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Ethernet switch latency / Layer 2 and Layer 3 switching

Ethernet switch latency
 4.2.6 Switch latency is the period of time when a frame enters a switch to the time it takes the frame to exit the switch. Latency is directly related to the configured switching process and volume of traffic. 
Latency is measured in fractions of a second. Network devices operate at incredibly high speeds so every additional nanosecond of latency adversely affects network performance.
The next page will describe Layer 2 and Layer 3 switching.
Layer 2 and Layer 3 switching 
4.2.7 There are two methods of switching data frames, Layer 2 switching and Layer 3 switching. Routers and Layer 3 switches use Layer 3 switching to switch packets. Layer 2 switches and bridges use Layer 2 switching to forward frames.
The difference between Layer 2 and Layer 3 switching is the type of information inside the frame that is used to determine the correct output interface. Layer 2 switching is based on MAC address information. Layer 3 switching is based on network layer addresses, or IP addresses. The features and functionality of Layer 3 switches and routers have numerous similarities. The only major difference between the packet switching operation of a router and a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place in software, using microprocessor-based engines, whereas a Layer 3 switch performs packet forwarding using application specific integrated circuit (ASIC) hardware.
Layer 2 switching looks at a destination MAC address in the frame header and forwards the frame to the appropriate interface or port based on the MAC address in the switching table. The switching table is contained in Content Addressable Memory (CAM). If the Layer 2 switch does not know where to send the frame, it broadcasts the frame out all ports to the network. When a reply is returned, the switch records the new address in the CAM.
Layer 3 switching is a function of the network layer. The Layer 3 header information is examined and the packet is forwarded based on the IP address.
Traffic flow in a switched or flat network is inherently different from the traffic flow in a routed or hierarchical network. Hierarchical networks offer more flexible traffic flow than flat networks.
The next page will discuss symmetric and asymmetric switching.

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