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This article is about a computer networking device. For the kind of rotating cutting tool, see wood router. A router is a Woodworking Tool used to rout out (hollow out an area in the face of a piece of Wood. For the type of network router found in many homes, see residential gateway. This article is about the types of network routers and modems found in many homes known colloquially as "residential gateways" For the software used in electronic design automation, see routing (EDA). Electronic design automation ( EDA) is the category of tools for designing and producing electronic systems ranging from
Cisco 1800 Router
Cisco 1800 Router
Nortel ERS 8600
Nortel ERS 8600
Cisco 7600 Routers
Cisco 7600 Routers

A router (pronounced /'rautər/ in the USA and Australia, and pronounced /'ru:tər/ in the UK) is a computer whose software and hardware are usually tailored to the tasks of routing and forwarding information. Modules CPU Modules 8692SF Switch Fabric and CPU 8692 with Expansion Mezzanine card Supports 50 ms fail-over on trunks with MultiLink Trunking SMLT A computer is a Machine that manipulates data according to a list of instructions. Routing is the process of selecting paths in a network along which to send network traffic Routers generally contain a specialized operating system (e. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination g. Cisco's IOS or Juniper Networks JUNOS and JUNOSe or Extreme Networks XOS), RAM, NVRAM, flash memory, and one or more processors. Cisco IOS (originally Internetwork Operating System) is the software used on the vast majority of Cisco Systems Routers and all current Cisco Network Juniper Networks, Inc ( is an Information technology company based in Sunnyvale California and founded in 1996 Extreme Networks founded in 1996 is a publicly listed company that designs builds and installs Ethernet network solutions for enterprise and Carrier class Non-volatile Random access memory ( NVRAM) is the general name used to describe any type of random access memory which does not lose its information Flash memory is non-volatile computer memory that can be electrically erased and reprogrammed High-end routers contain many processors and specialized Application-specific integrated circuits (ASIC) and do a great deal of parallel processing. Parallel processing is also another term for Parallel computing. Chassis based systems like the Nortel MERS-8600 or ERS-8600 routing switch, (pictured right) have multiple ASICs on every module and allow for a wide variety of LAN, MAN, METRO, and WAN port technologies or other connections that are customizable. Nortel Networks Corporation () formerly known as Northern Telecom Limited and sometimes known simply as Nortel, is a multinational Telecommunications Modules CPU Modules 8692omSF Switch Fabric and CPU 8692 with Expansion Mezzanine card Supports 50 ms fail-over on NNI trunks with MultiLink Trunking Modules CPU Modules 8692SF Switch Fabric and CPU 8692 with Expansion Mezzanine card Supports 50 ms fail-over on trunks with MultiLink Trunking SMLT Metropolitan area network s or MAN s are large Computer networks usually spanning a city Wide Area Network ( WAN) is a Computer network that covers a broad area (i Much simpler routers are used where cost is important and the demand is low, for example in providing a home internet service. With appropriate software (such as Untangle, SmoothWall, XORP or Quagga), a standard PC can act as a router. Untangle is a privately held company that provides an Open source Network gateway for small businesses SmoothWall is a Linux distribution designed to be used as an Open source firewall. XORP, or E' x' tensible O pen R outer P latform is an Open source Routing software suite aimed at being both stable Quagga is a Network routing suite providing implementations of OSPF (v2 & v3 RIP (v1 v2 & v3 and BGP (v4 for Unix-like platforms

Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router. In Computer networks based on the Internet Protocol Suite, a subnetwork, or subnet, is a portion of the network's computers and network devices that have [1] The term layer 3 switch often is used interchangeably with router, but switch is really a general term without a rigorous technical definition. A In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types.

Routers operate in two different planes [2]:

Contents

Control Plane

Main article: Control Plane
Routers are like intersections whereas switches are like streets.
Routers are like intersections whereas switches are like streets. In Routing, the control plane is the part of the Router architecture that is concerned with drawing the network map or the information in a (possibly

Control Plane processing leads to the construction of what is variously called a routing table or routing information base (RIB). In Computer networking a routing table, or Routing Information Base (RIB, is an electronic table (file or database type object that is stored in a The RIB may be used by the Forwarding Plane to look up the outbound interface for a given packet, or, depending on the router implementation, the Control Plane may populate a separate Forwarding Information Base (FIB) with destination information. A Forwarding Information Base (FIB also known as a forwarding table, is most commonly used in network bridging, Routing, and similar functions to find RIBs are optimized for efficient updating with control mechanisms such as routing protocols, while FIBs are optimized for the fastest possible lookup of the information needed to select the outbound interface. A routing protocol is a protocol that specifies how Routers communicate with each other to disseminate information that allows them to select routes between any two

The Control Plane constructs the routing table from knowledge of the up/down status of its local interfaces, from hard-coded static routes, and from exchanging routing protocol information with other routers. Static routing describes a system that does not implement Adaptive routing. A routing protocol is a protocol that specifies how Routers communicate with each other to disseminate information that allows them to select routes between any two It is not compulsory for a router to use routing protocols to function, if for example it was configured solely with static routes. The routing table stores the best routes to certain network destinations, the "routing metrics" associated with those routes, and the path to the next hop router.

