Network Switch
   HOME

TheInfoList



OR:

A network switch (also called switching hub, bridging hub, and, by the
IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operati ...
, MAC bridge) is
networking hardware Networking hardware, also known as network equipment or computer networking devices, are electronic devices which are required for communication and interaction between devices on a computer network. Specifically, they mediate data transmission in ...
that connects devices on a
computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections ar ...
by using
packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into ''network packet, packets'' that are transmitted over a digital Telecommunications network, network. Packets are made of a header (computing), header and ...
to receive and forward data to the destination device. A network switch is a multiport network bridge that uses
MAC address A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking tec ...
es to forward data at the
data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer ...
(layer 2) of the OSI model. Some switches can also forward data at the
network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of trans ...
(layer 3) by additionally incorporating
routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...
functionality. Such switches are commonly known as layer-3 switches or multilayer switches. Switches for
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in ...
are the most common form of network switch. The first MAC Bridge was invented in 1983 by Mark Kempf, an engineer in the Networking Advanced Development group of
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unti ...
. The first 2 port Bridge product (LANBridge 100) was introduced by that company shortly after. The company subsequently produced multi-port switches for both Ethernet and
FDDI Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case i ...
such as GigaSwitch. Digital decided to license its MAC Bridge patent in a royalty-free, non-discriminatory basis that allowed IEEE standardization. This permitted a number of other companies to produce multi-port switches, including Kalpana. Ethernet was initially a shared-access medium, but the introduction of the MAC bridge began its transformation into its most-common point-to-point form without a collision domain. Switches also exist for other types of networks including
Fibre Channel Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data c ...
,
Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs o ...
, and InfiniBand. Unlike repeater hubs, which broadcast the same data out of each port and let the devices pick out the data addressed to them, a network switch learns the identities of connected devices and then only forwards data to the port connected to the device to which it is addressed.


Overview

A switch is a device in a
computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections ar ...
that connects other devices together. Multiple data cables are plugged into a switch to enable communication between different networked devices. Switches manage the flow of data across a network by transmitting a received
network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the '' payload''. Control infor ...
only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address, allowing the switch to direct the flow of traffic maximizing the security and efficiency of the network. A switch is more intelligent than an Ethernet hub, which simply retransmits packets out of every port of the hub except the port on which the packet was received, unable to distinguish different recipients, and achieving an overall lower network efficiency. An Ethernet switch operates at the
data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer ...
(layer 2) of the OSI model to create a separate collision domain for each switch port. Each device connected to a switch port can transfer data to any of the other ports at any time and the transmissions will not interfere. Because broadcasts are still being forwarded to all connected devices by the switch, the newly formed network segment continues to be a broadcast domain. Switches may also operate at higher layers of the OSI model, including the network layer and above. A device that also operates at these higher layers is known as a multilayer switch. Segmentation involves the use of a switch to split a larger collision domain into smaller ones in order to reduce collision probability and to improve overall network throughput. In the extreme case (i.e. micro-segmentation), each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex mode. Full-duplex mode has only one transmitter and one receiver per collision domain, making collisions impossible. The network switch plays an integral role in most modern Ethernet
local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...
s (LANs). Mid-to-large sized LANs contain a number of linked managed switches.
Small office/home office Small office/home office (or single office/home office; sometimes short SOHO) refers to the category of business or cottage industry that involves from 1 to 10 workers. In New Zealand, the Ministry of Business, Innovation and Employment (MBI ...
(SOHO) applications typically use a single switch, or an all-purpose device such as a residential gateway to access small office/home
broadband In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...
services such as DSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for
Voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Interne ...
(VoIP).


Role in a network

Switches are most commonly used as the network connection point for hosts at the edge of a network. In the hierarchical internetworking model and similar network architectures, switches are also used deeper in the network to provide connections between the switches at the edge. In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet,
Fibre Channel Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data c ...
, RapidIO, ATM,
ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
G.hn and 802.11. This connectivity can be at any of the layers mentioned. While the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and Token Ring is performed more easily at layer 3 or via routing. Devices that interconnect at the layer 3 are traditionally called routers. Where there is a need for a great deal of analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall, network intrusion detection, and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules. Through port mirroring, a switch can create a mirror image of data that can go to an external device such as intrusion detection systems and packet sniffers. A modern switch may implement power over Ethernet (PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies, the connected device can continue operating even when regular office power fails.


Bridging

Modern commercial switches primarily use Ethernet interfaces. The core function of an Ethernet switch is to provide multiple ports of layer-2 bridging. Layer-1 functionality is required in all switches in support of the higher layers. Many switches also perform operations at other layers. A device capable of more than bridging is known as a multilayer switch. A layer 2 network device is a multiport device that uses hardware addresses ( MAC addresses) to process and forward data at the data link layer (layer 2). A switch operating as a network bridge may interconnect otherwise separate layer 2 networks. The bridge learns the MAC address of each connected device. Bridges also buffer an incoming packet and adapt the transmission speed to that of the outgoing port. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end-user access typically concentrates lower bandwidth and
uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...
s into a higher bandwidth. Interconnects between switches may be regulated using the spanning tree protocol (STP) that disables forwarding on links so that the resulting local area network is a
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
without switching loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. Shortest path bridging and TRILL (TRansparent Interconnection of Lots of Links) are layer 2 alternatives to STP which allow all paths to be active with multiple equal cost paths.


