Network switch
Encyclopedia
A network switch or switching hub is a computer networking device
that connects network segment
s.
The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer
(layer 2) of the OSI model
. Switches that additionally process data at the network layer
(Layer 3) and above are often referred to as Layer 3 switches or multilayer switch
es.
The first Ethernet
switch was introduced by Kalpana
in 1990.
local area network
s (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 converged 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 VoIP.
An Ethernet switch operates at the data link layer of the OSI model
to create a separate collision domain
for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, A and B can transfer data back and forth, while C and D also do so simultaneously, and the two conversations will not interfere with one another. In the case of a hub, they would all share the bandwidth and run in half duplex, resulting in collisions, which would then necessitate retransmissions. Using a switch is called microsegmentation
. This allows computers to have dedicated bandwidth on a point-to-point connections to the network and to therefore run in full duplex without collisions.
and network
. A device that operates simultaneously at more than one of these layers is known as a multilayer switch
.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet
, Fibre Channel
, ATM
, ITU-T
G.hn
and 802.11. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet
and token ring is easier at Layer 3.
Devices that interconnect at Layer 3 are traditionally called routers, so "Layer-3 switches" can also be regarded as (relatively primitive) routers.
In some service provider and other environments 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.
In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffer
s.
While switches may learn about topologies at many layers, and forward at one or more layers, they do tend to have common features. Other than for high-performance applications, modern commercial switches use primarily Ethernet interfaces, which can have different input and output bandwidths of 10, 100, 1000 or 10,000 megabits per second.
At any layer, 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.
is broadcast out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions
affect the entire network, limiting its capacity.
There are specialized applications where a hub can be useful, such as copying traffic to multiple network sensors. High end switches have a feature which does the same thing called port mirroring
.
By the early 2000s, there was little price difference between a hub and a low-end switch.
of each connected device.
Single bridges also can provide extremely high performance in specialized applications such as storage area networks.
Classic bridges may also interconnect using a spanning tree protocol
that disables links so that the resulting local area network is a tree
without loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. The older IEEE 802.1D
spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while the spanning tree would reconverge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w, but the newest edition of IEEE 802.1D
adopts the 802.1w extensions as the base standard.
The IETF is specifying the TRILL protocol, which is the application of link-state routing technology to the layer-2 bridging problem. Devices which implement TRILL, called RBridges
, combine the best features of both routers and bridges.
While "layer 2 switch" remains more of a marketing term than a technical term, the products that were introduced as "switches" tended to use microsegmentation
and Full duplex to prevent collisions among devices connected to Ethernet. By using an internal forwarding plane
much faster than any interface, they give the impression of simultaneous paths among multiple devices.
Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth method were performance-increasing methods when used on "switch" products with the same input and output port bandwidths:
While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is rarely the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth (e.g., 10/100 Mbit/s) into a higher bandwidth (at least 1 Gbit/s). Alternatively, a switch that provides access to server ports usually connects to them at a much higher bandwidth than is used by end user devices.
The most common layer-3 capability is awareness of IP multicast
through IGMP snooping
. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group.
, but then adds some type of load distribution
based on TCP
sessions.
The device may include a stateful firewall
, a VPN concentrator, or be an IPSec
security gateway.
or by some installation-specific technique to recognize application-level transactions. A Layer-7 switch may include a web cache
and participate in a content delivery network
.
or SMON are implemented in a switch, it is difficult to monitor traffic that is bridged using a switch because only the sending and receiving ports can see the traffic. These monitoring features are rarely present on consumer-grade switches.
Two popular methods that are specifically designed to allow a network analyst to monitor traffic are:
Another method to monitor may be to connect a Layer-1 hub between the monitored device and its switch port. This will induce minor delay, but will provide multiple interfaces that can be used to monitor the individual switch port.
Link aggregation
allows the use of multiple ports for the same connection achieving higher data transfer rates. Creating VLANs can serve security and performance goals by reducing the size of the broadcast domain
.
