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CSE 550 Computer Network Design

CSE 550 Computer Network Design. Dr. Mohammed H. Sqalli COE, KFUPM Spring 2007 (Term 062). Outline. Network Topology Design Flat Network Topologies Hierarchical Network Design Model Mesh Network Topologies Redundant Network Design Topologies Modular Network Design Model

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CSE 550 Computer Network Design

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  1. CSE 550Computer Network Design Dr. Mohammed H. Sqalli COE, KFUPM Spring 2007 (Term 062)

  2. Outline • Network Topology Design • Flat Network Topologies • Hierarchical Network Design Model • Mesh Network Topologies • Redundant Network Design Topologies • Modular Network Design Model • Campus/LAN Network Design Topology • Enterprise/WAN Network Design Topology • Secure Network Design Topologies Lecture Notes - 6

  3. Network Topology Design

  4. Network Topology Design • First step in the logical design phase of the top-down network design methodology • During this phase, we identify: • Networks and interconnection points • Size and scope of networks • Types of internetworking devices required Lecture Notes - 6

  5. Network Topology Design • Questions to determine network topology: • Is it a small LAN with few workstations? • Is it a campus LAN or a massive enterprise implementation? • Is scalability important? • How about network management? • What about cost? Lecture Notes - 6

  6. Network Topology Design • No one topology is right for every network environment • Each network topology can be an integral part of another topology design • Redundant and secure topologies should be part of every network design Lecture Notes - 6

  7. Network Topologies • Network topologies covered: • Flat • Hierarchical • Mesh • Redundant • Campus/LAN • Enterprise/WAN • Secure Lecture Notes - 6

  8. Flat Network Topologies

  9. Flat Network Topologies • Generally used for very small networks • Each network device (e.g., hub, switch, …) is used for a general rather than specific purpose • Most network components are used for simple broadcasting and providing limited switching capabilities • Based on a common broadcast domain • There is no hierarchy • Not generally created in a modular fashion • Provide a consistent and easy-to-manage network environment • Scalability is not usually an importantdesign factor Lecture Notes - 6

  10. Flat Network Topologies- Advantages - • Lower initialcost – due to the smaller size of network and lowerequipmentcosts • Special routing and switching components are not used to a wide extent • Reliability – due to the simplistic design and general static nature of the topology • Easy to design – due to the lack of need for modularity and scalability • Easy to implement – due to the lack of specialized switching equipment • Easy to maintain – as long as the network stays small Lecture Notes - 6

  11. Flat Network Topologies- Disadvantages - • Not modular – changes to the environment will usually affect all internetworking devices • Bandwidth domain – most if not all devices are usually in the same bandwidth domain (i.e., share the same bandwidth) • Broadcast domain – same broadcast domain that can lead to congestion • Lack of hierarchy makes troubleshooting difficult – inspect the entire network Lecture Notes - 6

  12. Flat WAN Topologies • Flat loop topology: A WAN for a small company may consist of a few sites connected in a loop • Meets goals for low cost and reasonably good availability • Quick convergence of routing protocols • Communication recovery when one link fails • Not recommended for networks with many sites: • Significant delay and a higher probability of failure because of routers that are many hops away Lecture Notes - 6

  13. Flat vs. Hierarchical WAN Topologies • Hierarchical redundant topology meets goals for scalability, high availability, and low delay Lecture Notes - 6

  14. Hierarchical Network Design Model

  15. Hierarchical Network Design Model (1/2) • When scalability is a major goal, a hierarchicaltopology is recommended • Created in layers to allow specific functions and features to be implemented in each of the layers • Each component is carefully placed in a hierarchical design for maximum efficiency and specific purpose • Routers, switches, and hubs all play specific role in routing and distributing data and packet information • The model can be used for switched networks as well as routed networks Lecture Notes - 6

  16. Hierarchical Network Design Model (2/2) • Incorporates 3 key layers (Three-tier hierarchical model): • Core layer • Distribution layer • Access layer • Each layer has a specific role • Each layer provides a backbone for the layer below • Definition: A backbone is a network whose primary purpose is the interconnection of other networks Lecture Notes - 6

  17. Three-layer Hierarchical Topology (1/4) Lecture Notes - 6

  18. Three-layer Hierarchical Topology (2/4) A Partial-Mesh Hierarchical Design Lecture Notes - 6

  19. Three-layer Hierarchical Topology (3/4) Lecture Notes - 6

  20. Three-layer Hierarchical Topology (4/4) Lecture Notes - 6

  21. Three-layer Hierarchical Topology- Core Layer (1/3) - • Main rule:Design the core layer for optimized transport between sites • Should be optimized for low latency and good manageability • Consists of high-end routers and switches that are optimized for availability and performance • Focus on redundancy and reliability • Adapt to changes quickly and continue to function with circuit outages • Should have a limited and consistent diameter • Provides predictable performance and ease of troubleshooting Lecture Notes - 6

