Multilayer switch
Encyclopedia
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
.
switch is the physical implementation. In general-purpose routers, packet switching takes place using software which runs on a microprocessor, whereas a Layer 3 switch performs this using dedicated application-specific integrated circuit
(ASIC) hardware.
DSCP (differentiated services
CodePoint). These 8 bits were used in the "old days" for Type of Service
(ToS
).
The following 4 mappings are normally available in an MLS:
Many MLSs implement QoS
differentiated services
and/or integrated services
in hardware.
Some MLS's are also able to route between VLANs and/or port
s like a common router. The routing is normally as quick as switching (at wirespeed). According to Cisco
, Layer 3 switches are basically routers that switch based on Layer 3 information, the basic difference being processing speed and/or the way they do the switching; Layer 3 switches use ASIC
s/hardware
instead of the CPU
/software that a router would.
Content switches are typically used for load balancing among groups of servers. Load balancing can be performed on HTTP, HTTPS
, VPN, or any TCP/IP traffic using a specific port. Load balancing often involves NAT
so that the client of the load balanced service is not fully aware of precisely which server is handling its requests. Some of the layer 4-7 switches can perform NAT
at wirespeed. Also, content switches can often be used to perform standard operations such as SSL encryption/decryption to reduce the load on the servers receiving the traffic, or to centralise the management of digital certificates. Layer 7 switching is the base technology of a content delivery network
.
Some types of applications require that repeated requests from a client are directed at the same application server. Since the client isn't generally aware of which server it spoke to earlier, content switches define a notion of stickiness. For example, requests from the same source IP address are directed to the same application server each time. Stickiness can also be based on SSL IDs, and some content switches can even use cookies
to provide this functionality.
on its network. A layer 4
router, more correctly a NAT with port and transaction awareness, uses a little trickery and sends incoming packets to one or more machines which are hidden behind a single IP address.
The layer 4
refers to the 7 layer OSI model
. The router is on the Transport Layer
and makes decisions on where to send the packets. Modern load balancing
routers can use different rules to make decisions on where to route traffic. This can be based on least load, or fastest response times, or simply balancing requests out. This is also a redundancy
method, so if one machine is not up, the router will not send traffic to it.
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 switches on OSI layer 2
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....
like an ordinary network switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
and provides extra functions on higher OSI layers
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...
.
Layer 3 Switching
The major difference between the packet switching operation of a router and that of a Layer 3Network 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...
switch is the physical implementation. In general-purpose routers, packet switching takes place using software which runs on a microprocessor, whereas a Layer 3 switch performs this using dedicated application-specific integrated circuit
Application-specific integrated circuit
An application-specific integrated circuit is an integrated circuit customized for a particular use, rather than intended for general-purpose use. For example, a chip designed solely to run a cell phone is an ASIC...
(ASIC) hardware.
MultiLayer Switch (MLS) - OSI layer 3 and/or 4
A Multilayer Switch (MLS) can prioritize packets by the 8 bits in IPInternet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
DSCP (differentiated services
Differentiated services
Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...
CodePoint). These 8 bits were used in the "old days" for Type of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(ToS
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
).
The following 4 mappings are normally available in an MLS:
- From OSI layer 2, 3 or 4OSI modelThe 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 IP DSCP (if IP packet) and/or VLAN IEEE 802.1pQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
. - From VLAN IEEE 802.1pQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
to IP DSCP. - From IP DSCP to VLAN IEEE 802.1pQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
. - From VLAN IEEE 802.1pQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
to port queueComputer port (software)In computer programming, port has a wide range of meanings.A software port is a virtual/logical data connection that can be used by programs to exchange data directly, instead of going through a file or other temporary storage location...
.
Many MLSs implement QoS
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
differentiated services
Differentiated services
Differentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...
and/or integrated services
Integrated services
In computer networking, IntServ or integrated services is an architecture that specifies the elements to guarantee quality of service on networks...
in hardware.
Some MLS's are also able to route between VLANs and/or port
Computer port (software)
In computer programming, port has a wide range of meanings.A software port is a virtual/logical data connection that can be used by programs to exchange data directly, instead of going through a file or other temporary storage location...
s like a common router. The routing is normally as quick as switching (at wirespeed). According to Cisco
Cisco Systems
Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...
, Layer 3 switches are basically routers that switch based on Layer 3 information, the basic difference being processing speed and/or the way they do the switching; Layer 3 switches use ASIC
ASIC
ASIC may refer to:* Application-specific integrated circuit, an integrated circuit developed for a particular use, as opposed to a customised general-purpose device.* ASIC programming language, a dialect of BASIC...
s/hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
instead of the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
/software that a router would.
Layer 4-7 switch, web-switch, content-switch
Some switches can use up to OSI layer 7 packet information; these may be called layer 4-7 switches, content-switches, content services switches, web-switches or application-switches.Content switches are typically used for load balancing among groups of servers. Load balancing can be performed on HTTP, HTTPS
Https
Hypertext Transfer Protocol Secure is a combination of the Hypertext Transfer Protocol with SSL/TLS protocol to provide encrypted communication and secure identification of a network web server...
, VPN, or any TCP/IP traffic using a specific port. Load balancing often involves NAT
Network 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....
so that the client of the load balanced service is not fully aware of precisely which server is handling its requests. Some of the layer 4-7 switches can perform NAT
Network 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....
at wirespeed. Also, content switches can often be used to perform standard operations such as SSL encryption/decryption to reduce the load on the servers receiving the traffic, or to centralise the management of digital certificates. Layer 7 switching is the base technology of 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....
.
Some types of applications require that repeated requests from a client are directed at the same application server. Since the client isn't generally aware of which server it spoke to earlier, content switches define a notion of stickiness. For example, requests from the same source IP address are directed to the same application server each time. Stickiness can also be based on SSL IDs, and some content switches can even use cookies
HTTP cookie
A cookie, also known as an HTTP cookie, web cookie, or browser cookie, is used for an origin website to send state information to a user's browser and for the browser to return the state information to the origin site...
to provide this functionality.
Layer 4 Load Balancer
A typical network router simply sends incoming packets onto the appropriate IP addressIP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
on its network. A layer 4
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
router, more correctly a NAT with port and transaction awareness, uses a little trickery and sends incoming packets to one or more machines which are hidden behind a single IP address.
The layer 4
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
refers to the 7 layer 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...
. The router is on the Transport Layer
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
and makes decisions on where to send the packets. Modern load balancing
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...
routers can use different rules to make decisions on where to route traffic. This can be based on least load, or fastest response times, or simply balancing requests out. This is also a redundancy
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
method, so if one machine is not up, the router will not send traffic to it.
See also
- Multiprotocol Label Switching (MPLS)Multiprotocol Label SwitchingMultiprotocol Label Switching is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. The labels identify virtual links between...
- LAN switching
- Network switchNetwork switchA network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
- Application delivery controllerApplication delivery controllerAn application delivery controller is a network device in the datacenter that helps perform common tasks done by web sites in an effort to remove load from the web servers themselves. Many also provide load balancing. They usually sit between the firewall/router and the web farm. The ADC is in...
- Residential gatewayResidential gatewayA 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...