Top-Down Network Design - Unisinos

1 Top-Down Network DesignChapter FiveDesigning a Network TopologyCopyright 2004 Cisco Press &Priscilla OppenheimerPDF Creator - PDF4 Free A branch of mathematics concerned with thoseproperties of geometric configurations that areunaltered by elastic deformations such asstretching or twisting A termused in the computer networking field todescribe the structure of a networkPDF Creator - PDF4 Free Topology DesignThemes Hierarchy Redundancy Modularity Well-defined entries and exits Protected perimetersPDF Creator - PDF4 Free Use a Hierarchical Model? Reduces workload on Network devices Avoids devices having to communicate withtoo many other devices (reduces CPUadjacencies ) Constrains broadcast domains Enhances simplicity and understanding Facilitates changes Facilitates scaling to a larger sizePDF Creator - PDF4 Free Network DesignEnterprise WANB ackboneCampus ACampus BCampus CBuilding C-1 Building C-2 Campus C BackboneCore LayerDistributionLayerAccess LayerPDF Creator - PDF4 Free s Hierarchical DesignModel A core layer of high-end routers andswitches that are optimized for availabilityand speed A distribution layer of routers and switchesthat implement policies and segment traffic An access layer that connects users viahubs, switches.

2 And other devicesPDF Creator - PDF4 Free Versus HierarchyFlat Loop TopologyHeadquarters inMedfordGrants PassBranch OfficeAshlandBranchOfficeKlamath FallsBranch OfficeHeadquarters inMedfordAshlandBranchOfficeKlamath FallsBranch OfficeGrants PassBranchOfficeWhite CityBranch OfficeHierarchical Redundant TopologyPDF Creator - PDF4 Free TopologyFull-Mesh TopologyPDF Creator - PDF4 Free Partial-Mesh Hierarchical DesignHeadquarters(Core Layer)Branch Offices (Access Layer)RegionalOffices(DistributionLayer) PDF Creator - PDF4 Free Hub-and-Spoke Hierarchical TopologyCorporateHeadquartersBranch OfficeBranch OfficeHome OfficePDF Creator - PDF4 Free Chains and BackdoorsCore LayerDistribution LayerAccess LayerChainBackdoorPDF Creator - PDF4 Free Do You Know When YouHave a Good Design ?

3 When you already know how to add a newbuilding, floor, WAN link, remote site, e-commerce service, and so on When new additions cause only local change, tothe directly-connected devices When your Network can double or triple in sizewithout major Design changes When troubleshooting is easy because there are nocomplex protocol interactions to wrap your brainaroundPDF Creator - PDF4 Free s Enterprise CompositeNetwork ModelNetworkManagementBuildingAccessBuil dingDistributionCampusBackboneServer FarmEdgeDistributionE-CommerceInternetCo nnectivityVPN/ RemoteAccessWANISP AISP BPSTNF rameRelay,ATMC ampusInfrastructureEnterprise CampusEnterprise EdgeServiceProviderEdgePDF Creator - PDF4 Free Topology Design Use a hierarchical, modular approach Minimize the size of bandwidth domains Minimize the size of broadcast domains Provide redundancy Mirrored servers Multiple ways for workstations to reach arouter for off-net communicationsPDF Creator - PDF4 Free Campus Modules Server farm Network management module Edge distribution module for connectivity tothe rest of the world Campus infrastructure module.

4 Building access submodule Building distribution submodule Campus backbonePDF Creator - PDF4 Free Simple Campus Redundant DesignHost AHost BLAN XLAN YSwitch 1 Switch 2 PDF Creator - PDF4 Free and Switches use Spanning-Tree Protocol (STP) to Avoid LoopsXHost AHost BLAN XLAN YSwitch 1 Switch 2 PDF Creator - PDF4 Free (Switches) Running STP Participate with other bridges in the election of a singlebridge as the Root Bridge. Calculate the distance of the shortest path to the RootBridge and choose a port (known as the Root Port) thatprovides the shortest path to the Root Bridge. For each LAN segment, elect a Designated Bridge and aDesignated Port on that bridge. The Designated Port is aport on the LAN segment that is closest to the Root Bridge.

