Jumat, 10 Desember 2010


Router

From Wikipedia, the free encyclopedia
This article is about the computer networking device. For the rotating cutting tool, see Router (woodworking). For the variety of network devices found in household network setups, see residential gateway. For the software used in electronic design automation, see routing (electronic design automation).
This article may be confusing or unclear to readers. Please help clarify the article; suggestions may be found on the talk page.(May 2009)
A Cisco ASM/2-32EM router deployed atCERN in 1987.
Juniper SRX210 service gateway router
A router is an electronic device that intercepts signals on a computer network. The router determines where the signals have to go. Each signal it receives is called a data packet. The packet contains address information that the router uses to divert signals appropriately.

Contents

 [hide]

[edit]Application

When multiple routers are used in a large collection of interconnected networks, the routers exchange information, so that each router can build up a reference table showing the preferred paths between any two systems on the interconnected networks.
A router can have many interface connections, for different physical types of network (such as copper cables, fiber optic, or wireless transmission). It may contain firmware for different networking protocol standards. Each network interface device is specialized to convert computer signals from one protocol standard to another.
Two small computer networks connected with HUBS, these are not ROUTERS, but simply connectors between computers. SWITCHES may be used to connect HUBS together to help transfer signals more efficently between groups of users.
Routers can be used to connect two or more logical subnets, each having a different network address. The subnets addresses in the router do not necessarily map directly to the physical interfaces of the router.[1] The term "layer 3 switching" is often used interchangeably with the term "routing". The term switching is generally used to refer to data forwarding between two network devices with the same network address. This is also called layer 2 switching or LAN switching.
Conceptually, a router operates in two operational planes (or sub-systems):[2]
How a switch makes a direct signal exchange connection between only the two required computers.
  • Control plane: where a router builds an address table (called routing table) that records where a packet should be forwarded, and through which physical interface.It does this by using either statically configured statements (called static routes), or alternatively, by exchanging information with other routers in the network through a dynamical routing protocol.
  • Forwarding plane: The router actually forwards traffic, (called data packets in Internet Protocol language) from incoming interfaces to outgoing interfaces destination addresses that the packetheader contains. It performs this function by following rules derived from the routing table that has been recorded in the control plane.

[edit]Types of routers

A typical home router showing the ADSL telephone line and ETHERNET network cable connections.
Routers may provide connectivity inside enterprises, between enterprises and the Internet, and inside internet service providers (ISPs). 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. The smallest routers provide connectivity for small and home offices.

[edit]Routers for Internet connectivity and internal use

Routers intended for ISP and major enterprise connectivity almost invariably exchange routing information using the Border Gateway Protocol(BGP). RFC 4098[3] defines several types of BGP-speaking routers according to the routers' functions:
  • Edge router (ER): An ER is placed at the edge of an ISP network. The router speaks external BGP (EBGP) to a BGP speaker in another provider or large enterprise Autonomous System(AS). This type of router is also called PE (Provider Edge) routers.
  • Subscriber edge router (SER): An SER is located at the edge of the subscriber's network, it speaks EBGP to its provider's AS(s). It belongs to an end user (enterprise) organization. This type of router is also called CE (Customer Edge) routers.
  • Inter-provider border router: Interconnecting ISPs, this is a BGP-speaking router that maintains BGP sessions with other BGP speaking routers in other providers' ASes.
  • Core router: A core router is one that resides within an AS as back bone to carry traffic between edge 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). Nevertheless, the major ISPs' routers 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]
Routers are also used for port forwarding for private servers.

[edit]History

Leonard Kleinrock and the first IMP.
Avaya ERS 8600 (2010)
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. 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.[5]
These devices were different from most previous packet switches in two ways. First, they connected dissimilar kinds of networks, such asserial lines and local area networks. 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).
The idea was explored in more detail, with the intention to produce a real prototype system, as part of two contemporaneous programs. One was the initial DARPA-initiated program, which created the TCP/IP architecture of today.[6] 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.[7]
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.[8]
The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981; the Stanford router was done byWilliam Yeager, and the MIT one by Noel Chiappa; both were also based on PDP-11s.[9][10][11][12]
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. 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.
Still, there is substantial use of Linux and Unix machines, running open source routing code, for routing research and other applications. WhileCisco's operating system was independently designed, other major router operating systems, such as those from Juniper Networks andExtreme Networks, are extensively modified but still have Unix ancestry.

