tailieunhanh - Network+ Certification (Outline) - Chapter 3: Network connections

Chapter summary: Bridges selectively relay packets between network segments, depending on their data-link layer destination addresses; bridges maintain a single broadcast domain and create separate collision domains; switches improve on the function of bridges by forwarding packets only to their destination systems; switches reduce the collisions on a network and increase the bandwidth available to each computer;. | Chapter 3 Network Connections 1 Chapter Overview A. Bridging B. Switching C. Routing Chapter 3 Lesson 1 Bridging 2 1. What Is a Bridge A. A data-link layer device that 1. Connects networks 2. Filters packets a. Propagates only packets destined for the other side of the bridge b. Can reduce network traffic and collisions c. Can lessen delays caused by high traffic levels 3 4 2. Connecting LANs with a Bridge A. Usually a hardware device with two ports B. Connects two LANs or splits an existing LAN in half C. Bridges operate in promiscuous mode reading and processing all of the packets transmitted over the network segments. 1. Network interface adapters normally process only the packets that are addressed to them and discard the rest. D. Bridge functions 1. Bridges can read the source and destination addresses in data-link layer protocol headers. a. If the destination address of a packet arriving from one network segment is that of a computer on the other segment the bridge transmits it out through the other port. b. If the destination address is that of a computer on the same network segment as the computer that generated it the bridge discards the packet. 2. The bridge eliminates unnecessary traffic from both segments. 3. Bridges cannot operate any higher than the data-link layer and cannot read any part of the packet other than the data-link layer protocol header. E. Bridges and collisions 1. A collision domain is a network or part of a network that is constructed so that a collision occurs when two computers transmit packets at precisely the same time. 2. Adding a hub to a LAN increases its size but maintains a single collision domain because hubs relay signals immediately at the physical layer without filtering them. 5 6 7 a. Hubs do not relay packets immediately they wait until the entire packet is received. 3. Because the bridge delays propagation computers on opposite sides of the bridge transmitting at the same time do not cause a collision. 4. Adding a .