Routers do maintain state on the routes in the RIB/routing table, but this is quite distinct from not maintaining state on individual packets that have been forwarded. In Computer science and Automata theory, a state is a unique configuration of information in a program or machine

Forwarding Plane (a.k.a. Data Plane)

Main article: Forwarding Plane

For the pure Internet Protocol (IP) forwarding function, router design tries to minimize the state information kept on individual packets. In Routing, the forwarding plane defines the part of the Router architecture that decides what to do with packets arriving on an inbound interface The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol In Computer science and Automata theory, a state is a unique configuration of information in a program or machine Once a packet is forwarded, the router should no longer retain statistical information about it. It is the sending and receiving endpoints that keeps information about such things as errored or missing packets.

Forwarding decisions can involve decisions at layers other than the IP internetwork layer or OSI layer 3. Again, the marketing term switch can be applied to devices that have these capabilities. A function that forwards based on data link layer, or OSI layer 2, information, is properly called a bridge. A network bridge connects multiple Network segments at the Data link layer (layer 2 of the OSI model, and the term layer 2 switch is often Marketing literature may call it a layer 2 switch, but a switch has no precise definition.

Among the most important forwarding decisions is deciding what to do when congestion occurs, i. e. , packets arrive at the router at a rate higher than the router can process. Three policies commonly used in the Internet are Tail drop, Random early detection, and Weighted random early detection. Tail Drop, or Drop Tail is a simple queue management algorithm used by Internet Routers to decide when to drop packets Random early detection (RED also known as random early discard or random early drop is an active queue management Algorithm. Weighted random early detection (WRED is a queue management Algorithm with congestion avoidance capabilities Tail drop is the simplest and most easily implemented; the router simply drops packets once the length of the queue exceeds the size of the buffers in the router. Random early detection (RED) probabilistically drops datagrams early when the queue exceeds a configured size. Weighted random early detection requires a weighted average queue size to exceed the configured size, so that short bursts will not trigger random drops.

Types of routers

Cisco CRS-1 Carrier Routing System
Cisco CRS-1 Carrier Routing System
Linksys BEFSR41 DSL Router
Linksys BEFSR41 DSL Router

Routers may provide connectivity inside enterprises, between enterprises and the Internet, and inside Internet Service Providers (ISP). Carrier Routing System is a large-scale Core router, developed by Cisco Systems Inc An Internet service provider ( ISP, also called Internet access provider or IAP) is a company which primarily offers their customers access to the Internet The largest routers (for example the Cisco CRS-1 or Juniper T1600) interconnect ISPs, are used inside ISPs, or may be used in very large enterprise networks. Carrier Routing System is a large-scale Core router, developed by Cisco Systems Inc The smallest routers provide connectivity for small and home offices (for example the Linksys BEFSR41).

Routers for Internet connectivity and internal use

Routers intended for ISP and major enterprise connectivity will almost invariably exchange routing information with the Border Gateway Protocol. The Border Gateway Protocol ( BGP) is the core routing protocol of the Internet. RFC 4098[3] defines several types of BGP-speaking routers:

Within an ISP: Internal to the provider's AS, such a router speaks internal BGP (iBGP) to that provider's edge routers, other intra-provider core routers, or the provider's inter-provider border routers.
"Internet backbone:" The Internet does not have a clearly identifiable backbone, as did its predecessors. See default-free zone (DFZ). In the context of Internet Routing, the default-free zone (DFZ refers to both the collection of all Internet Autonomous systems that do not require a Nevertheless, it is the major ISPs' routers that make up what many would consider the core. These ISPs operate all four types of the BGP-speaking routers described here. In ISP usage, a "core" router is internal to an ISP, and 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 Multi-Protocol Label Switching (MPLS)[4]. MPLS redirects here For other uses see Mpls In Computer networking and Telecommunications, Multi Protocol Label Switching

Small Office Home Office (SOHO) connectivity

Main article: Residential gateway

Residential gateways (often called routers) are frequently used in homes to connect to a broadband service, such as IP over cable or DSL. This article is about the types of network routers and modems found in many homes known colloquially as "residential gateways" A cable is one or more Wires or Optical fibers bound together typically in a common protective jacket or sheath A home router may allow connectivity to an enterprise via a secure Virtual Private Network.

