Switche and Bridge Function at Data Link Layer | Features

The Layer 2 Switching can be regarded as hardware based bridging as it employs a particular hardware, which is called an Application Specific Integrated Circuit (ASIC). Application Specific Integrated Circuits (ASIC) works on gigabit rate with very low latency rates. Latency is a calculated time when a frame enters in a port and exits a port.

Layer 2 devices (Bridges and switches) read each frame on the network. Then insert the source MAC address in a filter table and stay tracking the port on which the frame was arrived. Switches and Bridges create logs in the filter table for this information. Routers always find the particular network while switches and bridges always find the particular device. The routing table exists in a router to “map” the internetwork while filter tables exists in the switches and network to “map” the individual devices. Filter table only sends frames to the segment where the destination MAC address is situated. If the destined host is on the same segment like the frame, switch or bridge will prevents the frame to going to any other segments. But if the destination is on another segment, the frame will be transmitted only to that segment. This whole method is called transparent bridging. When an interface of layer 2 device gets a frame with destination MAC address which is not listed in the filter table, it will send that frame to all connected segments. After it, when an unknown host which was sent that frame responds to this sending deed, the layer 2 device (sending device) will update its filter table concerning that host’s position. In this process, the destination address of the transmitting frame is a broadcast address and switch or bridge (layer 2 devices) by default forward all broadcasts to each connected segment.

Switch in an Internetwork

The major advantage of using switches is that every switch port is a separate collision domain. But the broadcast domain is the same on all ports of the switch or bridge. So they always normally forward all broadcasts instead. The other advantage of the switched LAN above the hubs LAN is that every host on each segment of the switch can transmit at the same time, while the hub never offers this kind of efficient service, because they permit transmission only to one host per network segment at a time.

This article is relate to the comparison to the layer 2 devices, such as Switches and Bridges advantages over the Hubs according to the CCNA 640-802 Cisco Certified Network Associate’ course detail 2011.

Posted by Fahad Bin Ali KhilGi - You can follow any responses to this entry through the RSS 2.0. You can also leave a response or trackback to this entry. - Thank You - | - ALLAH HAFIZ