[edit]Enterprise routers

All sizes of routers may be found inside enterprises. The most powerful routers tend to be found in ISPs and academic & research facilities. Large businesses may also need powerful routers.
A three-layer model is in common use, not all of which need be present in smaller networks.[13]

[edit]Access

Linksys by Cisco WRT54GL SoHo Router
A screenshot of the LuCI web interface used by OpenWrt. Here it is being used to configure Dynamic DNS.
Access routers, including 'small office/home office' (SOHO) models, are located at customer sites such as branch offices that do not needhierarchical routing of their own. Typically, they are optimized for low cost. Some SOHO routers are capable of running alternative free Linux-based firmwares like OpenWrt.

[edit]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.

[edit]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. They tend to be optimized for high bandwidth.

[edit]Forwarding plane (a.k.a. data plane)

Main article: Forwarding plane
For pure Internet Protocol (IP) forwarding function, a router is designed to minimize the state information on individual packets. The main purpose of a router is to connect multiple networks and forward packets destined either for its own networks or other networks. A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. This process is known as routing. When each router receives a packet, it searches its routing table to find the best match between the destination IP address of the packet and one of the network addresses in the routing table. Once a match is found, the packet is encapsulated in the layer 2 data link frame for that outgoing interface. A router does not look into the actual data contents that the packet carries, but only at the layer 3 addresses to make a forwarding decision, plus optionally other information in the header for hint on, for example, QoS. Once a packet is forwarded, the router does not retain any historical information about the packet, but the forwarding action can be collected into the statistical data, if so configured.
Forwarding decisions can involve decisions at layers other than the IP internetwork layer or OSI layer 3. A function that forwards based on data link layer, or OSI layer 2, information, is properly called a bridge or switch. This function is referred to as layer 2 switching, as the addresses it uses to forward the traffic are layer 2 addresses in the OSI layer model.
Besides making decision as which interface a packet is forwarded to, which is handled primarily via the routing table, a router also has to manage congestion, when packets arrive 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 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 is exceeds a pre-configured size of the queue until a pre-configured max when it becomes tail drop. Weighted random early detection requires a weight on the average queue size to act upon when the traffic is about to exceed the pre-configured size, so that short bursts will not trigger random drops.
Another function a router performs is to decide which packet should be processed first when multiple queues exist. This is managed through Quality of service (QoS), which is critical when VoIP (Voice over IP) is deployed, so that delays between packets do not exceed 150ms to maintain the quality of voice conversations.
Yet another function a router performs is called "policy based routing" where special rules are constructed to override the rules derived from the routing table when a packet forwarding decision is made.
These functions may be performed through the same internal paths that the packets travel inside the router. Some of the functions may be performed through an application-specific integrated circuit (ASIC) to avoid overhead caused by multiple CPU cycles, and others may have to be performed through the CPU as these packets need special attention that cannot be handled by an ASIC.

[edit]References

Router

Dari Wikipedia bahasa Indonesia, ensiklopedia bebas
Router Wi-Fi D-Link
Router adalah sebuah alat jaringan komputer yang mengirimkan paket data melalui sebuah jaringan atau Internet menuju tujuannya, melalui sebuah proses yang dikenal sebagai routing. Proses routing terjadi pada lapisan 3 (Lapisan jaringan seperti Internet Protocol) dari stack protokol tujuh-lapis OSI.

Daftar isi

 [sembunyikan]

