Editing Router (computing) (section)

== Applications ==
[[File:Adsl connections.jpg|thumb|right|A home or small office [[DSL router]] showing the [[telephone socket]] ''(left, white)'' to connect it to the internet using [[ADSL]], and [[Ethernet]] jacks ''(right, yellow)'' to connect it to home computers and printers]][[File:Sprouter100g.jpg|thumb|A carrier class router with [[10 Gigabit Ethernet|10G]]/[[100 Gigabit Ethernet|40G]]/[[100G]] interfaces and redundant processor/power/fan modules]]

A router may have interfaces for multiple types of [[physical layer]] connections, such as copper cables, [[fiber optic]], or [[wireless]] transmission. It can also support multiple [[network layer]] transmission standards. Each network interface is used to enable data packets to be forwarded from one transmission system to another. Routers may also be used to connect two or more logical groups of computer devices known as [[subnets]], each with a unique [[network prefix]].

Routers may provide connectivity within enterprises, between enterprises and the Internet, or between [[internet service provider]]s' (ISPs') networks, they are also responsible for directing data between different networks.<ref>{{Cite web |title=Which networking component is responsible for directing data between different networks - ITEagers |url=https://iteagers.com/Computer%20Science/Computer%20Networking/446_Which-networking-component-is-responsible-for-directing-data-between-different-networks |access-date=2024-02-27 |website=ITEagers |language=en-GB}}</ref> The largest routers (such as the [[Cisco CRS-1]] or [[Juniper Networks|Juniper]] PTX) interconnect the various ISPs, or may be used in large enterprise networks.<ref>{{cite web|url=http://my-technet.com/index.php/cisco/setting-up-netflow-on-cisco-routers/|title=Setting uo Netflow on Cisco Routers|publisher=MY-Technet.com date unknown|access-date=15 January 2011|url-status=live|archive-url=https://web.archive.org/web/20110714141500/http://my-technet.com/index.php/cisco/setting-up-netflow-on-cisco-routers/|archive-date=14 July 2011}}</ref> Smaller routers usually provide connectivity for typical home and office networks.

All sizes of routers may be found inside enterprises.<ref name="port">{{cite web|url=http://social.technet.microsoft.com/wiki/contents/articles/windows-home-server-router-setup.aspx|title=Windows Home Server: Router Setup|publisher=Microsoft Technet 14 Aug 2010|access-date=15 January 2011|url-status=live|archive-url=https://web.archive.org/web/20101222175405/http://social.technet.microsoft.com/wiki/contents/articles/windows-home-server-router-setup.aspx|archive-date=22 December 2010}}</ref> The most powerful routers are usually found in ISPs, academic and research facilities. Large businesses may also need more powerful routers to cope with ever-increasing demands of [[intranet]] data traffic. A [[hierarchical internetworking model]] for interconnecting routers in large networks is in common use.<ref>{{cite book
  | last = Oppenheimer
  | first = Pr
  | title = Top-Down Network Design
  | publisher = Cisco Press
  | year = 2004
  | location = Indianapolis
  | isbn = 978-1-58705-152-4}}</ref> Some routers can connect to [[Data service unit]]s for [[Digital Signal 1|T1 connections]]<ref>{{cite book | url=https://books.google.com/books?id=SQ2WAAAAQBAJ&dq=data+service+unit+t1&pg=PT89 | title=A Practical Guide to Advanced Networking | isbn=978-0-13-335400-3 | last1=Beasley | first1=Jeffrey S. | last2=Nilkaew | first2=Piyasat | date=5 November 2012 | publisher=Pearson Education }}</ref><ref>{{cite book | url=https://books.google.com/books?id=tGi5xrjPsKoC&dq=data+service+unit+t1&pg=PA43 | title=Configuring Cisco AVVID | isbn=978-0-08-047673-5 | last1=Lawson | first1=Wayne | date=8 February 2001 | publisher=Elsevier }}</ref><ref>{{cite web | url=https://books.google.com/books?id=aDzmTlX49OQC&dq=data+service+unit+t1&pg=PA63 | title=Computerworld | date=23 January 1995 }}</ref> via serial ports.<ref>{{cite web | url=https://www.cisco.com/c/en/us/td/docs/routers/access/interfaces/ic/hardware/installation/guide/ser_hwic.html | title=Serial Interface Cards }}</ref><ref>{{cite web | url=https://www.cisco.com/c/en/us/td/docs/routers/access/interfaces/nm/hardware/installation/guide/ConntSer.html | title=Serial Network Modules }}</ref>

=== Access, core and distribution ===
[[File:OpenWRT 8.09.1 LuCI screenshot.png|thumb|A screenshot of the LuCI web interface used by [[OpenWrt]]. This page configures [[Dynamic DNS]].]]
The [[hierarchical internetworking model]] divides [[enterprise network]]s into three layers: core, distribution, and access.

