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Network Structure Models

Network Structure Models. Chapter Topics. Hierarchical Network Models Enterprise Composite Network Model Network Availability. Foundation. Cisco has two different models to help simplify the design process Hierarchical Model Enterprise Composite Network Model. Hierarchical Network Model.

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Network Structure Models

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  1. Network Structure Models

  2. Chapter Topics • Hierarchical Network Models • Enterprise Composite Network Model • Network Availability

  3. Foundation • Cisco has two different models to help simplify the design process • Hierarchical Model • Enterprise Composite Network Model

  4. Hierarchical Network Model • Enables you to design internetworks that use specialization of function combined with an hierarchical organization • Simplifies tasks required to build a network • Uses layers to simplify tasks • Each layer focuses on specific tasks • Can apply to both LAN & WAN designs

  5. Benefits of the Hierarchical Model • Cost Savings • Modular design means no longer doing everything on one platform • Conserve bandwidth within each layer • Ease of Understanding • Easy model means easy design • Leads to ease of understanding • NM Software can be distributed easier, meaning easier to control the network • Helps to keep costs down as well

  6. Benefits of the Hierarchical Model • Modular Network Growth • If your network grows, change or upgrade the layer that needs it, not the entire network • Improved Fault Isolation • Managers knows where transition points are, thereby identifying failures more quickly

  7. Benefits of the Hierarchical Model • Fast converging Protocols were designed for hierarchical topologies • OSPF can be used to it’s potential • Hierarchical Design facilitates route summarization • Summarize a lower layer into a higher layer • Reduced routing overhead on the links • Reduced routing-protocol processing on the routers

  8. Hierarchical Network Design • Three Layers to a traditional hierarchical design • Core • Distribution • Access • Each layer provides necessary functionality to the enterprise network • Layers do not need to be separate physical devices • Smaller networks could collapse multiple layers to a single device

  9. The Hierarchical Design Model

  10. Core Layer • The high-speed switching backbone of the network • Crucial to corporate communications • Plan to have a consistent diameter • # of router hops from edge to edge • Distance from any End Station to a server should be consistent • Limiting diameter size also provides better predictability and ease of troubleshooting

  11. Characteristics of the Core Layer • Fast transport • High reliability • Redundancy • Fault tolerance

  12. Characteristics of the Core Layer • Quick adaptation (adapt to changes quickly) • Low latency and good manageability • Avoidance of slow packet manipulation caused by filters or other processes • Limited and consistent diameter

  13. Distribution Layer • The isolation point between the access and core layers of the network. • provides aggregation of routes providing route summarization to the core • In the campus LANs, the distribution layer provides routing between VLANs • also apply security and QoS policies

  14. Roles of the Distribution Layer • Policy (for example, ensuring that traffic sent from a particular network is forwarded out one interface while all other traffic is forwarded out another interface) • Security filtering • Address or area aggregation or summarization • Departmental or workgroup access

  15. Roles of the Distribution Layer • Broadcast or 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 routing protocols) • Demarcation between static and dynamic routing protocols

  16. IOS & The Distribution Layer • Can use several Cisco IOS Software features to implement policy • Filtering by source or destination address • Filtering on input or output ports • Hiding internal network numbers by route filtering • Static routing • Quality-of-service (QoS) mechanisms (for example, ensuring that all devices along a path can accommodate the requested parameters)

  17. Access Layer • Provides user access to local segments on the network • characterized by switched- and shared-bandwidth LAN segments • Microsegmentation provides high bandwidth by reducing collision domains

  18. Roles of the Access Layer • High availability • Port security • Rate limiting • Address Resolution Protocol (ARP) inspection • Virtual access lists • Trust classification

  19. Hierarchical Model Summary • For (SOHO) environments, the entire hierarchy collapses to interfaces on a single device • Remote access to the central corporate network is through traditional WAN technologies

  20. Hierarchical Model Summary • Implement features such as dial-on -demand routing (DDR) and static routing to control costs • Remote access can include virtual private network (VPN) technology

  21. Hierarchical Model Examples

  22. Hierarchical Model Examples

  23. Enterprise CompositeNetwork Model • Facilitates the design of larger, more scalable networks • As networks become more sophisticated, it is necessary to use a more modular approach to design • The model divides the network into functional components • functional areas containing network modules

  24. Enterprise CompositeNetwork Model • It maintains the concept of distribution and access components • connects users, WAN services, and server farms through a high-speed campus backbone • In smaller networks, the layers can collapse into a single layer, even a single device

  25. Enterprise CompositeNetwork Model • The Enterprise Composite Network model divides the network into three major functional components: • Enterprise Campus • the campus infrastructure with server farms and network management • edge-distribution module provides distribution from the campus infrastructure to the Enterprise Edge