[sunting]Fungsi

Router berfungsi sebagai penghubung antar dua atau lebih jaringan untuk meneruskan data dari satu jaringan ke jaringan lainnya. Router berbeda dengan switch. Switch merupakan penghubung beberapa alat untuk membentuk suatu Local Area Network (LAN).
Analogi Router dan Switch
Sebagai ilustrasi perbedaan fungsi dari router dan switch merupakan suatu jalanan, dan router merupakan penghubung antar jalan. Masing-masing rumah berada pada jalan yang memiliki alamat dalam suatu urutan tertentu. Dengan cara yang sama, switch menghubungkan berbagai macam alat, dimana masing-masing alat memiliki alamat IP sendiri pada sebuah LAN.
Router sangat banyak digunakan dalam jaringan berbasis teknologi protokol TCP/IP, dan router jenis itu disebut juga dengan IP Router. Selain IP Router, ada lagi AppleTalk Router, dan masih ada beberapa jenis routerlainnya. Internet merupakan contoh utama dari sebuah jaringan yang memiliki banyak router IP. Router dapat digunakan untuk menghubungkan banyak jaringan kecil ke sebuah jaringan yang lebih besar, yang disebut dengan internetwork, atau untuk membagi sebuah jaringan besar ke dalam beberapa subnetwork untuk meningkatkan kinerja dan juga mempermudah manajemennya. Router juga kadang digunakan untuk mengoneksikan dua buah jaringan yang menggunakan media yang berbeda (seperti halnya router wireless yang pada umumnya selain ia dapat menghubungkan komputer dengan menggunakan radio, ia juga mendukung penghubungan komputer dengan kabel UTP), atau berbeda arsitektur jaringan, seperti halnya dari Ethernet keToken Ring.
Router juga dapat digunakan untuk menghubungkan LAN ke sebuah layanan telekomunikasi seperti halnyatelekomunikasi leased line atau Digital Subscriber Line (DSL). Router yang digunakan untuk menghubungkan LAN ke sebuah koneksi leased line seperti T1, atau T3, sering disebut sebagai access server. Sementara itu, router yang digunakan untuk menghubungkan jaringan lokal ke sebuah koneksi DSL disebut juga dengan DSL router. Router-router jenis tersebut umumnya memiliki fungsi firewall untuk melakukan penapisan paket berdasarkan alamat sumber dan alamat tujuan paket tersebut, meski beberapa router tidak memilikinya. Router yang memiliki fitur penapisan paket disebut juga dengan packet-filtering router. Router umumnya memblokir lalu lintas data yang dipancarkan secara broadcast sehingga dapat mencegah adanya broadcast storm yang mampu memperlambat kinerja jaringan.

[sunting]Jenis-jenis router

Secara umum, router dibagi menjadi dua buah jenis, yakni:
  • static router (router statis): adalah sebuah router yang memiliki tabel routing statis yang di setting secara manual oleh para administrator jaringan.
  • dynamic router (router dinamis): adalah sebuah router yang memiliki dab membuat tabel routing dinamis, dengan mendengarkan lalu lintas jaringan dan juga dengan saling berhubungan dengan router lainnya.

[sunting]Router versus Bridge

Cara kerja router mirip dengan bridge jaringan, yakni mereka dapat meneruskan paket data jaringan dan dapat juga membagi jaringan menjadi beberapa segmen atau menyatukan segmen-segmen jaringan. Akan tetapi, router berjalan pada lapisan ketiga pada model OSI (lapisan jaringan), dan menggunakan skema pengalamatan yang digunakan pada lapisan itu, seperti halnya alamat IP. Sementara itu, bridge jaringan berjalan pada lapisan kedua pada model OSI (lapisan data-link), dan menggunakan skema pengalamatan yang digunakan pada lapisan itu, yakni MAC address.
Lalu, kapan penggunaan bridge jaringan dilakukan dan kapan penggunakan router dilakukan? Bridge, sebaiknya digunakan untuk menghubungkan segmen-segmen jaringan yang menjalankan protokol jaringan yang sama (sebagai contoh: segmen jaringan berbasis IP dengan segmen jaringan IP lainnya). Selain itu, bridge juga dapat digunakan ketika di dalam jaringan terdapat protokol-protokol yang tidak bisa melakukan routing, seperti halnya NetBEUI. Sementara itu, router sebaiknya digunakan untuk menghubungkan segmen-segmen jaringan yang menjalankan protokol jaringan yang berebeda (seperti halnya untuk menghubungkan segmen jaringan IP dengan segmen jaringan IPX.) Secara umum, router lebih cerdas dibandingkan dengan bridge jaringan dan dapat meningkatkan bandwidth jaringan, mengingat router tidak meneruskan paket broadcast ke jaringan yang dituju. Dan, penggunaan routeryang paling sering dilakukan adalah ketika kita hendak menghubungkan jaringan kita ke internet.

[sunting]Produsen router

Beberapa produsen router termasuk:

[sunting]Lihat pula

[sunting]Pranala luar

Diposting oleh di

Tidak ada komentar:

Posting Komentar

Langganan: Posting Komentar (Atom)