LAN switching is a form of packet switching used in local area networks. Switching technologies are crucial to network design, as they allow traffic to be sent only where it is needed in most cases, using fast, hardware-based methods.
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Layer 2 switching is hardware based,[1] which means it uses the media access control address (MAC address) from the host's network interface cards (NICs) to decide where to forward frames. Switches use application-specific integrated circuit (ASICs) to build and maintain filter tables (also known as MAC address tables). One way to think of a layer 2 switch is as a multiport bridge.
Layer 2 switching provides the following
Layer 2 switching is highly efficient because there is no modification to the data packet, only to the frame encapsulation of the packet, and only when the data packet is passing through dissimilar media (such as from Ethernet to FDDI). Layer 2 switching is used for workgroup connectivity and network segmentation (breaking up collision domains). This allows a flatter network design with more network segments than traditional 10BaseT shared networks. Layer 2 switching has helped develop new components in the network infrastructure
These new technologies allow more data to flow off from local subnets and onto a routed network, where a router's performance can become the bottleneck.
Layer 2 switches have the same limitations as bridge networks. Bridges are good if a network is designed by the 80/20 rule: users spend 80 percent of their time on their local segment.
Bridged networks break up collision domains, but the network remains one large broadcast domain. Similarly, layer 2 switches (bridges) cannot break up broadcast domains, which can cause performance issues and limits the size of your network. Broadcast and multicasts, along with the slow convergence of spanning tree, can cause major problems as the network grows. Because of these problems, layer 2 switches cannot completely replace routers in the internetwork.
The only difference between a layer 3 switch and router is the way the administrator creates the physical implementation. Also, traditional routers use microprocessors to make forwarding decisions, and the switch performs only hardware-based packet switching. However, some traditional routers can have other hardware functions as well in some of the higher-end models. Layer 3 switches can be placed anywhere in the network because they handle high-performance LAN traffic and can cost-effectively replace routers. Layer 3 switching is all hardware-based packet forwarding, and all packet forwarding is handled by hardware ASICs. Layer 3 switches really are no different functionally than a traditional router and perform the same functions, which are listed here
The benefits of layer 3 switching include the following
Switching algorithm is relatively simple. it is the same for most of the routing protocols. in most cases a host determines that it must send a packet to another host. Having acquired a routers address by some means, the source host send a packet address specifically to a routers physical(MAC_) address, this time with the protocol(network layer)address of the destination host.
As it examines the packets destinations protocole address, the router determines that it either knows or does not know how to forward packet to the next hop. If the router does not know how to do it, it typically drops the packet. if it knows how to forward packet, however, it changes the destinations physical address to that of the next hop n transmittess the packet.
The next hop may be the destination or the next router, which executes the same switching process. As the packet moves through the internetwork, its physical address changes, but its protocol address remains same.
IEEE has developed the hierarchical terminology that is useful in describing this process. The network devices without capability to forward packets between subnetworks are called end system(ES), whereas network devices with this capabilities are called intermediate systems(IS). IS are further divided into those that can communicate within routing domain(Intradomain ES) and those that communicate both within and between routing domains(Interdomains IS) a routing domain is generally considered as portion of an internetwork under common administrative authority that is regulated by a particular set of administrative guidlines. Routing domains are also called as autonomous systems.
Layer 4 switching is considered a hardware-based layer 3 switching technology that can also consider the application used (for example, Telnet or FTP).
Layer 4 switching provides additional routing above layer 3 by using the port numbers found in the Transport layer header to make routing decisions.
These port numbers are found in Request for Comments (RFC) 1700 and reference the upper-layer protocol, program, or application.
Layer 4 information has been used to help make routing decisions for quite a while. For example, extended access lists can filter packets based on layer 4 port numbers. Another example is accounting information gathered by open standards using sFlow provided by companies like Arista Networks or proprietary solutions like NetFlow switching in Cisco's higher-end routers.
The largest benefit of layer 4 switching is that the network administrator can configure a layer 4 switch to prioritize data traffic by application, which means a QoS can be defined for each user.
For example, a number of users can be defined as a Video group and be assigned more priority, or band-width, based on the need for video conferencing.
Multi-layer switching combines layer 2, 3, and 4 switching technologies and provides high-speed scalability with low latency. It accomplishes this high combination of high-speed scalability with low latency by using huge filter tables based on the criteria designed by the network administrator.
Multi-layer switching can move traffic at wire speed and also provide layer 3 routing, which can remove the bottleneck from the network routers. This technology is based on the idea of "route once, switch many".
Multi-layer switching can make routing/switching decisions based on the following
There is no performance difference between a layer 3 and a layer 4 switch because the routing/switching is all hardware based.