips non-essential directives from the table and builds a forwarding information base (FIB) to be used by the forwarding plane.

Control plane

: This unit forwards the data packets between incoming and outgoing interface connections. It reads the header of each packet as it comes in, matches the destination to entries in the FIB supplied by the control plane, and directs the packet to the outgoing network specified in the FIB.

Forwarding plane

When multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a routing protocol. Each router builds up a routing table, a list of routes, between two computer systems on the interconnected networks.[6][7]


The software that runs the router is composed of two functional processing units that operate simultaneously, called planes:[8]

Edge router or inter-AS border router: Placed at the edge of an ISP network, where the router is used to peer with the upstream IP transit providers, bilateral peers through , private peering (or even settlement-free peering) through Private Network Interconnect (PNI) via the extensive use of Exterior Border Gateway Protocol (eBGP).[26]

IXP

Provider Router (P): A Provider router is also called a transit-router, it sits in an MPLS network and is responsible for establishing label switched paths between the PE routers.

[27]

Provider edge router (PE): An MPLS-specific router in the network's access layer that interconnects with customer edge routers to provide layer 2 or layer 3 VPN services.

[27]

Customer edge router (CE): Located at the edge of the subscriber's network, it interconnectswith the PE router for L2VPN services, or direct layer 3 IP hand-off in the case of , if IP Transit services are provided through an MPLS core, the CE peers with the PE using eBGP with the public ASNs of each respective network. In the case of L3VPN services the CE can exchange routes with the PE using eBGP. It is commonly used in both service provider and enterprise/Data centre organizations.[27]

Dedicated Internet Access

: Resides within an Autonomous System as a backbone to carry traffic between edge routers.[28]

Core router

Within an ISP: In the ISP's autonomous system, a router uses internal BGP to communicate with other ISP edge routers, other core routers, or the ISP's intranet provider border routers.

intranet

Internet backbone: The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks. See (DFZ). The major ISPs' system routers make up what could be considered to be the current Internet backbone core.[29] ISPs operate all four types of the BGP routers described here. An ISP core router is used to interconnect its edge and border routers. Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multiprotocol Label Switching protocols.[30]

default-free zone

Port forwarding: In some networks, that rely on legacy IPv4 and NAT, routers (often labelled as NAT boxes) are also used for configuration between RFC1918 address space and their publicly assigned IPv4 address.[11]

port forwarding

Voice, data, fax, and video processing routers: Commonly referred to as or gateways, these devices are used to route and process voice, data, video and fax traffic on the Internet. Since 2005, most long-distance phone calls have been processed as IP traffic (VOIP) through a voice gateway. Use of access server-type routers expanded with the advent of the Internet, first with dial-up access and another resurgence with voice phone service.

access servers

Larger networks commonly use , with layer-3 devices being used to simply interconnect multiple subnets within the same security zone, and higher-layer switches when filtering, translation, load balancing, or other higher-level functions are required, especially between zones.

multilayer switches

Mobile broadband modem

Modem

Residential gateway

Switch virtual interface

Wireless router