  26. Enterprise CompositeNetwork Model • Enterprise Edge • consists of the Internet, VPN, and WAN modules that connect the enterprise with the SP’s facilities • SP Edge • provides Internet, PSTN, and WAN services

  27. Enterprise CompositeNetwork Model

  28. Enterprise Campus Modules • The Enterprise Campus consists of the following • Enterprise infrastructure • Edge distribution • Server farms • Network management • Campus Infrastructure consists of core, building distribution, and access layers

  29. Enterprise Campus Modules • Server farm or data center provides high-speed access and high availability (redundancy) to the servers • CM (Call Manager) is located in the server farm for IP telephony networks

  30. Enterprise-Campus Model

  31. Enterprise-Campus Model • Can apply to small, medium, and large locations • large campus locations have a three-tier design with a wiring-closet component (building access layer), a building-distribution layer, and a campus-core layer • Small campus locations likely have a two-tier design with a wiring-closet component (Ethernet access layer) and a backbone core (collapsed core and distribution layers) • Medium-sized campus network designs sometimes use a three-tier implementation or a two-tier implementation, depending on needs

  32. Campus-Wide Design

  33. Campus-Wide Design • See Figure 3-6, page 56 • Workgroup switches in the building-access layer provide access to the network • Ports are assigned a VLAN for access • Trunking protocols connect building access, building distribution, and campus backbone switches • Multilayer switches and servers use FastEtherchannel or Gigabit Ethernet media

  34. Enterprise Edge Modules • The Enterprise Edge consists of the following modules: • E-commerce networks and servers • Internet connectivity • VPN and remote access • Classic WAN

  35. E-Commerce Module • Provides highly available networks for business services • Uses the high availability designs of the server-farm module with the Internet connectivity of the Internet module • Design techniques are the same as those described for these modules

  36. Internet Module • Several models connect the enterprise to the Internet • simplest form is to have a single circuit between the enterprise and the SP no redundancy or failover if the circuit fails!!

  37. Internet Module • You can use multihoming solutions to provide redundancy or failover for Internet service • Option 1: Single router, dual links to one Internet service provider (ISP) • Option 2: Single router, dual links to two ISPs • Option 3: Dual routers, dual links to one ISP • Option 4: Dual router, dual links to two ISPs

  38. Internet Module

  39. Internet Connectivity Solutions • Option 1 provides link redundancy but does not provide ISP and local router redundancy • Option 2 provides link and ISP redundancy but does not provide redundancy for a local router failure • Option 3 provides link and local router redundancy but does not provide for an ISP failure • Option 4 provides for full redundancy of the local router, links, and the ISPs

  40. VPN/Remote Access Module • Provides remote-access termination services, including authentication for remote users and sites • If you use a remote-access terminal server, this module connects to the PSTN network • Networks often prefer VPNs over remote-access terminal servers and dedicated WAN links • VPNs reduce communication expenses

  41. VPN Architecture

  42. WAN Module • The Enterprise Edge includes access to WANs. WAN technologies include the following: • Wireless • PSTN • Leased lines • Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) • PPP • Frame Relay • ATM • Cable • Digital subscriber line (DSL)

  43. Wan Module

  44. Service Provider (SP) Edge • The SP Edge consists of edge services such as the following: • Internet services • PSTN services • WAN services

  45. Service Provider (SP) Edge • Enterprises use SPs to acquire network services • ISPs offer enterprises access to the Internet • PSTN providers offer access to the global public voice network • WAN SPs offer Frame Relay, ATM, and other WAN services for Enterprise site-to-site connectivity

  46. Network Redundancy • If a customer has critical systems, assume that components will fail and plan accordingly • Workstation-to-router redundancy in the building-access layer • Server redundancy in the server farm module • Route redundancy within and between network components • Media redundancy in the access layer

  47. Workstation-to-Router Redundancy • When a workstation has traffic to send to a station that is not local, the workstation has many possible ways to discover the address of a router on its network segment • ARP • Some IP workstations send an ARP frame to find a remote station • A router running proxy ARP can respond with its data link layer address • Cisco routers run proxy ARP by default

  48. Workstation-to-Router Redundancy • Explicit configuration • Most IP workstations must be configured with the default gateway • If the workstation’s default router becomes unavailable, you must reconfigure the workstation with the address of a different router • Router Discovery Protocol (RDP) • RFC 1256 specifies an extension to the Internet Control Message Protocol (ICMP) • allows an IP workstation and router to run RDP to let the workstation learn the address of a router

  49. Workstation-to-Router Redundancy • RIP • An IP workstation can run RIP to learn about routers • Use RIP in passive mode • Usually in these implementations, the workstation is a UNIX system running the routed UNIX process

  50. Workstation-to-Router Redundancy • HSRP • Creates a phantom router that has its own IP and MAC addresses • Workstations use this phantom router as their default router • If the active router fails and the other HSRP routers stop receiving hello messages, the standby router takes over and becomes the active router

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