Transcript Characterizing the Existing Internetwork

CIS 460 – Network Analysis and
Design
Chapter 3 – Characterizing the
Existing Internetwork
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 network’s structure,
uses, and behavior you get a better feel if the
design goals are realistic
• Most designers design network enhancements to
existing networks
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
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 alreadyimplemented network
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.
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
What should a network map
include? (Cont’d)
• 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
What should a network map
include? (Cont’d)
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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
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
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, crossconnect rooms and any lab or computer rooms
• Use the chart in Table 3-1 on page 61.
Checking Architectural and
Environmental Constraints
• Pay attention to environmental during
cabling investigation
• Flooding, right of way issues, heavy
equipment usage
• Building issues
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
The Challenges of Developing a
Baseline of Network Performance
• Not an easy task
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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
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
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
Bandwidth Utilization by
Protocol
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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
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
Analyzing Network Efficiency
(Cont’d)
• 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
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
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
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
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
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
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
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
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
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:
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Protocols enabled
Network address for enabled protocols
Number and types of interfaces
Type of platform and its capabilities
Version of Cisco IOS software
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
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
Cisco Works
• A series of SNMP-based internetworking
management software application for device
monitoring, configuration maintenance, and
troubleshooting of Cisco devices
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.
Conclusion
• Use a network health checklist like the one
on page 81 to assist in verifying the health
of an existing network.