While functionally similar to routers, residential gateways use network address translation instead of routing. In Computer networking network address translation (NAT is the process of modifying Network address information in datagram packet headers while in transit across Instead of connecting local computers to the remote network directly, a residential gateway must make local computers appear to be a single computer.

Enterprise Routers

All sizes of routers may be found inside enterprises. While the most powerful routers tend to be found in ISPs, academic and research facilities, as well as large businesses, may need large routers.

A three-layer model is in common use, not all of which need be present in smaller networks [5].

Access

Access routers, including SOHO, are located at customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost.

Distribution

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. Distribution routers often are responsible for enforcing quality of service across a WAN, so they may have considerable memory, multiple WAN interfaces, and substantial processing intelligence.

They may also provide connectivity to groups of servers or to external networks. In the latter application, the router's functionality must be carefully considered as part of the overall security architecture. Separate from the router may be a Firewall or VPN concentrator, or the router may include these and other security functions. A firewall is an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system

When an enterprise is primarily on one campus, there may not be a distinct distribution tier, other than perhaps off-campus access. In such cases, the access routers, connected to LANs, interconnect via core routers.

Core

In enterprises, core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. This article is about a computer router used on the Internet backbone They tend to be optimized for high bandwidth.

When an enterprise is widely distributed with no central location(s), the function of core routing may be subsumed by the WAN service to which the enterprise subscribes, and the distribution routers become the highest tier.

History

The very first device that had fundamentally the same functionality as a router does today, i. e a packet switch, was the Interface Message Processor (IMP); IMPs were the devices that made up the ARPANET, the first packet switching network. A packet switch is a node used to build a network which utilizes the Packet switching paradigm for data communication The Interface Message Processor (IMP was the Packet-switching node used to connect computers to the original ARPANET in the late 1960s and 1970s The ARPANET ( Advanced Research Projects Agency Network) developed by ARPA of the United States Department of Defense, was the world's first operational Packet switching is a network communications method that splits data traffic (digital representations of text sound or video data into chunks called packets, that are then The idea for a router (although they were called "gateways" at the time) initially came about through an international group of computer networking researchers called the International Network Working Group (INWG). Set up in 1972 as an informal group to consider the technical issues involved in connecting different networks, later that year it became a subcommittee of the International Federation for Information Processing. The International Federation for Information Processing, usually known as IFIP, is an umbrella organization for national societies working in the field of Information technology [6]

These devices were different from most previous packet switches in two ways. First, they connected dissimilar kinds of networks, such as serial lines and local area networks. In Computing, a serial port is a Serial communication physical interface through which information transfers in or out one Bit at a time (contrast Second, they were connectionless devices, which had no role in assuring that traffic was delivered reliably, leaving that entirely to the hosts (although this particular idea had been previously pioneered in the CYCLADES network). In a packet-switched network connectionless mode transmission is a transmission in which each packet is prepended with a header containing a destination In Computer networking, a network host, Internet host or host is a Computer connected to the Internet. The CYCLADES Packet switching network was an extremely influential French network system in the early 1970s similar to the ARPANET.

The idea was explored in more detail, with the intention to produce real prototype system, as part of two contemporaneous programs. One was the initial DARPA-initiated program, which created the TCP/IP architecture of today. The Defense Advanced Research Projects Agency (DARPA is an agency of the United States Department of Defense responsible for the development of new Technology The Internet Protocol Suite (commonly TCP/IP) is the set of Communications protocols used for the Internet and other similar networks [7] The other was a program at Xerox PARC to explore new networking technologies, which produced the PARC Universal Packet system, although due to corporate intellectual property concerns it received little attention outside Xerox until years later. PARC (Palo Alto Research Center Inc formerly Xerox PARC, is a Research and development company in Palo Alto California that began as a division of The PARC Universal Packet (commonly abbreviated to PUP, although the original documents usually use Pup) was one of the two earliest Internetwork Protocol [8]

The earliest Xerox routers came into operation sometime after early 1974. The first true IP router was developed by Virginia Strazisar at BBN, as part of that DARPA-initiated effort, during 1975-1976. By the end of 1976, three PDP-11-based routers were in service in the experimental prototype Internet. The PDP-11 was a series of 16-bit Minicomputers sold by Digital Equipment Corp [9]

The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981; the Stanford router was done by William Yeager, and the MIT one by Noel Chiappa; both were also based on PDP-11s. Leland Stanford Junior University, commonly known as Stanford University or simply Stanford, is a private Research university located in William "Bill" Yeager (born June 16 1940, San Francisco) is an American Engineer. [10] [11] [12] [13]

As virtually all networking now uses IP at the network layer, multiprotocol routers are largely obsolete, although they were important in the early stages of the growth of computer networking, when several protocols other than TCP/IP were in widespread use. Routers that handle both IPv4 and IPv6 arguably are multiprotocol, but in a far less variable sense than a router that processed AppleTalk, DECnet, IP, and Xerox protocols.