Computer networking device
'Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems or InterWorking Unit...
that connects network segment
Network segment
A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations.-Ethernet:...
s.
The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
(layer 2) of the OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
. Switches that additionally process data at the network layer
Network layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
(Layer 3) and above are often referred to as Layer 3 switches or multilayer switch
Multilayer switch
A multilayer switch is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers.- Layer 3 Switching :...
es.
The first Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
switch was introduced by Kalpana
Kalpana (company)
Kalpana was a computer networking equipment manufacturer, located in Silicon Valley during the 1980s and 1990s.Kalpana is considered to be the inventor of Ethernet switching as the company was the first to introduce the concept of a multi-port network switch with its seven-port EtherSwitch in 1990...
in 1990.
Function
The network switch plays an integral part in most modern EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
s (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office
Small office/home office
Small office/home office, or SOHO, refers to the category of business or cottage industry which involves from 1 to 10 workers. SOHO can also stand for single office/home office....
(SOHO) applications typically use a single switch, or an all-purpose converged device
Technological convergence
Technological convergence is the tendency for different technological systems to evolve towards performing similar tasks. Convergence can refer to previously separate technologies such as voice , data , and video that now share resources and interact with each other synergistically.The rise of...
such as a residential gateway
Residential gateway
A residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
to access small office/home broadband
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
services such as DSL
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
or cable internet
Cable internet
In telecommunications, cable Internet access, often shortened to cable Internet or simply cable, is a form of broadband Internet access that uses the cable television infrastructure. Like digital subscriber line and fiber to the premises services, cable Internet access provides network edge...
. 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 VoIP.
An Ethernet switch operates at the data link layer of the OSI model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
to create a separate collision domain
Collision domain
A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...
for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, A and B can transfer data back and forth, while C and D also do so simultaneously, and the two conversations will not interfere with one another. In the case of a hub, they would all share the bandwidth and run in half duplex, resulting in collisions, which would then necessitate retransmissions. Using a switch is called microsegmentation
Microsegmentation
Microsegmentation in computer networking is a term used to describe the segmentation of a collision domain into as many segments as there are circuits, minus one . This microsegmentation performed by the switch cuts the collision domain down so that only two nodes coexist within each collision domain...
. This allows computers to have dedicated bandwidth on a point-to-point connections to the network and to therefore run in full duplex without collisions.
Role of switches in networks
Switches may operate at one or more layers of the OSI model, including data linkData link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
and network
Network layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
. A device that operates simultaneously at more than one of these layers is known as a multilayer switch
Multilayer switch
A multilayer switch is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers.- Layer 3 Switching :...
.
In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
, Fibre Channel
Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
, ATM
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
, ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hn
G.hn
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
and 802.11. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
and token ring is easier at Layer 3.
Devices that interconnect at Layer 3 are traditionally called routers, so "Layer-3 switches" can also be regarded as (relatively primitive) routers.
In some service provider and other environments 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
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....
, network intrusion detection
Intrusion detection
In Information Security, intrusion detection is the act of detecting actions that attempt to compromise the confidentiality, integrity or availability of a resource. When Intrusion detection takes a preventive measure without direct human intervention, then it becomes an Intrusion-prevention...
, and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.
In other cases, the switch is used to create a mirror image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as intrusion detection systems and packet sniffer
Packet sniffer
A packet analyzer is a computer program or a piece of computer hardware that can intercept and log traffic passing over a digital network or part of a network...
s.
Layer-specific functionality
At any layer, a modern switch may implement power over Ethernet
Power over Ethernet
Power over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels...
(PoE), which avoids the need for attached devices, such as a VoIP phone or wireless access point
Wireless access point
In computer networking, a wireless access point is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards...
, to have a separate power supply. Since switches can have redundant power circuits connected to uninterruptible power supplies
Uninterruptible power supply
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
, the connected device can continue operating even when regular office power fails.