Access routers, including [[small office/home office]] (SOHO) models, are located at home and customer sites such as branch offices that do not need [[hierarchical routing]] of their own. Typically, they are optimized for low cost. Some SOHO routers are capable of running alternative free Linux-based firmware like [[Tomato (firmware)|Tomato]], [[OpenWrt]], or [[DD-WRT]].<ref>{{Cite web|title=SOHO Network Requirements Planning and Implementation|url=https://www.examcollection.com/certification-training/network-plus-soho-network-requirements-planning-and-implementation.html|access-date=2021-03-25|website=ExamCollection|language=en}}</ref>

Distribution routers aggregate traffic from multiple access routers. Distribution routers are often responsible for enforcing quality of service across a [[wide area network]] (WAN), so they may have considerable memory installed, multiple WAN interface connections, and substantial onboard data processing routines. They may also provide connectivity to groups of file servers or other external networks.<ref>{{Cite web|date=2021-02-25|title=How Do WiFi Extenders Work? Repeater, Booster, Extender?|url=https://ispfamily.com/how-do-wifi-extenders-work/|access-date=2021-03-25|website=ISP Family|language=en-US}}</ref>

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. They tend to be optimized for high bandwidth but lack some of the features of edge routers.<ref>{{Cite web|title=Hierarchical Network Design Overview (1.1) > Cisco Networking Academy Connecting Networks Companion Guide: Hierarchical Network Design {{!}} Cisco Press|url=https://www.ciscopress.com/articles/article.asp?p=2202410&seqNum=4|access-date=2021-03-21|website=www.ciscopress.com}}</ref>

=== Security ===
External networks must be carefully considered as part of the overall security strategy of the local network. A router may include a [[Firewall (computing)|firewall]], [[VPN]] handling, and other security functions, or they may be handled by separate devices. Routers also commonly perform [[network address translation]] which restricts connections initiated from external connections but is not recognized as a security feature by all experts.<ref>{{cite web|url=http://www.safecomputing.umich.edu/protect-personal/download/nat_security.pdf|title=Security Considerations Of NAT|publisher=University of Michigan|archive-url=https://web.archive.org/web/20141018184244/http://www.safecomputing.umich.edu/protect-personal/download/nat_security.pdf|archive-date=October 18, 2014}}</ref> Some experts argue that [[Open-source software|open source]] routers are more secure and reliable than [[closed source]] routers because errors and potentially exploitable [[Vulnerability (computing)|vulnerabilities]] are more likely to be discovered and addressed in an open-source environment.<ref>{{cite press release|url=http://www.businesswire.com/news/home/20151014005564/en|title=Global Internet Experts Reveal Plan for More Secure, Reliable Wi-Fi Routers - and Internet|date=14 October 2015|url-status=live|archive-url=https://web.archive.org/web/20151020003515/http://www.businesswire.com/news/home/20151014005564/en|archive-date=2015-10-20}}</ref><ref>{{Cite web |date=2010-07-26 |title=Is Open Source Software More Secure than Proprietary Products? |url=https://www.govtech.com/security/Is-Open-Source-Software-More-Secure.html |access-date=2024-03-30 |website=GovTech |language=en}}</ref>

=== Routing different networks ===
Routers are also often distinguished on the basis of the network in which they operate. A router in a [[local area network]] (LAN) of a single organization is called an ''interior router''. A router that is operated in the [[Internet]] backbone is described as ''exterior router''. While a router that connects a LAN with the Internet or a [[wide area network]] (WAN) is called a ''border router'', or ''[[gateway router]]''.<ref>{{Cite book|title= Network+ Guide to Networks|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn=  9781423902454|pages=272}}</ref>

=== 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.

===Wi-Fi routers===
{{main|Wireless router}}
Wi-Fi routers combine the functions of a router with those of a [[wireless access point]]. They are typically devices with a small form factor, operating on the standard electric power supply for residential use. Connected to the Internet as offered by an [[Internet service provider]], they provide Internet access through a [[wireless network]] for home or office use.