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TOP-DOWN NETWORK DESIGN
CHAPTER THREE
CHARACTERIZING THE EXISTING INTERNETWORK
Oppenheimer
To judge how to meet expectations for network scalability, performance, and availability
OBJECTIVES
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To learn about the topology and physical structure, and assessing the network’s performance
To describe techniques and tools in characterizing an incumbent network
THE EXISTING NETWORK
We now know where we want to go based on the analysis that was just done
We next need to determine where we are starting from
If this is an entirely new network, this step does not need to be done
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CHARACTERIZING THE NETWORK INFRASTRUCTURE
•Developing a set of network maps and learning the location of major internetworking devices and network segments.
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DEVELOPING A NETWORK MAP
Need to understand the traffic flow by learning the location of major hosts, interconnecting devices and network segments.
Goal is to obtain the network map/maps of the already implemented network.
Tools for developing network map:
Some customer don’t have existing map
Find good network-diagramming tool i.e. Cisco work, HP open view etc..
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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
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INFORMATION TO COLLECT Characterize the existing internetwork in terms of:
Its infrastructure
• Logical structure Logical topology = illustrates the architecture of the network
It can be flat or hierarchical, structured or unstructured, layered or not
Its also describes methods for connecting devices in a geometric shape – star , ring, bus, hub or mesh
Discuss further in chapter 5!!
Physical structure/components
Developing a modular block diagram – figure 3-2 page 69
Addressing and naming
Wiring and media
Architectural and environmental constraints
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GET A NETWORK MAP: INFORMATION TO
COLLECT A network map is the first thing to work on
This map should include
Geographic locations
WAN connections between sites Labeled with type/speed/protocols/media/service provider
Buildings and floors where equipment will be
Connections between buildings and floors Labeled with type/speed/protocols/media
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GET A NETWORK MAP: INFORMATION TO
COLLECT Location of connection points like routers and switches
Internet connections
Remote access points
A baseline will be needed as this will tell you where the network is today
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GET A NETWORK MAP-EXAMPLE
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Gigabit Ethernet
Eugene Ethernet20 users
Web/FTP server
Grants PassHQ
16 MbpsToken Ring
FEP (Front End Processor)
IBMMainframeT1
MedfordFast Ethernet
50 users
RoseburgFast Ethernet
30 usersFrame Relay
CIR = 56 KbpsDLCI = 5
Frame RelayCIR = 56 Kbps
DLCI = 4
Grants PassHQ
Fast Ethernet75 users
InternetT1
CHARACTERIZE ADDRESSING AND
NAMING IP addressing for major devices, client networks, server
networks, and so on
Any addressing oddities, such as discontiguous subnets?
Discontiguous subnet = is a subnet that is divided
Figure 3-3 pg 69 (text book)
Any strategies for addressing and naming?
For example, sites may be named using airport codes San Francisco = SFO, Oakland = OAK
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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
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WHAT SHOULD BE DOCUMENTED???
• To meet scalability and availability goals for new network design, it is important to understand the cabling and wiring of the existing network.
• documenting the existing cabling can help in designing for an enhancement and identify potential problems.
• It is also good to document the cable distance as this information is useful when selecting data link layer technologies based on distance restrictions
• Should document also the connections between buildings. Include the info on the number of pairs of wires and the type of wiring/wireless tech in use.
• should also indicate the distance between buildings- this help in selecting new cabling , i.e. upgrade from copper to fiber hence the distance between building can be much longer.
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TelecommunicationsWiring Closet
HorizontalWiring
Work-AreaWiring
Wallplate
Main Cross-Connect Room(or Main Distribution Frame)
Intermediate Cross-Connect Room(or Intermediate Distribution Frame)
Building A - Headquarters Building B
VerticalWiring
(BuildingBackbone)
CampusBackbone
CAMPUS NETWORK WIRING
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EXAMPLE: BUILDING WIRING
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ARCHITECTURAL CONSTRAINTS
Make sure the following are sufficient
Air conditioning
Heating
Ventilation
Power
Protection from electromagnetic interference
Doors that can lock
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ARCHITECTURAL CONSTRAINTS
Make sure there’s space for:
Cabling conduits
Patch panels
Equipment racks
Work areas for technicians installing and troubleshooting equipment
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CHECKING A SITE FOR A WIRELESS
INSTALLATION
Wireless site survey – to describe the process of analyzing a site to see if it will be appropriate for wireless transmission.
It starts with a draft WLAN design.
Decide on placement of the wireless access point.
the initial placement of the AP is based on an estimate of the signal loss that will occur between the AP and the users of the AP.
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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.
Spreading occurs in the diffraction process
[http://www.ask.com/question/difference-between-refraction-and-diffraction].
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CHECK THE HEALTH OF THE EXISTING
INTERNETWORK Performance
Availability
Bandwidth utilization
Accuracy
Efficiency
Response time
Status of major routers, switches, and firewalls
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0 1 2 3 4 5 6 7
17:10:00
17:07:00
17:04:00
17:01:00
16:58:00
16:55:00
16:52:00
16:49:00
16:46:00
16:43:00
16:40:00
Utilization
Tim
e
Network Utilization
NETWORK UTILIZATION IN MINUTE INTERVALS
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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
17:00:00
16:00:00
15:00:00
14:00:00
13:00:00
Utilization
Tim
e
Network Utilization
NETWORK UTILIZATION IN HOUR INTERVALS
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CHARACTERIZE PACKET SIZES
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Node A
Node B
Node C
Node D
Node A Node B Node C Node D
X
X
X
X
CHARACTERIZE RESPONSE TIME
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CHECK THE STATUS OF MAJOR ROUTERS,
SWITCHES, AND FIREWALLS show buffers
show environment
show interfaces
show memory
show processes
show running-config
show version
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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)
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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
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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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