Layer 1 hubs versus higher-layer switches
A network hub, or repeater, is a simple network device. Hubs do not manage any of the traffic that comes through them. Any packet entering a portComputer port (hardware)
In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. Physically, a port is a specialized outlet on a piece of equipment to which a plug or cable connects...
is broadcast out or "repeated" on every other port, except for the port of entry. Since every packet is repeated on every other port, packet collisions
Carrier sense multiple access with collision detection
Carrier sense multiple access with collision detection is a Media Access Control method in which:*a carrier sensing scheme is used....
affect the entire network, limiting its capacity.
There are specialized applications where a hub can be useful, such as copying traffic to multiple network sensors. High end switches have a feature which does the same thing called port mirroring
Port mirroring
Port Mirroring is used on a network switch to send a copy of network packets seen on one switch port to a network monitoring connection on another switch port. This is commonly used for network appliances that require monitoring of network traffic, such as an intrusion-detection system...
.
By the early 2000s, there was little price difference between a hub and a low-end switch.
Layer 2
A network bridge, operating at the data link layer, may interconnect a small number of devices in a home or the office. This is a trivial case of bridging, in which the bridge learns the MAC addressMAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
of each connected device.
Single bridges also can provide extremely high performance in specialized applications such as storage area networks.
Classic bridges may also interconnect using a spanning tree protocol
Spanning tree protocol
The Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
that disables links so that the resulting local area network is a tree
Tree (graph theory)
In mathematics, more specifically graph theory, a tree is an undirected graph in which any two vertices are connected by exactly one simple path. In other words, any connected graph without cycles is a tree...
without loops. In contrast to routers, spanning tree bridges must have topologies with only one active path between two points. The older IEEE 802.1D
IEEE 802.1D
802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree and others. It is standardized by the IEEE 802.1 working group. It includes details specific to linking many of the other 802 projects including the widely deployed 802.3 , 802.11 and 802.16 standards.VLANs are not...
spanning tree protocol could be quite slow, with forwarding stopping for 30 seconds while the spanning tree would reconverge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w, but the newest edition of IEEE 802.1D
IEEE 802.1D
802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree and others. It is standardized by the IEEE 802.1 working group. It includes details specific to linking many of the other 802 projects including the widely deployed 802.3 , 802.11 and 802.16 standards.VLANs are not...
adopts the 802.1w extensions as the base standard.
The IETF is specifying the TRILL protocol, which is the application of link-state routing technology to the layer-2 bridging problem. Devices which implement TRILL, called RBridges
Routing Bridge
A Routing Bridge or RBridge is a network device that implements the TRILL protocol, as defined by the IETF, and should not be confused with BRouters . RBridges are compatible with previous IEEE 802.1 customer bridges as well as IPv4 and IPv6 routers and end nodes...
, combine the best features of both routers and bridges.
While "layer 2 switch" remains more of a marketing term than a technical term, the products that were introduced as "switches" tended to use microsegmentation
Microsegmentation
Microsegmentation in computer networking is a term used to describe the segmentation of a collision domain into as many segments as there are circuits, minus one . This microsegmentation performed by the switch cuts the collision domain down so that only two nodes coexist within each collision domain...
and Full duplex to prevent collisions among devices connected to Ethernet. By using an internal forwarding plane
Forwarding plane
In routing, the forwarding plane, sometimes called the data plane, defines the part of the router architecture that decides what to do with packets arriving on an inbound interface...
much faster than any interface, they give the impression of simultaneous paths among multiple devices.
Once a bridge learns the topology through a spanning tree protocol, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth method were performance-increasing methods when used on "switch" products with the same input and output port bandwidths:
- Store and forwardStore and forwardStore and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in a networking context, verifies the integrity of...
: The switch buffers and verifies each frame before forwarding it. - Cut throughCut-through switchingIn computer networking, cut-through switching is a method for packet switching systems, wherein the switch starts forwarding a frame before the whole frame has been received, normally as soon as the destination address is processed...