  22. Three-layer Hierarchical Topology- Core Layer (2/3) - • Provides optimal wide-area transport between geographically remote sites • Connects campus networks in a corporate or enterprise WAN • Services are typically leased from a telecom service provider • Need to efficiently use bandwidth because of provider tariffs • May use the public Internet as enterprise backbone Lecture Notes - 6

  23. Three-layer Hierarchical Topology- Core Layer (3/3) - • Includes one or more links to external networks (for extranet or Internet connections). This centralization at the core: • Reduces complexity and potential of routing problems • Minimizes security concerns, due to having only one security structure to administer • Means higher bandwidth costs • Avoid using packet filters or other features that slow down the manipulation of packets • Avoid connecting end stations to the core Lecture Notes - 6

  24. Three-layer Hierarchical Topology- Distribution Layer (1/3) - • Main rule:Connect network services and implement policies at the distribution layer • Demarcation point between access and core layers • Acts as a concentrator point for many of its access layer sites • Delineates broadcast domains (can be done at the access layer as well) • Can be configured to route between VLANs • Connects multiple networks (departments) within a campus network environment (one or more buildings) • Includes campus backbone network, based on FDDI, Fast Ethernet, Gigabit Ethernet, or ATM • Connects network services to the access layer Lecture Notes - 6

  25. Three-layer Hierarchical Topology- Distribution Layer (2/3) - • Links usually owned and/or controlled by the organization • Network policies are often implemented in this layer: • Consists of routers and switches that implement policies • Network security: • Firewall, filtering, encryption • Access to services (admin privileges, etc.) • Traffic patterns through definition of path metrics (priority, preference, trust, etc) • Route summarization / Address aggregation • Network naming and numbering conventions • Traffic loading, routing, and address translation Lecture Notes - 6

  26. Three-layer Hierarchical Topology- Distribution Layer (3/3) - • Controls access to resources for security reasons • Controls network traffic that traverses the core for performance reasons • Redistribute between bandwidth-intensive access layer routing protocols (e.g., IGRP), and optimized core routing protocols (e.g., EIGRP) • Should hide detailed topology information about the access layer from core routers • Maximizes hierarchy, modularity, and performance (e.g., route summarization) • Should hide detailed topology information about the core layer from the access layer (e.g., use one default route) Lecture Notes - 6

  27. Three-layer Hierarchical Topology- Access Layer (1/3) - • Main rule:Move users down to the access layer • Provides end-user access to a network • Where hosts are attached to the network (e.g., labs) • Usually a LAN or a group of LANs • Usually within a single building (or single floor) • Typically uses Ethernet, Token Ring, or FDDI • Can include routers, switches, bridges, shared-media hubs, and wireless access points Lecture Notes - 6

  28. Three-layer Hierarchical Topology- Access Layer (2/3) - • Connects workgroups (e.g., marketing, administration) • Can be divided into two levels (workgroup level and desktop level) • Workgroup level: e.g., departmental level • Desktop level: where end-user devices are attached • Provides logical network segmentation, traffic isolation, and distributedenvironment • Remote (dialup) users are connected at this tier Lecture Notes - 6

  29. Three-layer Hierarchical Topology- Access Layer (3/3) - • In a campus network, it provides switches or hubs for end-user access • Connects users via lower-end switches and wireless access points • Switches are used to divide up bandwidth domains to meet the specific demands of certain applications (e.g., multimedia) • In a WAN design, it consists of the routers at the edge of the campus networks • Provides remote access into the corporate internetwork using WAN technologies, e.g., ISDN, Frame Relay, etc. • Can implement routing features, e.g., dial-on-demand (DDR) routing Lecture Notes - 6

  30. Hierarchical Network Design- Guidelines (1/3) - • Choose a hierarchical model that best fits your requirements • Do not always completely mesh all tiers of the network (use the backbone for connections) • Coreconnectivity, however, will generally be meshed for circuit redundancy and network convergence speed • Do not place end stations on backbones • Improves the reliability of the backbone • Workgroup LANs should keep as much as 80% oftheir traffic local to the workgroup • Right positioning of the servers • Use specific features at the appropriate hierarchical level Lecture Notes - 6

  31. Hierarchical Network Design- Guidelines (2/3) - • Control the diameter of a hierarchical enterprise network topology (in most cases, 3 major layers are sufficient) • Provides low and predictable latency • Helps predict routing paths, traffic flows, and capacity requirements • Makes troubleshooting and network documentationeasier • Design the access layer first, then the distribution layer, and finally the core layer • Helps, more accurately, perform capacity planning at the distribution and core layers Lecture Notes - 6

  32. Hierarchical Network Design- Guidelines (3/3) - • Avoid chains at the access layer (e.g., connecting a branch network to another branch, adding a 4th layer) • Avoid backdoors (i.e., connection between devices in the same layer) • Cause unexpected routing problems • Make network documentation and troubleshootingmoredifficult Lecture Notes - 6

