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Title: Switching Basics and Intermediate Routing CCNA 3 Chapter 5


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 FFFFFFFFFFFF

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 the OSI 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

51
LAN SwitchesAccess Layer Switches
  • Features of Access Layer Switches

52
LAN SwitchesAccess Layer Switches
  • Catalyst 1900 and 2820 switches were effective
    for small campus networks
  • The 2950 series provides access for users and
    servers that require higher bandwidth
  • Use FastEthernet and Gigabit Ethernet ports
  • The 4000 and 5000 series include Gigabit Ethernet
    ports
  • Effective in large campus networks

53
LAN SwitchesAccess Layer Switches
  • The Catalyst 4500 Series Is Often Used at the
    Access Layer in an Enterprise Network

54
LAN SwitchesDistribution Layer Overview
  • The distribution layer is between the access and
    core layers
  • Provides a boundary definition where packet
    manipulation can take place
  • Segments layers into broadcast domains
  • Can apply policies and access control lists to
    filter packets
  • Prevents problems at the access layer from
    affecting the core layer
  • Switches in this layer operate at Layer 2 and
    Layer 3

55
LAN SwitchesDistribution Layer Overview
  • Distribution layer functions
  • Aggregation of the wiring closet connections
  • Broadcast/multicast domain definition
  • VLAN routing
  • Any media transitions that need to occur
  • Security

56
LAN SwitchesDistribution Layer Overview
  • The Distribution Layer Is Typically Where Policy
    Is Incorporated

57
LAN SwitchesDistribution Layer Switches
  • Distribution layer switches are the aggregation
    points for multiple access layer switches
  • Must be able to accommodate the traffic from
    access layer devices
  • Must have high performance
  • Use Layer 2 and Layer 3 switching to delineate
    broadcast domains (multilayer switches that
    combine switching and routing functions)
  • Combine VLAN traffic
  • Focal points for decisions about traffic flow

58
LAN SwitchesDistribution Layer Switches
  • Distribution layer often used legacy Cisco
    switches
  • Catalyst 2926G
  • Catalyst 5000 series
  • Catalyst 6000 series
  • Current distribution layer switches
  • Catalyst 4500
  • Catalyst 4900
  • Catalyst 6500

59
LAN SwitchesDistribution Layer Switches
  • The Catalyst 6513 Is About as Good as it Gets
    for a Distribution Layer Switch, Circa 2006

60
LAN SwitchesCore Layer Overview
  • The core layer is a high-speed switching backbone
  • If the core switch does not have a routing
    module, an external router is used for the Layer
    3 function
  • This layer should not perform packet
    manipulation, such as access list filtering
  • Should have redundant paths
  • Current trend is to use wire-speed Layer 3
    switching at the core

61
LAN SwitchesCore Layer Overview
  • Core Layer is Devoted to High-Speed Switching of
    Numerous Packets

62
LAN SwitchesCore Layer Switches
  • Core Layer is the backbone of the campus switched
    network
  • Switches in this layer can use various layer 2
    technologies
  • Ethernet
  • ATM cell switching
  • The core layer can be a routed (Layer 3) core
  • Factors such as cost, need, and performance must
    be considered when choosing equipment

63
LAN SwitchesCore Layer Switches
  • Core Layer legacy switches
  • Catalyst 8500 series
  • IGX 8400 series
  • Lightstream 1010
  • Current core layer switches
  • Catalyst 6500 series
  • Cisco 12000 series routers
  • (occasionally) Cisco CRS-1 (Carrier Routing
    System) devices

64
Summary
  • LAN design typically focuses on
  • Functionality
  • Scalability
  • Manageability
  • Adaptability
  • Important elements of LAN design documentation
  • OSI topology map
  • LAN logical map
  • LAN physical map

65
Summary
  • Important elements of LAN design documentation
    (continued)
  • Cut sheets
  • VLAN logical map
  • Layer 3 logical map
  • Address maps
  • Layer 1 design issues include
  • Types of cables
  • Overall structure of the cabling
  • Media types such as Cat5, Cat5e, Cat6,
    single-mode fiber, and multi-mode fiber

66
Summary
  • The logical diagram of a LAN includes
  • MDF and IDF locations
  • Type and quantity of cables used to connect IDFs
    to MDF
  • Number of spare cables available to increase
    bandwidth between MDF and IDFs
  • Layer 2 devices provide flow control, error
    detection and error correction, and reduce
    congestion in a network
  • Microsegmentation of the network reduces the size
    of collision domains and reduces collisions

67
Summary
  • Characteristics of routers
  • Layer 3 devices
  • Create unique LAN segments
  • Allow communication between segments based on
    Layer 3 addresses (IP, usually)
  • Allow for segmentation of LAN into physical and
    logical networks
  • Allow for connectivity to WANs such as the
    Internet

68
Summary
  • VLAN implementation combines Layer 2 switching
    and Layer 3 routing technologies
  • Limit collision domains and broadcast domains
  • Originally used to create logical groupings
    according to function
  • Now more often used to group IP subnets
  • Routers or route processors enable communication
    between VLANs

69
Summary
  • The hierarchical design model includes three
    layers
  • Access layer gives access to users in workgroups
  • Distribution layer provides policy-based
    connectivity
  • Core layer provides optimal transport between
    sites
  • Access layer switches operate at Layer 2 of the
    OSI model
  • Offer services such as VLAN membership
  • Main purpose is to provide connectivity for end
    users
  • Should have low cost and high port density

70
Summary
  • Distribution layer switches delineate broadcast
    domains
  • Combines VLAN traffic
  • Focal point of decisions about traffic flow
  • Operate at both Layer 2 and Layer 3 of the OSI
    model (called multilayer switches)
  • Core layer switches provide a high-speed
    switching backbone
  • Should not be used for packet manipulation (no
    ACLs)
  • Should have redundant paths
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