5 (All ports on the Root Bridge are Designated Ports.) Select bridge ports to be included in the spanning tree. Theports selected are the Root Ports and Designated ports forward traffic. Other ports block Creator - PDF4 Free a RootBridge BBridge CBridge A ID = B ID = C ID = 1 Port 2 Port 1 Port 2 Port 1 Port 2 LAN Segment 2100-Mbps EthernetCost = 19 LAN Segment 1100-Mbps EthernetCost = 19 LAN Segment 3100-Mbps EthernetCost = 19 RootBridge ALowest Bridge IDWins!PDF Creator - PDF4 Free Root PortsBridge BBridge CRootBridge ABridge A ID = B ID = C ID = 1 Port 2 Port 1 Port 2 Port 1 Port 2 LAN Segment 2100-Mbps EthernetCost = 19 LAN Segment 1100-Mbps EthernetCost = 19 LAN Segment 3100-Mbps EthernetCost = 19 Root PortRoot PortLowest CostWins!PDF Creator - PDF4 Free Designated PortsBridge BBridge CRootBridge ABridge A ID = B ID = C ID = 1 Port 2 Port 1 Port 2 Port 1 Port 2 LAN Segment 2100-Mbps EthernetCost = 19 LAN Segment 1100-Mbps EthernetCost = 19 LAN Segment 3100-Mbps EthernetCost = 19 Root PortRoot PortDesignated PortDesignated PortDesignated PortLowest Bridge IDWins!

6 PDF Creator - PDF4 Free BBridge CRootBridge ABridge A ID = B ID = C ID = 1 Port 2 Port 1 Port 2 Port 1 Port 2 LAN Segment 2100-Mbps EthernetCost = 19 LAN Segment 1100-Mbps EthernetCost = 19 LAN Segment 3100-Mbps EthernetCost = 19 Root PortRoot PortDesignated PortDesignated PortDesignated PortBlocked PortXPrune Topology into a Tree!PDF Creator - PDF4 Free to ChangesBridge BBridge CRootBridge ABridge A ID = B ID = C ID = 1 Port 2 Port 1 Port 2 Port 1 Port 2 LAN Segment 2 LAN Segment 1 LAN Segment 3 Root PortRoot PortDesignated PortDesignated PortDesignated Port BecomesDisabledBlocked Port Transitions toForwarding StatePDF Creator - PDF4 Free the Spanning TreeProtocol Keep the switched Network small It shouldn t span more than seven switches Use BPDU skew detection on Ciscoswitches Use IEEE Provides rapid reconfiguration of the spanningtree Also known as RSTPPDF Creator - PDF4 Free LANs (VLANs)

7 An emulation of a standard LAN that allowsdata transfer to take place without thetraditional physical restraints placed on anetwork A set of devices that belong to anadministrative group Designers use VLANs to constrainbroadcast trafficPDF Creator - PDF4 Free versus Real LANsSwitch AStation A1 Station A2 Station A3 Network ASwitch BStation B1 Station B2 Station B3 Network BPDF Creator - PDF4 Free Switch with VLANsStation A1 Station A2 Station A3 VLAN AStation B1 Station B2 Station B3 VLAN BPDF Creator - PDF4 Free Span SwitchesSwitch AStation B1 Station B2 Station B3 Switch BStation B4 Station B5 Station B6 Station A1 Station A2 Station A3 Station A4 Station A5 Station A6 VLAN BVLAN AVLAN BVLAN APDF Creator - PDF4 Free and VLANs A wireless LAN (WLAN) is oftenimplemented as a VLAN Facilitates roaming Users remain in the same VLAN and IPsubnet as they roam, so there s no need tochange addressing information Also makes it easier to set up filters (accesscontrol lists) to protect the wired networkfromwireless usersPDF Creator - PDF4 Free Proxy ARP (not a good idea) Listen for route advertisements (not a greatidea either) ICMP router solicitations (not widely used) Default gateway provided by DHCP (betteridea but no redundancy) Use Hot Standby Router Protocol (HSRP)

8 ForredundancyPDF Creator - PDF4 Free RouterStandby RouterVirtual RouterWorkstationEnterprise InternetworkPDF Creator - PDF4 Free the InternetConnectionEnterpriseEnterpriseEn terpriseISP 1 ISP 1 ISP 2 ISP 1 ISP 1 ISP 2 EnterpriseOption AOption BOption COption DParisNYParisNYPDF Creator - PDF4 Free TopologiesEnterpriseNetworkDMZWeb, File, DNS, Mail ServersInternetPDF Creator - PDF4 Free TopologiesInternetEnterprise NetworkDMZWeb, File, DNS, Mail ServersFirewallPDF Creator - PDF4 Free Use a systematic, Top-Down approach Plan the logical Design before the physicaldesign Topology Design should feature hierarchy,redundancy, modularity, and securityPDF Creator - PDF4 Free Questions Why are hierarchy and modularity important fornetwork designs?

9 What are the three layers of Cisco s hierarchicalnetwork Design ? What are the major components of Cisco s enterprisecomposite Network model? What are the advantages and disadvantages of thevarious options for multihoming an Internetconnection?PDF Creator - PDF4 Free