Types


Form factors

Switches are available in many form factors, including stand-alone, desktop units which are typically intended to be used in a home or office environment outside a wiring closet; rack-mounted switches for use in an equipment rack or an
enclosure Enclosure or Inclosure is a term, used in English landownership, that refers to the appropriation of "waste" or " common land" enclosing it and by doing so depriving commoners of their rights of access and privilege. Agreements to enclose land ...
; DIN rail mounted for use in industrial environments; and small installation switches, mounted into a cable duct, floor box or communications tower, as found, for example, in fiber to the office infrastructures. Rack-mounted switches may be standalone units,
stackable switch A stackable switch is a network switch that is fully functional operating standalone but which can also be set up to operate together with one or more other network switches, with this group of switches showing the characteristics of a single swit ...
es or large chassis units with swappable line cards.


Configuration options

*Unmanaged switches have no configuration interface or options. They are plug and play. They are typically the least expensive switches, and therefore often used in a
small office/home office Small office/home office (or single office/home office; sometimes short SOHO) refers to the category of business or cottage industry that involves from 1 to 10 workers. In New Zealand, the Ministry of Business, Innovation and Employment (MBI ...
environment. Unmanaged switches can be desktop or rack mounted. *Managed switches have one or more methods to modify the operation of the switch. Common management methods include: a command-line interface (CLI) accessed via serial console, telnet or
Secure Shell The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based ...
, an embedded Simple Network Management Protocol (SNMP) agent allowing management from a remote console or management station, or a web interface for management from a
web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on ...
. Examples of configuration changes that one can do from a managed switch include: enabling features such as Spanning Tree Protocol or port mirroring, setting port bandwidth, creating or modifying VLANs (virtual LANs), etc. Two sub-classes of managed switches are smart and enterprise managed switches. *Smart switches (aka intelligent switches) are managed switches with a limited set of management features. Likewise, "web-managed" switches are switches that fall into a market niche between unmanaged and managed. For a price much lower than a fully managed switch they provide a web interface (and usually no CLI access) and allow configuration of basic settings, such as VLANs, port-bandwidth and duplex. *Enterprise managed switches (aka managed switches) have a full set of management features, including CLI, SNMP agent, and web interface. They may have additional features to manipulate configurations, such as the ability to display, modify, backup and restore configurations. Compared with smart switches, enterprise switches have more features that can be customized or optimized and are generally more expensive than smart switches. Enterprise switches are typically found in networks with a larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. A
stackable switch A stackable switch is a network switch that is fully functional operating standalone but which can also be set up to operate together with one or more other network switches, with this group of switches showing the characteristics of a single swit ...
is a type of an enterprise-managed switch.


Typical management features

* Enable and disable ports * Link bandwidth and
duplex Duplex (Latin, 'double') may refer to: Arts and entertainment * ''Duplex'' (film), or ''Our House'', a 2003 American black comedy film * Duplex (band), a Dutch electronic music duo * Duplex (Norwegian duo) * Duplex!, a Canadian children's music ...
settings *
Quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...
configuration and monitoring *
MAC filtering In computer networking, MAC address filtering is a security access control In the fields of physical security and information security, access control (AC) is the selective restriction of access to a place or other resource, while acces ...
and other access control list features * Configuration of Spanning Tree Protocol (STP) and Shortest Path Bridging (SPB) features * Simple Network Management Protocol (SNMP) monitoring of device and link health * Port mirroring for monitoring traffic and troubleshooting * Link aggregation configuration to set up multiple ports for the same connection to achieve higher data transfer rates and reliability * VLAN configuration and port assignments including IEEE 802.1Q tagging *
Network Access Control Network access control (NAC) is an approach to computer security that attempts to unify endpoint security technology (such as antivirus, host intrusion prevention, and vulnerability assessment), user or system authentication and network security ...
features such as IEEE 802.1X * IGMP snooping for control of multicast traffic


Traffic monitoring

It is difficult to monitor traffic that is bridged using a switch because only the sending and receiving ports can see the traffic. Methods that are specifically designed to allow a network analyst to monitor traffic include: * Port mirroring the switch sends a copy of network packets to a monitoring network connection. * SMON "Switch Monitoring" is described by RFC 2613 and is a protocol for controlling facilities such as port mirroring. * RMON *
sFlow sFlow, short for "sampled flow", is an industry standard for packet export at Layer 2 of the OSI model. sFlow was originally developed by InMon Corp. It provides a means for exporting truncated packets, together with interface counters for the purp ...
These monitoring features are rarely present on consumer-grade switches. Other monitoring methods include connecting a layer-1 hub or network tap between the monitored device and its switch port.


See also

* Console server * Energy-Efficient Ethernet * Fibre Channel switch * Fully switched network *
Load-balanced switch A load-balanced switch is a switch architecture which guarantees 100% throughput with no central arbitration at all, at the cost of sending each packet across the crossbar twice. Load-balanced switches are a subject of research for large routers ...
* Modular computer network switch * Packet switch *
Stackable switch A stackable switch is a network switch that is fully functional operating standalone but which can also be set up to operate together with one or more other network switches, with this group of switches showing the characteristics of a single swit ...
*
Telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...
* Turing switch *
Wide area network A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits. Businesses, as well as schools and government entities, u ...


Notes


References


External links


What to consider when buying an Ethernet Switch
{{DEFAULTSORT:Network Switch Ethernet
Switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type ...