Editing Router (computing) (section)

=== Internet connectivity and internal use ===
Routers intended for ISP and major enterprise connectivity usually exchange routing information using the [[Border Gateway Protocol]] (BGP). {{IETF RFC|4098}} defines the types of BGP routers according to their functions:<ref name="RFC 4098">{{cite IETF |rfc=4098 |author=H. Berkowitz |display-authors=etal |title=Terminology for Benchmarking BGP Device Convergence in the Control Plane |date=June 2005}}</ref>
* ''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 [[IXP]], private peering (or even settlement-free peering) through [[Private Network Interconnect]] (PNI) via the extensive use of [[Exterior Border Gateway Protocol]] (eBGP).<ref>{{Cite web |title=What is the primary role of a router placed at the edge of an ISP network engaging in peering with upstream IP transit providers through eBGP - ITEagers |url=https://iteagers.com/Computer%20Science/Computer%20Networking/21274_What-is-the-primary-role-of-a-router-placed-at-the-edge-of-an-ISP-network-engaging-in-peering-with-upstream-IP-transit-providers-through-eBGP |access-date=2024-02-27 |website=ITEagers |language=en-GB}}</ref>
* 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.<ref name=":0" />
* ''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.<ref name=":0">{{Cite report |url=https://datatracker.ietf.org/doc/rfc4364/ |title=BGP/MPLS IP Virtual Private Networks (VPNs) |last1=Rekhter |first1=Yakov |last2=Rosen |first2=Eric C. |date=February 2006 |publisher=Internet Engineering Task Force |issue=RFC 4364}}</ref>
* ''Customer edge router'' (CE): Located at the edge of the subscriber's network, it interconnects with the PE router for L2VPN services, or direct layer 3 IP hand-off in the case of [[Dedicated line|Dedicated Internet Access]], 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 or [[data center]] organizations.<ref name=":0" />
* [[Core router]]: Resides within an Autonomous System as a backbone to carry traffic between edge routers.<ref>{{cite web |url=http://www.juniper.net/techpubs/qrc/m160-qrc.pdf |title=M160 Internet Backbone Router |publisher=Juniper Networks |access-date=15 January 2011 |url-status=live |archive-url=https://web.archive.org/web/20110920213215/http://www.juniper.net/techpubs/qrc/m160-qrc.pdf |archive-date=20 September 2011}}</ref>
* Within an ISP: In the ISP's autonomous system, a router uses internal BGP to communicate with other ISP edge routers, other [[intranet]] core routers, or the ISP's intranet provider border routers.
* Internet backbone: The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks. See [[default-free zone]] (DFZ). The major ISPs' system routers make up what could be considered to be the current Internet backbone core.<ref>{{cite web|url=http://www.telecomsportal.com/Assets_papers/Routers_&_Netman/Ironbridge_Virt_Bbone_Route.pdf|title=Virtual Backbone Routers|publisher=IronBridge Networks, Inc. September, 2000|access-date=15 January 2011|url-status=live|archive-url=https://web.archive.org/web/20110716203325/http://www.telecomsportal.com/Assets_papers/Routers_%26_Netman/Ironbridge_Virt_Bbone_Route.pdf|archive-date=16 July 2011}}</ref> 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 network]]s based on a combination of BGP and [[Multiprotocol Label Switching]] protocols.<ref>{{cite IETF |title= BGP/MPLS VPNs |rfc-2547 |author1=E. Rosen |author2=Y. Rekhter |date=April 2004}}</ref>
* Port forwarding: In some networks, that rely on legacy IPv4 and NAT, routers (often labeled as NAT boxes) are also used for [[port forwarding]] configuration between RFC1918 address space and their publicly assigned IPv4 address.<ref name="port"/>
* Voice, data, fax, and video processing routers: Commonly referred to as [[access servers]] or [[Gateway (telecommunications)|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 [[Internet Protocol|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.
* Larger networks commonly use [[multilayer switch]]es, with layer-3 devices being used to simply interconnect multiple subnets within the same security zone, and higher-layer switches when [[firewall (computing)|filtering]], [[network address translation|translation]], [[load balancing (computing)|load balancing]], or other higher-level functions are required, especially between zones.