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Switching Basics and Intermediate Routing CCNA 3 Chapter 5

Switching Basics and Intermediate Routing CCNA 3 Chapter 5. LAN Design Introduction. LAN design has become more difficult Due to multiple media types and LANs Complexity has increased Three aspects of a network that need to be identified before designing a large LAN:

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Switching Basics and Intermediate Routing CCNA 3 Chapter 5

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  1. Switching Basics and Intermediate Routing CCNA 3Chapter 5

  2. LAN DesignIntroduction • LAN design has become more difficult • Due to multiple media types and LANs • Complexity has increased • Three aspects of a network that need to be identified before designing a large LAN: • An access layer that connects end users to a LAN • A distribution layer that provides policy-based connectivity between end-user LANs • A core layer that provides the fastest connection between distribution points

  3. LAN DesignLAN Design Goals • Requirements of most networks designs: • Functionality: the network must work as intended • Scalability: the network must be expandable • Adaptability: the network must be designed with a vision toward future technologies • Manageability: the design must facilitate network monitoring and management to ensure stability

  4. LAN DesignLAN Design Considerations • A virtual LAN (VLAN) is a group of devices on one or more LANs that communicate as if they were attached to the same wire • To maximize bandwidth and performance, address these LAN design considerations: • Function and placement of servers • Collision domain issues • Segmentation issues • Broadcast domain issues

  5. LAN DesignLAN Design Considerations • Servers are usually dedicated to one function such as email or file sharing • Servers can be one of two types: • Enterprise servers support all users on the network • e-mail • Domain Name System (DNS), the Internet-wide system of mapping names to IP addresses • Workgroup servers support a specific set of users and offers services such as word processing and file sharing

  6. LAN DesignLAN Design Considerations • Enterprise servers are usually placed in the main distribution facility (MDF) • Traffic to enterprise servers should travel only to the MDF and not across other networks • Workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users who access the applications on these servers • Layer 2 switches in the MDF and IDF should have 1000Mbps (1Gbps) allocated bandwidth

  7. LAN DesignLAN Design Considerations Servers Are Typically Placed at a Point of Convergence in the Network, Such as Within an IDF or MDF

  8. LAN DesignLAN Design Considerations • Ethernet nodes use carrier sense multiple access with collision detection (CSMA/CD) • Each node must contend with all other nodes for access to the shared medium, or collision domain • If two nodes transmit at the same time, a collision occurs • The transmitted frames are destroyed and a jam signal is sent to all nodes on the segment • Excessive collisions reduce bandwidth

  9. LAN DesignLAN Design Considerations Collisions Increase Multiplicatively with the Number of Hosts

  10. LAN DesignLAN Design Considerations • Microsegmentation is when a single collision domain is split into smaller collision domains • Reduces number of collisions on a LAN segment • A broadcast occurs when the destination MAC address is FF:FF:FF:FF:FF:FF Single Broadcast Domain

  11. LAN DesignLAN Design Methodology • LAN design should be done in a set of systematic steps: • Step 1: Gather the requirements and expectations • Users • Corporate structure • Skill level of people • User attitudes towards computes and applications • Documented policies of the organization • Business information flow • Data that is mission critical • Protocols allowed on the network

  12. LAN DesignLAN Design Methodology • Step 1: Gather the requirements and expectations (continued) • Performance characteristics of current network • Types of desktops supported • Persons responsible for LAN addressing, naming, topology design, and configuration • Current topology • Human, hardware, and software resources • How resources are linked and shared • Financial resources of organization

  13. LAN DesignLAN Design Methodology • Documentation of requirements allows for an informed estimate of costs and timelines for implementation • Availability measures the usefulness of the network • Factors affecting availability: • Throughput • Response time • Access to resources • Customers may have different definitions of availability • As a network designer, goal is greatest availability at least cost

  14. LAN DesignLAN Design Methodology • Step 2: Analyze the requirements of the network and its users • Needs of users change • Need for bandwidth increases • Voice and video applications • The network must reliably provide prompt and accurate information • Information requirements of the users and organization must be met