: The switch reads only up to the frame's hardware address before starting to forward it. Cut-through switches have to fall back to store and forward if the outgoing port is busy at the time the packet arrives. There is no error checking with this method. - Fragment free: A method that attempts to retain the benefits of both store and forward and cut through. Fragment free checks the first 64 byteByteThe byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s of the frameEthernet frameA data packet on an Ethernet link is called an Ethernet frame. A frame begins with Preamble and Start Frame Delimiter. Following which, each Ethernet frame continues with an Ethernet header featuring destination and source MAC addresses. The middle section of the frame is payload data including any...
, where addressingMAC addressA Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device. - Adaptive switchingAdaptive switchingAn adaptive switch is designed to operate in cut-through mode normally but if a port's error rate jumps too high, the switch automatically reconfigures the port to run in store-and-forward mode...
: A method of automatically selecting between the other three modes.
While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is rarely the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth (e.g., 10/100 Mbit/s) into a higher bandwidth (at least 1 Gbit/s). Alternatively, a switch that provides access to server ports usually connects to them at a much higher bandwidth than is used by end user devices.
Layer 3
Within the confines of the Ethernet physical layer, a layer 3 switch can perform some or all of the functions normally performed by a router.The most common layer-3 capability is awareness of IP multicast
IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...
through IGMP snooping
IGMP snooping
IGMP snooping is the process of listening to Internet Group Management Protocol network traffic. IGMP snooping, as implied by the name, is a feature that allows a network switch to listen in on the IGMP conversation between hosts and routers. By listening to these conversations the switch...
. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group.
Layer 4
While the exact meaning of the term Layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translationNetwork address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
, but then adds some type of load distribution
Load balancing (computing)
Load balancing is a computer networking methodology to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid...
based on TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
sessions.
The device may include a stateful firewall
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....
, a VPN concentrator, or be an IPSec
IPsec
Internet Protocol Security is a protocol suite for securing Internet Protocol communications by authenticating and encrypting each IP packet of a communication session...
security gateway.
Layer 7
Layer 7 switches may distribute loads based on URLUniform Resource Locator
In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....
or by some installation-specific technique to recognize application-level transactions. A Layer-7 switch may include a web cache
Web cache
A web cache is a mechanism for the temporary storage of web documents, such as HTML pages and images, to reduce bandwidth usage, server load, and perceived lag...
and participate in a content delivery network
Content Delivery Network
A content delivery network or content distribution network is a system of computers containing copies of data placed at various nodes of a network....
.
Form factor
- Desktop, not mounted in an enclosure, typically intended to be used in a home or office environment outside of a wiring closet
- Rack mounted - A switch that mounts in an equipment rack
- ChassisChassisA chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...
- with swappable module cards - DIN railDIN railA DIN rail is a metal rail of a standard type widely used for mounting circuit breakers and industrial control equipment inside equipment racks...
mounted - normally seen in industrial environments or panels
Configuration options
- Unmanaged switches — These switches have no configuration interface or options. They are plug and play. They are typically the least expensive switches, found in home, SOHO, or small businesses. They can be desktop or rack mounted.
- Managed switches — These switches have one or more methods to modify the operation of the switch. Common management methods include: a command-line interfaceCommand-line interfaceA command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks...
(CLI) accessed via serial console, telnetTELNETTelnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...
or Secure ShellSecure ShellSecure Shell is a network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that it connects via a secure channel over an insecure network: a server and a client...
, an embedded Simple Network Management ProtocolSimple Network Management ProtocolSimple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
(SNMP) agent allowing management from a remote console or management station, or a web interface for management from a web browserWeb browserA web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
. Examples of configuration changes that one can do from a managed switch include: enable features such as Spanning Tree ProtocolSpanning tree protocolThe Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
, set port bandwidth, create or modify Virtual LANVirtual LANA virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location...
s (VLANs), etc. Two sub-classes of managed switches are marketed today:- Smart (or intelligent) switches — These are managed switches with a limited set of management features. Likewise "web-managed" switches are switches which fall in 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 (or fully managed) switches — These 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 larger number of switches and connections, where centralized management is a significant savings in administrative time and effort. A stackable switchStackable switchA 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 switch but having the port capacity of the sum of the...
is a version of enterprise-managed switch.
