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ccna 200 301 bookstore chains out of business.Logical Link Control (LLC) 802.2 is responsible for identifying network layer protocols and then encapsulating them. The LLC header is responsible for telling the data link layer what to do with this data frame once it is received. Here's how it works: after a host receives a data frame, it looks at the LLC header in order to know where the packet is going-that is, the IP protocols located at the network layer. The LLC can also provide flow control and sort the control bits.The switches and bridges I mentioned at the beginning of this chapter both work at the data link layer and filter network information based on hardware (MAC) addresses. We discuss this part in more detail next.Switches and bridges that work at the data link layerWe think of Layer 2 switching as hardware-based bridging because it uses a specialized piece of hardware called an ASIC (Application Specific Integrated Circuit). ASICs can work at gigabit rates and have very low latency.Latency in this context refers to the time it takes from the time a data frame enters a port, to the time it leaves the entire port.The bridge and switch will read the contents of the data frame as it traverses the network. Layer 2 devices will put the source hardware address into a filter table in order to record the port from which this data frame was received. This information (recorded in the bridge and switch filter tables) helps the device determine the location of specific end devices. Figure 2.16 illustrates the interSwitches in the United Network.The key to the premises industry is location, location, location, and the same is true for Layer 2 and Layer 3 devices. While both types of devices need the ability to sense the network topology, they have different concerns. Essentially, Layer 3 devices (such as routers) need to locate specific networks, while Layer 2 devices (such as switches and bridges) need to locate specific devices. Thus routers are concerned with the network, and switches and bridges are concerned with each deviceEach network segment is a conflict domain. All network segments belong to the same broadcast domain. Figure 2.16 Switches in an interconnected networkBackup. The routing table in the router "maps" the interconnected network, while the filtering table in the switch and bridge "maps" each device.