Pokrewne
- Strona Główna
- Radiation Protection A Guide for Scientists, Regulators and Physicians Jacob Shapiro
- 802.11 Wireless Networks The Definitive Guide Oreilly Excellent
- The Career Survival Guide Dealing with Office Politics Brian OConnell
- CorelDRAW 11 and Corel RAVE 2 User Guide
- (ebook computers) Visual C .NET Developers Guide
- Novell Netware 5 Advanced Admin Instructor guide
- Corel PHOTO PAINT 11 User Guide
- Violet Blue The Ultimate Guide to Cunilingus
- Duncan Dave Dar Madrosci
- Margit Sandemo Saga o Ludziach Lodu t.4
- zanotowane.pl
- doc.pisz.pl
- pdf.pisz.pl
- anndan.keep.pl
[ Pobierz całość w formacie PDF ]
.Hierarchical design facilitates changes.In a network design, modularity allows creating designelements that can be replicated as the network grows, facilitating easy network growth.As eachelement in the network design requires change, the cost and complexity of making the upgradeis contained to a small subset of the overall network.In large, flat, or meshed networkarchitectures, changes tend to impact a large number of systems.Improved fault isolation is facilitated by structuring the network into small, easy-to-understandelements.Network managers can easily understand the transition points in the network, whichhelps identify failure points.Today s fast-converging protocols were designed for hierarchical topologies.To control theimpact of routing overhead processing and bandwidth consumption, modular hierarchicaltopologies must be used with protocols designed with these controls in mind, such as EIGRP.Route summarization is facilitated by hierarchical network design.Route summarizationreduces the routing protocol overhead on links in the network and reduces routing protocolprocessing within the routers. CH01.book Page 104 Friday, January 7, 2000 5:35 PM104 Chapter 4: Network Topologies and LAN DesignHierarchical Network DesignAs Figure 4-1 illustrates, a hierarchical network design has three layers:" The core layer provides optimal transport between sites." The distribution layer provides policy-based connectivity." The access layer provides workgroup/user access to the network.Figure 4-1 A Hierarchical Network Design Has Three Layers: Core, Distribution, and AccessCoreDistributionHigh-Speed SwitchingAccessPolicy-Based ConnectivityLocal and Remote Workgroup AccessEach layer provides necessary functionality to the network.The layers do not need to beimplemented as distinct physical entities.Each layer can be implemented in routers or switches,represented by a physical media, or combined in a single box.A particular layer can be omittedaltogether, but for optimum performance, a hierarchy should be maintained.Core LayerThe core layer is the high-speed switching backbone of the network, which is crucial to enablecorporate communications.The core layer should have the following characteristics:" Offer high reliability" Provide redundancy" Provide fault tolerance" Adapt to changes quickly" Offer low latency and good manageability" Avoid slow packet manipulation caused by filters or other processes" Have a limited and consistent diameter CH01.book Page 105 Friday, January 7, 2000 5:35 PMLAN Topology Design 105NOTE When routers are used in a network, the number of router hops from edge to edge is called thediameter.As noted, it is considered good practice to design for a consistent diameter within ahierarchical network.This means that from any end station to another end station across thebackbone, there should be the same number of hops.The distance from any end station to aserver on the backbone should also be consistent.Limiting the diameter of the internetwork provides predictable performance and ease oftroubleshooting.Distribution layer routers and client LANs can be added to the hierarchicalmodel without increasing the diameter because neither will affect how existing end stationscommunicate.Distribution LayerThe distribution layer of the network is the demarcation point between the access and corelayers of the network.The distribution layer can have many roles, including implementing thefollowing functions:" Policy (for example, to ensure that traffic sent from a particular network should beforwarded out one interface, while all other traffic should be forwarded out anotherinterface)" Security" Address or area aggregation or summarization" Departmental or workgroup access" Broadcast/multicast domain definition" Routing between virtual LANs (VLANs)" Media translations (for example, between Ethernet and Token Ring)" Redistribution between routing domains (for example, between two different routingprotocols)" Demarcation between static and dynamic routing protocolsSeveral Cisco IOS software features can be used to implement policy at the distribution layer,including the following:" Filtering by source or destination address" Filtering on input or output ports" Hiding internal network numbers by route filtering" Static routing CH01.book Page 106 Friday, January 7, 2000 5:35 PM106 Chapter 4: Network Topologies and LAN Design" Quality of service mechanisms (for example, to ensure that all devices along a path canaccommodate the requested parameters)Access LayerThe access layer provides user access to local segments on the network.The access layer ischaracterized by switched and shared bandwidth LANs in a campus environment.Microsegmentation, using LAN switches, provides high bandwidth to workgroups by dividingcollision domains on Ethernet segments and reducing the number of stations capturing thetoken on Token Ring LANs.For small office/home office (SOHO) environments, the access layer provides access for remotesites into the corporate network by using WAN technologies such as ISDN, Frame Relay, andleased lines.Features such as dial-on-demand routing (DDR) and static routing can beimplemented to control costs.Hierarchical Model ExamplesFor small- to medium-sized companies, the hierarchical model is often implemented as a hub-and-spoke topology, as shown in Figure 4-2.Corporate headquarters forms the hub and links tothe remote offices form the spokes.Figure 4-2 The Hierarchical Model Is Often Implemented as a Hub-and-Spoke TopologyCorporateHeadquartersRemoteOfficesHome Office CH01.book Page 107 Friday, January 7, 2000 5:35 PMLAN Topology Design 107You can implement the hierarchical model by using either routers or switches [ Pobierz całość w formacie PDF ]
