Connecting LANS Backbone Networks and Virtual Lans

15.1Chapter 15Connecting LANs, Backbone Networks, and Virtual LANsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.15.215-1 CONNECTING DEVICESInthissection,wedivideconnectingdevicesintofivedifferentcategoriesbasedonthelayerinwhichtheyoperateinanetwork.Passive HubsActive HubsBridgesTwo-Layer SwitchesRoutersThree-Layer SwitchesGatewaysTopics discussed in this section:15.3Figure 15.1 Five categories of connecting devices15.4Figure 15.2 A repeater connecting two segments of a LAN15.5A repeater connects segments of a LAN.Note15.6A repeater forwards every frame; it has no filtering capability.Note15.7A repeater is a regenerator, not an amplifier.Note15.8Figure 15.3 Function of a repeater15.9Figure 15.4 A hierarchy of hubs15.10A bridge has a table used in filtering decisions.Note15.11Figure 15.5 A bridge connecting two LANs15.12A bridge does not change the physical (MAC) addresses in a frame.Note15.13Figure 15.6 A learning bridge and the process of learning15.14Figure 15.7 Loop problem in a learning bridge15.15Figure 15.8 A system of connected LANs and its graph representation15.16Figure 15.9 Finding the shortest paths and the spanning tree in a system of bridges15.17Figure 15.10 Forwarding and blocking ports after using spanning tree algorithm15.18Figure 15.11 Routers connecting independent LANs and WANs15.1915-2 BACKBONE NETWORKSAbackbonenetworkallowsseveralLANstobeconnected.Inabackbonenetwork,nostationisdirectlyconnectedtothebackbone;thestationsarepartofaLAN,andthebackboneconnectstheLANs.Bus BackboneStar BackboneConnecting Remote LANsTopics discussed in this section:15.20In a bus backbone, the topology of the backbone is a bus.Note15.21Figure 15.12 Bus backbone15.22In a star backbone, the topology of the backbone is a star;the backbone is just one switch.Note15.23Figure 15.13 Star backbone15.24Figure 15.14 Connecting remote LANs with bridges15.25A point-to-point link acts as a LAN in a remote backbone connected by remote bridges.Note15.2615-3 VIRTUAL LANsWecanroughlydefineavirtuallocalareanetwork(VLAN)asalocalareanetworkconfiguredbysoftware,notbyphysicalwiring.MembershipConfigurationCommunication between SwitchesIEEE StandardAdvantagesTopics discussed in this section:15.27Figure 15.15 A switch connecting three LANs15.28Figure 15.16 A switch using VLAN software15.29Figure 15.17 Two switches in a backbone using VLAN software15.30VLANs create broadcast domains.Note