  15. LAN DesignLAN Design Methodology • Step 3: Decide on the overall LAN topology that will satisfy user requirements • Star • Extended star (most common) The Star Topology is a Special Case of the Extended Star Topology

  16. LAN DesignLAN Design Methodology • Step 3: Decide on the overall LAN topology that will satisfy user requirements (continued) • LAN topology design has three unique OSI model categories: • Network layer (Layer 3) • Data link layer (Layer 2) • Physical layer (Layer 1) • By looking at theOSI layer, the design engineer can properly incorporate products and technologies

  17. LAN DesignLAN Design Methodology • Step 4: Document the physical and logical topology of the network • Physical topology: the way the network components are connected • Logical topology: the flow of data in the network, and the name and addressing schemes used

  18. LAN DesignLAN Design Methodology Logical Design Includes Name and Address Schemes

  19. LAN DesignLAN Design Methodology • Important elements of LAN design documentation: • OSI layer topology map • LAN logical map • LAN physical map • Cut sheets, which show cable runs • VLAN logical map • Layer 3 logical map • Address maps

  20. LAN DesignLAN Design Methodology Cut Sheet for IDF Location – Room XXX

  21. LAN DesignLAN Design Methodology VLAN Logical Design

  22. LAN DesignLAN Design Methodology IP Networks Are Displayed in a Layer 3 Logical Map

  23. LAN DesignLAN Design Methodology Address Maps Provide a Detailed View of IP Addresses for Key Devices and Interfaces

  24. LAN DesignLayer 1 Design • One of the most important design considerations is the cables • Most LAN cabling is based of FastEthernet or Gigabit Ethernet technology • Both can utilize full duplex technology, giving concurrent, collision-free, two-way communication • A logical bus topology that uses CSMA/CD can also be used with standard Ethernet

  25. LAN DesignLayer 1 Design • Design issues at Layer 1: • Type of cabling (copper or fiber optic) • 100BASE-TX specifies Cat5e unshielded twisted-pair (UTP), limited to 100m per segment • 100BAS-FX specifies multimode fiber with a length limit of 2 km • TIA/EIA-568-A standard details layout and wiring connection schemes • Media types: Cat5, Cat5e, Cat6 UTP and shielded twisted-pair (STP) that has shielding around wire pairs and another shield around all the wires in the cable, single-mode fiber, multi-mode fiber

  26. LAN DesignLayer 1 Design • Design issues at Layer 1 (continued): • Carefully evaluate strengths and weaknesses of topologies • Layer 1 issues cause most network problems • Use fiber-optic cable in the backbone and risers of a network • Use Cat5e or Cat6 in horizontal runs • Every device should be connected to a central location with a horizontal cabling run

  27. LAN DesignLayer 1 Design • In a simple star topology with only one wiring closet, the MDF includes one or more horizontal cross-connect (HCC) patch panels • HCC patch panels connect Layer 1 horizontal cabling with Layer 2 switch ports • The uplink port on the LAN switch is connected to the Ethernet port on the Layer 3 router with a patch cable

  28. LAN DesignLayer 1 Design HCC Connects Layer 1 Cabling to Layer 2 Switch Ports

  29. LAN DesignLayer 1 Design • When hosts in larger networks exceed the 100m distance limitation for Cat5e UTP, more than one wiring closet is required • Multiple wiring closets means you have multiple catchment areas • Secondary wiring closets are referred to as intermediate distribution facilities (IDFs)

  30. LAN DesignLayer 1 Design IDFs Connect via the MDF

  31. LAN DesignLayer 1 Design • Vertical cabling is also called backbone cabling • A vertical cross-connect interconnects IDFs to the central MDF • Fiber-optic cable is normally used for the VCC because cable lengths are longer than the100m limit for Cat5e cable

  32. LAN DesignLayer 1 Design VCC Interconnects IDFs to the MDF

  33. LAN DesignLayer 1 Design • The logical diagram is the basic road map of the LAN and includes these elements: • Location and identification of MDF and IDF wiring closets • Type and quantity of cables used to interconnect the IDFs with the MDF • Number of spare cables that are available to increase bandwidth between wiring closets • Detailed documentation of all cable runs, identification numbers, and port on which the run is terminated at the HCC or VCC • Essential for troubleshooting network problems

