CIS 460

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CIS 460 Network Analysis and Design

• Chapter 3 Characterizing the Existing
  Internetwork

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Characterizing the Existing Network

• Examine the customers existing network to better
  judge how to meet expectations for network
  scalability, performance and availability
• Understanding the existing networks structure,
  uses, and behavior you get a better feel if the
  design goals are realistic
• Most designers design network enhancements to
  existing networks

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Characterizing the Network Infrastructure

• Develop a network map
• Learning location of major internetworking
  devices and network segments
• Documenting the names and addresses of major
  devices and segments
• Documenting the types and lengths of physical
  cabling
• Investigating architectural and environmental
  constraints

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Developing a Network Map

• Location of major hosts, interconnection devices
  and network segments
• Help understand traffic flow
• Data on performance characteristics of network
  segments coupled with location information gives
  insight to where users are concentrated and the
  level of traffic to be supported
• Goal is to obtain a map of the already-implemented
  network

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Tools for Developing Network Maps

• Invest in a good network-diagramming tool
• Visio is one example
• Some companies offer diagramming and network
  documentation tools that automatically discover
  existing networks.

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What Should a Network Map Include?

• Geographical countries, states, provinces,
  cities and campuses
• Wan connections between countries, states, and
  cities
• Buildings and floors and rooms or cubicles if
  possible
• WAN and LAN connections between buildings and
  campuses

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What should a network map include? (Contd)

• Indication of the data-link technology for WANs
  and LANs
• Service provider for WANs
• Location of routers and switches
• Virtual Private Networks
• Major servers or server farms
• Location of major network-management stations
• Location and reach of any virtual LANs

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What should a network map include? (Contd)

• Topology of any firewall security system
• Location of any dial-in and dial out systems
• Indication of where workstations reside
• Depiction of the logical topology or architecture
  of the network

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Characterizing Network Addressing and Naming

• Documenting any strategies customer has for
  networking addressing and naming
• On detailed network maps include the names of
  major sites, routers, network segments and
  servers
• Investigate the network-layer addresses your
  customer uses
• A customer goal might be to use route
  summarization
• Existing addressing scheme might affect the
  routing protocols you can select

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Characterizing Wiring and Media

• Document existing cabling design to help plan for
  enhancements and identify any potential problems
• Assess who well equipment and cables are labeled
• Document connections between buildings (number of
  pairs of wire and type)
• Locate telecommunications wiring closets,
  cross-connect rooms and any lab or computer rooms
• Use the chart in Table 3-1 on page 61.

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Checking Architectural and Environmental
Constraints

• Pay attention to environmental during cabling
  investigation
• Flooding, right of way issues, heavy equipment
  usage
• Building issues

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Checking the Health of the Existing Internetwork

• Knowing baseline of existing system give a
  standard to measure new system against
• Existing segments will effect overall network
  performance
• Segments that will interoperate with new
  segments, backbone networks and networks that
  connect old and new areas
• Legacy systems may have to be included

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The Challenges of Developing a Baseline of
Network Performance

• Not an easy task
• Time selection
• Time allocation
• Typical time period
• Periods of normal traffic laod
• Customer may not recognize need
• Need good understanding of customers technical
  and business goals

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Analyzing Network Availability

• Gather statistics on MTBF and MTTR
• Learn about causes of the most recent and most
  disruptive periods of downtime
• Document availability in a Table such as Table
  3-2 on page 65

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Analyzing Network Utilization

• A measure of how much bandwidth is in use during
  a specific time interval
• Usually a percentage of capacity
• Different tools use different averaging windows
• Use appropriate division of time
• Averaged over too short or long a period can be
  misleading
• It is always better to error on the side of
  gathering too much data

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Bandwidth Utilization by Protocol

• Measure by broadcast versus unicast traffic
• By each major protocol
• Some protocols send excessive broadcast traffic
• Use a protocol analyzer on each major network
  segment
• Relative usage specifies how much bandwidth is
  used by the protocol in comparison to total
  bandwidth currently in use by the segment.
• Absolute usage specifies how much bandwidth is
  used by the protocol in comparison to the total
  capacity of the segment
• Document using a Table such as 3-3 on page 69

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Analyzing Network Efficiency

• Use a bit error rate tester on serial lines to
  test number of damaged bits compared to total
  bits
• On packet-switched networks measure frame errors
  because a whole frame is bad if a single bit is
  changed or dropped. Utilizes cyclic redundancy
  check (CRC) based on bits in a frame
• A protocol analyzer can check the CRC on received
  frames

