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Top-Down Network Design Chapter Three Characterizing the

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					 Top-Down Network
           Design

                 Chapter Three

Characterizing the Existing Internetwork




             Copyright 2004 Cisco Press & Priscilla Oppenheimer
Objectives


             To judge how to meet expectations for network scalability,
 1           performance, and availability

               To learn about the topology and physical structure, and
     2         assessing the network’s performance

                To describe techniques and tools in characterizing an
         3
                incumbent network
What’s the Starting Point?
 • According    to Abraham Lincoln:
   •   “If we could first know where we are
       and whither we are tending, we could
       better judge what to do and how to do
       it.”
Where Are We?
•   Characterize the exiting internetwork in
    terms of:
     •   Its infrastructure
           • Logical structure (modularity, hierarchy,
             topology)
           • Physical structure
     • Addressing and naming
     • Wiring and media
     • Architectural and environmental
       constraints
     • Health
                Get a Network Map
  Medford                                                                                 Roseburg
Fast Ethernet                                                                            Fast Ethernet
  50 users                                                                                 30 users
                             Frame Relay                Frame Relay
                            CIR = 56 Kbps              CIR = 56 Kbps
                               DLCI = 5                   DLCI = 4




                                            Gigabit                             Grants Pass
                                                                                    HQ
                                            Ethernet                             16 Mbps
            Grants Pass                                                         Token Ring
                 HQ
            Fast Ethernet
              75 users
                                                                                               FEP
                                                                                         (Front End
                                                                                         Processor)

                                                                                                IBM
                                                                                          Mainframe
                                     T1

                                                               Web/FTP server
         Eugene
         Ethernet                                                      T1            Internet
         20 users
Get a Network Map: Purpose
• Learn the location of major hosts,
  interconnection devices, and network
  segments for better understanding of traffic
  flow.
• Remember! Your aim at this step is to obtain a
  map (or set of maps) of the already-
  implemented network.
• You are one step ahead if the customers are
  already have maps for the new network
  design designer have to check the detailed
  analysis of business and technical
  requirements
Characterize Addressing and Naming

 • IP addressing for major devices, client
   networks, server networks, and so on
 • Any addressing oddities, such as
   discontiguous subnets?
 • Any strategies for addressing and
   naming?
     •   For example, sites may be named using
         airport codes
          • San   Francisco = SFO, Oakland = OAK
Discontiguous Subnets
                              Area 0
                             Network
                           192.168.49.0

  Router A                                              Router B

          Area 1                                 Area 2
   Subnets 10.108.16.0 -                  Subnets 10.108.32.0 -
       10.108.31.0                            10.108.47.0


   Discontiguous subnets : two or more portions of a major
   network that are divided by another major network.
•Characterize the Wiring and Media
• Single-mode fiber
• Multi-mode fiber
• Shielded twisted pair (STP) copper
• Unshielded-twisted-pair (UTP) copper
• Coaxial cable
• Microwave
• Laser
• Radio
• Infra-red
Campus Network Wiring
                         Horizontal        Work-Area
                          Wiring            Wiring

                                      Wallplate
             Telecommunications
                 Wiring Closet




  Vertical
   Wiring
 (Building
Backbone)




                                  Main Cross-Connect Room                   Intermediate Cross-Connect Room
                                  (or Main Distribution Frame)              (or Intermediate Distribution Frame)




                                                                  Campus
                 Building A - Headquarters                       Backbone                  Building B
Architectural Constraints

• Make   sure the following are sufficient
  • Air conditioning
  • Heating

  • Ventilation

  • Power

  • Protection from electromagnetic
    interference
  • Doors that can lock
Architectural Constraints
• Make   sure there’s space for:
  • Cabling conduits
  • Patch panels

  • Equipment racks

  • Work areas for technicians installing
    and troubleshooting equipment
Issues for Wireless Installations
•   Reflection-Reflection causes the signal to bounce
    back on itself.
•   Absorption-Some of the electromagnetic energy of
    the signal can be absorbed by the material in objects
    through which it passes, resulting in a reduced signal
    level.
•   Refraction-When an RF signal passes from a medium
    with one density into a medium with another density,
    the signal can be bent, much like light passing through
    a prism.
•   Diffraction-similar to refraction, results when a region
    through which the RF signal can pass easily is adjacent
    to a region in which reflective obstructions exist.
Check the Health of the Existing
Internetwork
 • Performance
 • Availability
 • Bandwidth utilization
 • Accuracy
 • Efficiency
 • Response time
 • Status of major routers, switches, and
   firewalls
 Characterize Availability

                           Date and Duration   Cause of
             MTBF   MTTR   of Last Major       Last Major
                           Downtime            Downtime


Enterprise


Segment 1


Segment 2


Segment n
Network Utilization in Minute Intervals

                               Network Utilization

        16:40:00

        16:43:00

        16:46:00

        16:49:00

        16:52:00
 Time




        16:55:00                                                     Series1

        16:58:00

        17:01:00

        17:04:00

        17:07:00

        17:10:00
                   0   1   2       3                 4   5   6   7
                                       Utilization
Network Utilization in Hour Intervals
                                       Network Utilization


        13:00:00



        14:00:00
 Time




        15:00:00                                                                 Series1



        16:00:00



        17:00:00


                   0   0.5   1   1.5        2        2.5     3   3.5   4   4.5
                                            Utilization
   Bandwidth Utilization by Protocol

             Relative      Absolute                  Multicast
                                         Broadcast
             Network       Network                   Rate
                                         Rate
             Utilization   Utilization


Protocol 1


Protocol 2


Protocol 3


Protocol n
Characterize Packet Sizes
 Characterize Response Time


         Node A   Node B   Node C   Node D


          X
Node A

                   X
Node B


Node C                      X


Node D                                X
Check the Status of Major Routers,
Switches, and Firewalls
• show buffers
• show environment

• show interfaces

• show memory

• show processes

• show running-config

• show version
Tools
• Protocol analyzers
• Multi Router Traffic Grapher (MRTG)
• Remote monitoring (RMON) probes
• Cisco Discovery Protocol (CDP)
• Cisco IOS NetFlow technology
• CiscoWorks
• Cisco IOS Service Assurance Agent (SAA)
• Cisco Internetwork Performance Monitor
  (IPM)
Sample of tables to be used
 Table3-1 Building Wiring
Summary
• Characterize the exiting internetwork
  before designing enhancements
• Helps you verify that a customer’s design
  goals are realistic
• Helps you locate where new equipment
  will go
• Helps you cover yourself if the new
  network has problems due to unresolved
  problems in the old network
Review Questions
• What factors will help you decide if the existing
  internetwork is in good enough shape to support
  new enhancements?
• When considering protocol behavior, what is the
  difference between relative network utilization
  and absolute network utilization?
• Why should you characterize the logical
  structure of an internetwork and not just the
  physical structure?
• What architectural and environmental factors
  should you consider for a new wireless
  installation?

				
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