Traffic monitoring on a switched network
Unless port mirroring or other methods such as RMONRMON
The Remote Network MONitoring MIB was developed by the IETF to support monitoring and protocol analysis of LANs. The original version focused on OSI Layer 1 and Layer 2 information in Ethernet and Token Ring networks...
or SMON are implemented in a switch, it is difficult to monitor traffic that is bridged using a switch because only the sending and receiving ports can see the traffic. These monitoring features are rarely present on consumer-grade switches.
Two popular methods that are specifically designed to allow a network analyst to monitor traffic are:
- Port mirroringPort mirroringPort Mirroring is used on a network switch to send a copy of network packets seen on one switch port to a network monitoring connection on another switch port. This is commonly used for network appliances that require monitoring of network traffic, such as an intrusion-detection system...
— 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.
Another method to monitor may be to connect a Layer-1 hub between the monitored device and its switch port. This will induce minor delay, but will provide multiple interfaces that can be used to monitor the individual switch port.
Typical switch management features
- Turn particular port range on or off
- Link bandwidth and duplexDuplex (telecommunications)A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
settings - Priority settings for ports
- IP Management by IP Clustering.
- MAC filteringMAC filteringIn computer networking, MAC Filtering refers to a security access control method whereby the 48-bit address assigned to each network card is used to determine access to the network....
and other types of "port security" features which prevent MAC floodingMAC floodingIn computer networking, MAC flooding is a technique employed to compromise the security of network switches.Switches maintain a CAM Table that maps individual MAC addresses on the network to the physical ports on the switch... - Use of Spanning Tree ProtocolSpanning tree protocolThe Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
- SNMPSimple Network Management ProtocolSimple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
monitoring of device and link health - Port mirroringPort mirroringPort Mirroring is used on a network switch to send a copy of network packets seen on one switch port to a network monitoring connection on another switch port. This is commonly used for network appliances that require monitoring of network traffic, such as an intrusion-detection system...
(also known as: port monitoring, spanning port, SPAN port, roving analysis port or link mode port) - Link aggregationLink aggregationLink aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
(also known as bonding, trunking or teaming) - VLAN settings
- 802.1X network access controlNetwork Access ControlNetwork Access Control is an approach to computer network security that attempts to unify endpoint security technology , user or system authentication and network security enforcement.-Background:Network Access Control is a computer networking solution that uses a set of protocols to define and...
- IGMP snoopingIGMP snoopingIGMP snooping is the process of listening to Internet Group Management Protocol network traffic. IGMP snooping, as implied by the name, is a feature that allows a network switch to listen in on the IGMP conversation between hosts and routers. By listening to these conversations the switch...
Link aggregation
Link aggregation
Link aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
allows the use of multiple ports for the same connection achieving higher data transfer rates. Creating VLANs can serve security and performance goals by reducing the size of the broadcast domain
Broadcast domain
A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments....
.
See also
- Console serverConsole serverA console server is a device or service that provides access to the system console of a computing device via networking technologies....
- Fully switched network
- LAN switching
- Local area networkLocal area networkA local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
- Multilayer switchMultilayer switchA multilayer switch is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers.- Layer 3 Switching :...
- Network bridge
- Router
- Telephone exchangeTelephone exchangeIn the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
- Turing switchTuring switchThe Turing switch is a logical construction similar to the Turing machine. The Turing switch models the operation of a basic network switch in a network of switches, much the same as a Turing machine models the operation of a basic computational entity. Both are named in honor of the English...
- Wide area networkWide area networkA wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...