Network switch

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Avaya ERS 2550T-PWR, a 50-port Ethernet switch 2550T-PWR-Front.jpg
Avaya ERS 2550T-PWR, a 50-port Ethernet switch

A network switch (also called switching hub, bridging hub, and, by the IEEE, MAC bridge [1] ) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device.

Contents

A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer (layer 2) of the OSI model. Some switches can also forward data at the network layer (layer 3) by additionally incorporating routing functionality. Such switches are commonly known as layer-3 switches or multilayer switches. [2]

Switches for Ethernet are the most common form of network switch. The first MAC Bridge [3] [4] [5] was invented [6] in 1983 by Mark Kempf, an engineer in the Networking Advanced Development group of Digital Equipment Corporation. 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 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. [7] 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, Asynchronous Transfer Mode, 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. [8]

Overview

Cisco small business SG300-28 28-port Gigabit Ethernet rackmount switch.jpg
Internals of a Cisco small business SG300-28 28-port Gigabit Ethernet rackmount switch.jpg
Cisco small business SG300-28 28-port Gigabit Ethernet rackmount switch and its internals

A switch is a device in a computer network 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 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 (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. [lower-alpha 1] 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 networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose device such as a residential gateway to access small office/home broadband 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 (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, RapidIO, ATM, ITU-T 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. [10] Devices that interconnect at the layer 3 are traditionally called routers. [11]

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, [12] [13] network intrusion detection, [14] and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules. [15]

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

A modular network switch with three network modules (a total of 24 Ethernet and 14 Fast Ethernet ports) and one power supply. Smartswitch6000.jpg
A modular network switch with three network modules (a total of 24 Ethernet and 14 Fast Ethernet ports) and one power supply.
A 5-port layer-2 switch without management functionality 5 Port Gigabit Netzwerk-Switch TL-SG1005D 01.jpg
A 5-port layer-2 switch without management functionality

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 uplinks 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 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. [16] [17]

Types

A rack-mounted 24-port 3Com switch 24-port 3Com switch.JPG
A rack-mounted 24-port 3Com switch

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; 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 switches or large chassis units with swappable line cards.

Configuration options

Typical management features

A couple of managed D-Link Gigabit Ethernet rackmount switches, connected to the Ethernet ports on a few patch panels using Category 6 patch cables (all equipment is installed in a standard 19-inch rack) 19-inch rackmount Ethernet switches and patch panels.jpg
A couple of managed D-Link Gigabit Ethernet rackmount switches, connected to the Ethernet ports on a few patch panels using Category 6 patch cables (all equipment is installed in a standard 19-inch rack)

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:

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. [21]

See also

Notes

  1. In half duplex mode, each switch port can only either receive from or transmit to its connected device at a certain time. In full duplex mode, each switch port can simultaneously transmit and receive, assuming the connected device also supports full-duplex mode. [9]

Related Research Articles

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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 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.

Ethernet over twisted pair Ethernet physical layers using twisted-pair cables

Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.

Network topology Arrangement of the elements of a communication network

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The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Spanning tree also allows a network design to include backup links providing fault tolerance if an active link fails.

A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer. In this context, virtual, refers to a physical object recreated and altered by additional logic, within the local area network. VLANs work by applying tags to network frames and handling these tags in networking systems – creating the appearance and functionality of network traffic that is physically on a single network but acts as if it is split between separate networks. In this way, VLANs can keep network applications separate despite being connected to the same physical network, and without requiring multiple sets of cabling and networking devices to be deployed.

Medium access control Service layer in IEEE 802 network standards

In IEEE 802 LAN/MAN standards, the medium access control sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer. Within the data link layer, the LLC provides flow control and multiplexing for the logical link, while the MAC provides flow control and multiplexing for the transmission medium.

Cisco Discovery Protocol (CDP) is a proprietary Data Link Layer protocol developed by Cisco Systems in 1994 by Keith McCloghrie and Dino Farinacci. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address. CDP can also be used for On-Demand Routing, which is a method of including routing information in CDP announcements so that dynamic routing protocols do not need to be used in simple networks.

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Ethernet hub Device for interconnecting Ethernet devices

An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer of the OSI model. A repeater hub also participates in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.

Link aggregation Using multiple network connections in parallel to increase capacity and reliability

In computer networking, link aggregation is the combining of multiple network connections in parallel by any of several methods, in order to increase throughput beyond what a single connection could sustain, to provide redundancy in case one of the links should fail, or both. A link aggregation group (LAG) is the combined collection of physical ports.

Ethernet flow control Technique to suspend transmission to avoid congestion

Ethernet flow control is a mechanism for temporarily stopping the transmission of data on Ethernet family computer networks. The goal of this mechanism is to avoid packet loss in the presence of network congestion.

Network bridge Device that creates a larger computer network from two smaller networks

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The Link Layer Discovery Protocol (LLDP) is a vendor-neutral link layer protocol used by network devices for advertising their identity, capabilities, and neighbors on a local area network based on IEEE 802 technology, principally wired Ethernet. The protocol is formally referred to by the IEEE as Station and Media Access Control Connectivity Discovery specified in IEEE 802.1AB with additional support in IEEE 802.3 section 6 clause 79.

Computer network Network that allows computers to share resources and communicate with each other

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On an Ethernet connection, a duplex mismatch is a condition where two connected devices operate in different duplex modes, that is, one operates in half duplex while the other one operates in full duplex. The effect of a duplex mismatch is a link that operates inefficiently. Duplex mismatch may be caused by manually setting two connected network interfaces at different duplex modes or by connecting a device that performs autonegotiation to one that is manually set to a full duplex mode.

Inter-network processors are special-purpose processors which aid in the interconnection of telecommunications networks. Most commonly used inter-network processors are switches, bridges, hubs, routers and gateways.

Data center bridging (DCB) is a set of enhancements to the Ethernet local area network communication protocol for use in data center environments, in particular for use with clustering and storage area networks.

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Audio Video Bridging Specifications for synchronized, low-latency streaming through IEEE 802 networks

Audio Video Bridging (AVB) is a common name for the set of technical standards which provide improved synchronization, low-latency, and reliability for switched Ethernet networks. AVB embodies the following technologies and standards:

References

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  13. Switch 8800 Firewall Module, 3Com Corporation, 2006
  14. Cisco Catalyst 6500 Series Intrusion Detection System (IDSM-2) Module, Cisco Systems,2007
  15. Getting Started with Check Point Fire Wall-1, Checkpoint Software Technologies Ltd., n.d.
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  21. "How to Build a Miniature Network Monitor Device". 6 October 2016. Retrieved 2019-01-08.