In the original era of routing (from the mid-1970s through the 1980s), general-purpose mini-computers served as routers. This article is about the Decade 1970-1979 For the Year 1970 see 1970. The 1980s was the decade spanning from January 1 1980 to December 31 1989. A minicomputer (colloquially mini) is a class of multi-user Computers that lies in the middle range of the computing spectrum in between the largest Multi-user Although general-purpose computers can perform routing, modern high-speed routers are highly specialized computers, generally with extra hardware added to accelerate both common routing functions such as packet forwarding and specialised functions such as IPsec encryption. Internet Protocol Security ( IPsec) is a suite of protocols for securing Internet Protocol (IP communications by authenticating and/or encrypting

Still, there is substantial use of Linux and Unix machines, running open source routing code, for routing research and selected other applications. Linux (commonly pronounced ˈlɪnəks Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer While Cisco's operating system was independently designed, other major router operating systems, such as those from Juniper Networks and Extreme Networks, are extensively modified but still have Unix ancestry. Juniper Networks, Inc ( is an Information technology company based in Sunnyvale California and founded in 1996 Extreme Networks founded in 1996 is a publicly listed company that designs builds and installs Ethernet network solutions for enterprise and Carrier class

See also

External links

References

  1. ^ Requirements for IPv4 Routers,RFC 1812, F. This article is about a computer router used on the Internet backbone This article is about the types of network routers and modems found in many homes known colloquially as "residential gateways" A wireless router is a network device that performs the functions of a Router but also includes the functions of a Wireless access point. A wireless bridge is a hardware component used to connect two or more Network segments (LANs or parts of a LAN which are physically separated In Computer networking, a wireless access point ( WAP or AP) is a device that allows wireless communication devices to connect to a Wireless network In Computer networking and Telecommunications, route flapping occurs when a Router alternately advertises a destination network via one route then another In Electronics, a multiplexer or mux ( occasionally the term muldex is also found for a combination multiplexer-demultiplexer Prior to the widespread internetworking that led to the Internet most communication networks were limited by their nature to only allow communications between the stations on the network and In Computer networking network address translation (NAT is the process of modifying Network address information in datagram packet headers while in transit across A network bridge connects multiple Network segments at the Data link layer (layer 2 of the OSI model, and the term layer 2 switch is often A TR-069 (short for Technical Report 069 is a DSL Forum (which was later renamed as Broadband Forum technical specification entitled CPE WAN Management Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used Baker,June 1995
  2. ^ Requirements for Separation of IP Control and Forwarding,RFC 3654, H. Year 1995 ( MCMXCV) was a Common year starting on Sunday. Events of 1995 Khosravi & T. Anderson,November 2003
  3. ^ Terminology for Benchmarking BGP Device Convergence in the Control Plane,RFC 4098, H. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Berkowitz et al. ,June 2005
  4. ^ BGP/MPLS VPNs,RFC 2547, E. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Rosen and Y. Rekhter,April 2004
  5. ^ Oppenheimer, Priscilla (2004). "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Top-Down Network Design. Indianapolis: Cisco Press. ISBN 1587051524.  
  6. ^ Davies, Shanks, Heart, Barker, Despres, Detwiler, and Riml, "Report of Subgroup 1 on Communication System", INWG Note #1.
  7. ^ Vinton Cerf, Robert Kahn, "A Protocol for Packet Network Intercommunication", IEEE Transactions on Communications, Volume 22, Issue 5, May 1974, pp. 637 - 648.
  8. ^ David Boggs, John Shoch, Edward Taft, Robert Metcalfe, "Pup: An Internetwork Architecture", IEEE Transactions on Communications, Volume 28, Issue 4, April 1980, pp. 612- 624.
  9. ^ Craig Partridge, S. Blumenthal, "Data networking at BBN"; IEEE Annals of the History of Computing, Volume 28, Issue 1; January-March 2006.
  10. ^ Valley of the Nerds: Who Really Invented the Multiprotocol Router, and Why Should We Care?, Public Broadcasting Service, Accessed August 11, 2007. Events 2492 BC - Traditional date of the defeat of Bel by Hayk, progenitor and founder of the Armenian nation Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  11. ^ Router Man, NetworkWorld, Accessed June 22, 2007. Events 217 BC - Battle of Raphia: Ptolemy IV of Egypt defeats Antiochus III the Great of the Seleucid kingdom. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  12. ^ David D. Clark, "M. I. T. Campus Network Implementation", CCNG-2, Campus Computer Network Group, M. I. T. , Cambridge, 1982; pp. 26.
  13. ^ Pete Carey, "A Start-Up's True Tale: Often-told story of Cisco's launch leaves out the drama, intrigue", San Jose Mercury News, December 1, 2001.
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