zanotowane.pl doc.pisz.pl pdf.pisz.pl agnieszka90.opx.pl
.Hierarchical design facilitates changes.In a network design, modularity allows creating designelements that can be replicated as the network grows, facilitating easy network growth.As eachelement in the network design requires change, the cost and complexity of making the upgradeis contained to a small subset of the overall network.In large, flat, or meshed networkarchitectures, changes tend to impact a large number of systems.Improved fault isolation is facilitated by structuring the network into small, easy-to-understandelements.Network managers can easily understand the transition points in the network, whichhelps identify failure points.Today s fast-converging protocols were designed for hierarchical topologies.To control theimpact of routing overhead processing and bandwidth consumption, modular hierarchicaltopologies must be used with protocols designed with these controls in mind, such as EIGRP.Route summarization is facilitated by hierarchical network design.Route summarizationreduces the routing protocol overhead on links in the network and reduces routing protocolprocessing within the routers. CH01.book Page 104 Friday, January 7, 2000 5:35 PM104 Chapter 4: Network Topologies and LAN DesignHierarchical Network DesignAs Figure 4-1 illustrates, a hierarchical network design has three layers:" The core layer provides optimal transport between sites." The distribution layer provides policy-based connectivity." The access layer provides workgroup/user access to the network.Figure 4-1 A Hierarchical Network Design Has Three Layers: Core, Distribution, and AccessCoreDistributionHigh-Speed SwitchingAccessPolicy-Based ConnectivityLocal and Remote Workgroup AccessEach layer provides necessary functionality to the network.The layers do not need to beimplemented as distinct physical entities.Each layer can be implemented in routers or switches,represented by a physical media, or combined in a single box.A particular layer can be omittedaltogether, but for optimum performance, a hierarchy should be maintained.Core LayerThe core layer is the high-speed switching backbone of the network, which is crucial to enablecorporate communications.The core layer should have the following characteristics:" Offer high reliability" Provide redundancy" Provide fault tolerance" Adapt to changes quickly" Offer low latency and good manageability" Avoid slow packet manipulation caused by filters or other processes" Have a limited and consistent diameter CH01.book Page 105 Friday, January 7, 2000 5:35 PMLAN Topology Design 105NOTE When routers are used in a network, the number of router hops from edge to edge is called thediameter.As noted, it is considered good practice to design for a consistent diameter within ahierarchical network.This means that from any end station to another end station across thebackbone, there should be the same number of hops.The distance from any end station to aserver on the backbone should also be consistent.Limiting the diameter of the internetwork provides predictable performance and ease oftroubleshooting.Distribution layer routers and client LANs can be added to the hierarchicalmodel without increasing the diameter because neither will affect how existing end stationscommunicate.Distribution LayerThe distribution layer of the network is the demarcation point between the access and corelayers of the network.The distribution layer can have many roles, including implementing thefollowing functions:" Policy (for example, to ensure that traffic sent from a particular network should beforwarded out one interface, while all other traffic should be forwarded out anotherinterface)" Security" Address or area aggregation or summarization" Departmental or workgroup access" Broadcast/multicast domain definition" Routing between virtual LANs (VLANs)" Media translations (for example, between Ethernet and Token Ring)" Redistribution between routing domains (for example, between two different routingprotocols)" Demarcation between static and dynamic routing protocolsSeveral Cisco IOS software features can be used to implement policy at the distribution layer,including the following:" Filtering by source or destination address" Filtering on input or output ports" Hiding internal network numbers by route filtering" Static routing CH01.book Page 106 Friday, January 7, 2000 5:35 PM106 Chapter 4: Network Topologies and LAN Design" Quality of service mechanisms (for example, to ensure that all devices along a path canaccommodate the requested parameters)Access LayerThe access layer provides user access to local segments on the network.The access layer ischaracterized by switched and shared bandwidth LANs in a campus environment.Microsegmentation, using LAN switches, provides high bandwidth to workgroups by dividingcollision domains on Ethernet segments and reducing the number of stations capturing thetoken on Token Ring LANs.For small office/home office (SOHO) environments, the access layer provides access for remotesites into the corporate network by using WAN technologies such as ISDN, Frame Relay, andleased lines.Features such as dial-on-demand routing (DDR) and static routing can beimplemented to control costs.Hierarchical Model ExamplesFor small- to medium-sized companies, the hierarchical model is often implemented as a hub-and-spoke topology, as shown in Figure 4-2.Corporate headquarters forms the hub and links tothe remote offices form the spokes.Figure 4-2 The Hierarchical Model Is Often Implemented as a Hub-and-Spoke TopologyCorporateHeadquartersRemoteOfficesHome Office CH01.book Page 107 Friday, January 7, 2000 5:35 PMLAN Topology Design 107You can implement the hierarchical model by using either routers or switches [ Pobierz całość w formacie PDF ]