Bài giảng Network Certification Microsoft Press - Chapter 10

1Chapter Overview  Bridging  Switching  Routing 2What Is a Bridge?  A data-link layer device that connects networks and filters packets  Propagates only packets destined for the other side of the bridge  Can reduce network traffic and collisions  Can lessen delays 3Connecting LANs with a Bridge 4Bridges 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. 5Broadcasts 6Bridges 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. 7Transparent 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. 8Bridge Types  Local bridge. Connects network segments of the same type and at the same location  Translation bridge. Connects network segments at the same location that use different media or different protocols  Remote bridge. Connects network segments at remote locations, using a wide area network (WAN) link 9Translation Bridge 10 Switch Characteristics  Data-link layer device  Replaces bridges and sometimes routers  Similar in appearance to a hub  Forwards incoming traffic out to the destination port only  Converts a shared network medium to a dedicated one  Offers advantages such as reduced network congestion and the use of full network bandwidth  Can operate in full-duplex mode 11 Switching 12 Replacing Routers with Switches 13 Virtual 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. 14 Layer 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. 15 Switch Types  A cut-through switch begins to forward packets immediately.  A store-and-forward switch waits until the entire packet arrives before forwarding it. 16 Router Characteristics  Connect networks together to form an internetwork  Are network layer devices  Can connect LANs running different data-link layer protocols 17 Router Functions  Forward packets to the destination network  Strip the data-link layer frames from incoming packets and repackage the data into new frames  Fragment packets when necessary 18 Routing Process Example 19 Hops 20 Routing 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 administrator  Dynamic routing. Automatic creation of routing table entries by using a specialized routing protocol 21 Router 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 units  Software routers. Include Microsoft Windows 2000 Internet Connection Sharing (ICS), and Routing and Remote Access 22 Chapter Summary  Bridging  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.  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.