  33. Hierarchical Network Design Guidelines- A Chain and A Backdoor at the Access Layer - Lecture Notes - 6

  34. Three-layer Hierarchical Topology- Advantages (1/4) - • Modularity: • Keeps each design element simple and easy to understand • Allows each component to perform a specific purpose in the internetwork • Easier and more organized network management • Enables creating designelements that can be replicated as the network grows  Scalability • Example: Planning a campus network for a new site might simply mean replicating an existing campus network design • Scalability: • Allows addition of routers, switches, etc. when needed with minimum impact to design • Hierarchical networks are built for maximum scalability • As elements in a network require change, the cost of an upgrade is contained to a small subset of the network Lecture Notes - 6

  35. Three-layer Hierarchical Topology- Advantages (2/4) - • Predictability: • Makes capacity planning for growth easier • Manageability: • Easy to deploy network management instrumentation by placing probes at different levels of hierarchy • More automated • Ease of troubleshooting: • Fault isolation is improved because network technicians can easily recognize the transition points in the network to help isolate possible failure points • Use “divide-and-conquer” approach: • Temporarily segment the network • Does not affect core tier network Lecture Notes - 6

  36. Three-layer Hierarchical Topology- Advantages (3/4) - • Ease of implementation: • Phased approach is more effective due to cost of resources • Efficient allocation of resources in each phase of network deployment • Simplicity: • Minimizes the need for extensive training for network operations personnel • Testing a network design is made easy because there is clear functionality at each layer • Protocol support: • Mixing new protocols is easier • Merger of companies using different protocols is easier Lecture Notes - 6

  37. Three-layer Hierarchical Topology- Advantages (4/4) - • High availability: • Due to redundancy, alternate paths, optimization, and filtering • Low delay: • Routers delineating broadcast domains • Multiple paths for switching and routing • Cost efficient: • Due to ability to optimize and tune switching and routing paths • Today’s fast-converging routing protocols were designed for hierarchical topologies • Route summarization is facilitated by hierarchical network design Lecture Notes - 6

  38. Three-layer Hierarchical Topology- Disadvantages - • Cost – due toredundancy that is often integrated into the network topology and switching equipment Lecture Notes - 6

  39. Three-layer Hierarchical Model- Variations - • One-tier Design – Distributed • One-tier Design – Hub-and-Spoke • Two-tier Design Lecture Notes - 6

  40. Three-layer Hierarchical Model- One-tier Design – Distributed - • Remote networks connect to a pseudo-core • Good for small networks with no centralized server location • Advantage:Faster overall response time between peers, simplicity, and cost effectiveness • Disadvantage:Loss of centralized management control and higher management cost because of duplicated management functions • Responsibilities such as server backups and network documentation are delegated to the access site Lecture Notes - 6

  41. Three-layer Hierarchical Model- One-tier Design – Hub-and-Spoke - • Servers are located in central farms • Advantage:Increased management control (centralized) • Disadvantage:Single points of failure and bandwidth aggregation Lecture Notes - 6

  42. Three-layer Hierarchical Model- A Hub-and-Spoke Hierarchical Topology - Lecture Notes - 6

  43. Three-layer Hierarchical Model- Two-tier Design - • A campus backbone that interconnects separate buildings • VLANs can be used to create separate logical networks (i.e., broadcast domains) Lecture Notes - 6

  44. How Can You Tell When You Have a Good Design? (P. Welcher) • When you already know how to add a new building, floor, WAN link, remote site, e-commerce service, and so on • When new additions cause only local change, to the directly connected devices • When your network can double or triple in size without major design changes • When troubleshooting is easy because there are no complex protocol interactions to wrap your brain around Lecture Notes - 6

  45. Mesh Network Topologies

  46. Mesh Network Topologies • Network designers often recommend a mesh topology to meet availabilityrequirements • Constructed with many different interconnections between network nodes • Two types: • Full-mesh topology • Partial-mesh topology Lecture Notes - 6

  47. Mesh Network Topologies- Full-Mesh Topology (1/3) - • Every router or switch is connected to every other router or switch • Provides complete redundancy and excellent reliability • Offers good performance • Nodes are typically located at core level or backbone level of the enterprise network Lecture Notes - 6

  48. Mesh Network Topologies- Full-Mesh Topology (2/3) - • Frequently supports mission-critical services and applications • Cannot guarantee that server or application failures will be avoided with just a fully meshed backbone • Not a cost-effective solution • High number of links: (N*(N-1))/2 for N routers of switches Lecture Notes - 6

  49. Mesh Network Topologies- Full-Mesh Topology (3/3) - Lecture Notes - 6

  50. Mesh Network Topologies- Partial-Mesh Topology (1/2) - • Has fewer connections than full-mesh topology • Each network node or switch does not necessarily have immediate connection to each other network node or switch • To reach another router, the network might require traversing intermediate links • Can still provide redundancy through alternate paths • Allows mission critical applications to continue processing • If a network connection fails, the network will remain operational with reduced bandwidth and service levels • More likely to be implemented in an enterprisenetwork Lecture Notes - 6

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