  34. LAN DesignLayer 2 Design • Purpose of Layer 2 devices is to switch frames based on destination MAC address • Collisions and collision domain size negatively affect network performance • Devices at Layer 2 (and Layer 3) determine the size of collision domains • Microsegmentation reduces the size of collision domains and is implemented through the use of switches

  35. LAN DesignLayer 2 Design LAN Switches Provide Microsegmentation

  36. LAN DesignLayer 2 Design • LAN switches allocate bandwidth on a per-port basis • This supplies more bandwidth to vertical cabling, uplinks, and servers • Referred to as asymmetric switching (provides switch connections between ports of unlike bandwidth) • Symmetric switching provides switched connections between ports of similar bandwidth

  37. LAN DesignLayer 2 Design • Desired capacity of vertical cable runs is greater than that of a horizontal cable run • 100 Mbps is adequate on a horizontal drop • Asymmetric LAN switches allow 100 Mbps and 1 Gbps on a single switch • Next task in the design process is to determine number of 100 Mbps and 1 Gbps ports needed in the MDF and every IDF • The number of hosts connected to a single port on a switch determines the size of the collision domain, affects bandwidth available to each host • Collision domains can be eliminated by using one host per switch port

  38. LAN DesignLayer 3 Design • A router is a Layer 3 device • Creates unique LAN segments • Allows communication between segments based on Layer 3 addresses, such as IP addresses • Allows segmentation of LAN into unique physical and logical networks • Allows for connectivity to WANs, such as the Internet • Forwards data packets based on destination addresses • Does not forward broadcasts • Is the entry and exit point for a broadcast domain

  39. LAN DesignLayer 3 Design • When to use a router: • If the problem is a protocol issue instead of a contention issue • If there are excessive broadcasts on the LAN • If a higher level of security is needed • However, Layer 3 switches can now perform many of these functions at nearly the same cost • Expect Layer 3 switching to become pervasive in 10 years • Layer 3 switches perform wire-speed routing, QoS, and security functions

  40. LAN DesignLayer 3 Design Logical Addressing Mapped to the Physical Network

  41. LAN DesignLayer 3 Design Logical Network Addressing Map

  42. LAN DesignLayer 3 Design Physical Network Maps Ease Troubleshooting

  43. LAN DesignLayer 3 Design • VLAN implementation combines Layer 2 switching and Layer 3 routing technologies • Limits collision and broadcast domains • Provides security with creation of VLAN groups that communicate only through a router • Ports on a switch are assigned to different VLANs

  44. LAN DesignLayer 3 Design VLANs Are Essentially Switch Port Groupings

  45. LAN SwitchesIntroduction • Early LAN switches did not support VLANs • Second-generation switches supported VLANs, but relied on routers for inter-VLAN communication • Third generation switches have the route processors built into the switches • With the exception of access layer switches, switches are becoming almost indistinguishable from routers

  46. LAN SwitchesSwitched LANs and the Hierarchical Design Model • Use of a hierarchical design model makes it more likely to meet the needs of a medium or large organization • Layers of the hierarchical model: • Access layer: gives users access to the network • Distribution layer: provides policy-based connectivity • Core layer: provides optimum transport between sites; often referred to as the backbone

  47. LAN SwitchesAccess Layer Overview • Entry point to network for user workstations and servers • Functions include MAC layer filtering and microsegmentation • Layer 2 switches are used

  48. LAN SwitchesAccess Layer Overview The Access Layer is an Entry Point to the Network, Particularly for End Users

  49. LAN SwitchesAccess Layer Switches • Access layer switches generally operate at Layer 2 of the OSI model • Provide services such as VLAN membership • Main purpose is to connect end users • Should do this with low cost and high port density

  50. LAN SwitchesAccess Layer Switches • Common legacy access layer switches used today • Catalyst 1900 series • Catalyst 2820 series • Catalyst 2950 series (not a legacy switch) • Catalyst 4000 series • Catalyst 5000 series

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