Bài giảng Network - Chapter 10

Chapter Overview BridgingSwitchingRouting 1What Is a Bridge? A data-link layer device that connects networks and filters packets Propagates only packets destined for the other side of the bridgeCan reduce network traffic and collisionsCan lessen delays 2Connecting LANs with a Bridge 3Bridges and Collisions 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.Adding a hub to a local area network (LAN) increases its size but maintains a single collision domain because hubs relay signals immediately at the physical layer, without filtering them.Hubs do not relay packets immediately; they wait until the entire packet is received. Because the bridge delays propagation, computers on opposite sides of the bridge transmitting at the same time do not cause a collision.Adding a bridge to a LAN splits it into two collision domains, resulting in fewer collisions and increased efficiency. 4Broadcasts 5Bridges and Broadcasts Bridges propagate all broadcast packets without filtering them.The network segments on either side of a bridge are in the same broadcast domain. 6Transparent Bridging Transparent bridging is a method for automatically compiling a bridge’s address tables.Bridges maintain an address table for each network segment.Bridges read the source and destination addresses of packets and compare them to the tables to determine whether to propagate them.When a bridge lacks the information needed to filter a packet, it propagates the packet by default. 7Bridge Types Local bridge. Connects network segments of the same type and at the same locationTranslation bridge. Connects network segments at the same location that use different media or different protocolsRemote bridge. Connects network segments at remote locations, using a wide area network (WAN) link 8Translation Bridge 9Switch Characteristics Data-link layer deviceReplaces bridges and sometimes routersSimilar in appearance to a hubForwards incoming traffic out to the destination port onlyConverts a shared network medium to a dedicated oneOffers advantages such as reduced network congestion and the use of full network bandwidthCan operate in full-duplex mode 10Switching 11Replacing Routers with Switches 12Virtual LANs A virtual LAN (VLAN) is a subnet that exists inside a switch.Broadcasts sent by a computer go only to the other computers in the VLAN.Communications within a VLAN are switched.Communications between VLANs can be routed or switched. 13Layer 3 Switching Layer 3 switching minimizes the amount of routing between VLANs because routing occurs only when absolutely necessary.A router establishes a connection between systems and then switches take over. 14Switch Types A cut-through switch begins to forward packets immediately.A store-and-forward switch waits until the entire packet arrives before forwarding it. 15Router Characteristics Connect networks together to form an internetworkAre network layer devicesCan connect LANs running different data-link layer protocols 16Router Functions Forward packets to the destination networkStrip the data-link layer frames from incoming packets and repackage the data into new framesFragment packets when necessary 17Routing Process Example 18Hops 19Routing Tables Routing tables are essential to the router operation and functions.There are two methods of creating routing tables: Static routing. Manual creation of routing table entries by an administratorDynamic routing. Automatic creation of routing table entries by using a specialized routing protocol 20Router Types Routers can be stand-alone hardware devices or software running on a computer. Hardware routers. Range from expensive rack-mounted devices to small stand-alone unitsSoftware routers. Include Microsoft Windows 2000 Internet Connection Sharing (ICS), and Routing and Remote Access 21Chapter Summary BridgingBridges 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. Switching 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. Routing Routers are used to connect networks together at the network layer of the OSI reference model. Routers strip away the data-link layer frame of incoming packets and build a new frame using the data-link layer protocol of the outgoing network. Routing tables can be created manually by a network administrator or automatically by a routing protocol. 22