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Analyzing Network Efficiency (Contd)

• Errors increase as utilization increases so
  document errors as function of the number of
  bytes seen by the monitoring tool
• Some monitors allow you to print the top 10
  stations sending frames
• Baseline analysis should also include
  upper-layer problems
• Accuracy should also include a measurement of
  lost packets

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Analyzing ATM Errors

• Accuracy is measure in terms of cell error ration
  (CER), cell loss ration (CLR), cell misinsertion
  rate (CMR) and severely errored cell block ration
  (SECBR)
• CER is number of errored cells divided by total
  number of successfully transferred cells plus
  errored cells
• CMR is caused by an undetected error in the
  header of a cell
• If no tool, check the performance by analyzing
  the level of frame errors and upper-level
  problems

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Analyzing Network Efficiency

• Bandwidth utilization is optimized when
  applications and protocols are configured to send
  large amounts of data per frame.
• The goal is to maximize the number of data bytes
  compared to the number of bytes in headers and in
  acknowledgment packets
• Use a protocol analyzer to examine the current
  frame sizes on the network
• Analyzing frame sizes can help understand health
  of a network, not just the efficiency

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Analyzing Delay and Response Time

• Measure response time between significant network
  devices before and after a new network design is
  implemented
• Send ping packets and measure time to send and
  respond
• Document using a Table such as 3-4 on page 75
• Measure response time from a user point of view
• Test user applications and system protocols
• Do some testing when the system is experiencing
  problems or change

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Checking the Status of Major Routers

• Includes determining how busy the router is, how
  many packets the router has processed, how many
  packets the router has dropped and the status of
  buffers and queues.
• You can use the Simple Network Management
  Protocol (SNMP) to check the health of a router
• To check the health of a router you need to check
  the router variable on a regular basis over a few
  days

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Tools for Characterizing the Existing Internetwork

• Protocol Analyzers
• Remote Monitoring Tools
• Cisco Tools for characterizing an Existing
  Internetwork
• Cisco Discovery Protocol
• Enterprise Accounting for NetFlow
• Netsys Service-Level Management Suite
• Cisco Works
• Other Tools

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Protocol Analyzers

• A fault-and-performance-management tool that
  captures network traffic, decodes the protocols
  in the captured packets and provides statistics
  to characterize load, errors, and response time.
• Sniffer Network Analyzer
• EtherPeek

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Remote Monitoring Tools

• Remote Monitoring (RMON) MIB developed to
  overcome shortcomings in the standard SNMP MIB
  for gathering statistics on data-link and
  physical-layer parameters
• Gathers statistics on CRC errors, Ethernet
  collisions, Token-ring soft errors, frame sizes,
  number of packets in and out of a device, and the
  rate of broadcast packets
• The RMON MIB alarm group allows a network manager
  to set thresholds for network parameters and
  automatically delivers alerts to management

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Cisco Tools for Characterizing an Existing
Internetwork

• Cisco has a complete range of tools for
  characterizing an existing internetwork, ranging
  from the Cisco Discovery Protocol to
  sophisticated Netsys tools

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Cisco Discovery Protocol

• Specifies a method for Cisco routers and switches
  to send configuration information to each other
  on a regular basis
• Look at information about neighboring routers
• Protocols enabled
• Network address for enabled protocols
• Number and types of interfaces
• Type of platform and its capabilities
• Version of Cisco IOS software

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Enterprise Accounting for NetFlow

• Can help understand bandwidth usage and
  allocation, quality of service levels, ro8uter
  usage, and router port usage
• Recognizes network flows and characterizes
  network and router usage by user (IP address),
  application, and department

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Netsys Service-Level Management Suite

• Enables defining, monitoring, and assessing
  network connectivity, security, and performance.
• Particularly useful for characterizing an
  existing network as part of a network design
  proposal

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Cisco Works

• A series of SNMP-based internetworking management
  software application for device monitoring,
  configuration maintenance, and troubleshooting of
  Cisco devices

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Other Tools for Characterizing an Existing
Internetwork

• Many other tools out there. Visit various web
  sites identified in the book to look at some of
  the tools.

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Conclusion

• Use a network health checklist like the one on
  page 81 to assist in verifying the health of an
  existing network.