CP3397 Network Design and Security Lecture 4 WAN design - Principles and practice.
Network Design Principles CP3397 Network Design and Security Lecture 2.
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Transcript of Network Design Principles CP3397 Network Design and Security Lecture 2.
Network Design Principles
CP3397 Network Design and SecurityLecture 2
Contents
Design goalsDesign choicesDesign approachesThe design processCapacity planning
Design goals
Good designs should: Deliver services requested by users Deliver acceptable throughput and response
times Be within budget and maximise cost efficiencies Be reliable Be expandable without major redesign Be manageable by maintenance and support
staff Be well documented
Design Choices
Balance of distributionLevel of transparencySecurityConnectivity technology
Design approaches
Two typical methods Traditional analytic design Building block approach
Both use a similar iterative approach
The traditional design process
A g r e e r e q u i r e m e n t s
I n f o r m a t i o n g a t h e r i n g
D e s i g n p r o c e s s
D e p l o y m e n t
C o m m i s s i o n i n g
M o d i f y
M e e t s c o n s t r a i n t s ?
Y e s
N o
Design Stages - Agree requirements
Engage end usersTranslate requirements Business objectives –> technical
specification
Phasing the requirements Right level of detail at each design
stage
Designing the requirements
Design Stages - Designing the requirements
Aim for completenessPrioritise with a hierarchical system such as
[M] - Mandatory [H] – Highly desirable [D] - Desirable [N] - Note
Design Stages - Assessing requirements
Consider all aspects E.g. support & maintenance, depreciation,
commissioning costs, project management fees, h/w & s/w upgrade costs, b/w/ costs, consultancy charges – over the lifetime of the network
Weighted matrix multipliers M=100, H=10, D=1, N=0 Produce scores and rank suppliers
Design Stages - Information gathering
Need to find details of user behaviour, application use and location information for example:
User: location, numbers, services used, typical access Sites: number, location, constraints on traffic (security, political
or cost) Servers and services: location, level of distribution WAN/backbone predicted link traffic Protocol support: bridged, routed or switched – Gateways
needed? Legacy support: equipment, protocols or services Specific availability needs? 24-hour/backup links etc Five-year plan – changes to population or business
requirements Budgetary constraints Greenfield or existing site
Information is refined and leads to a requirements database and capacity plan
Design Stages - Site constraints
Greenfield or Greenfield sites have no legacy constraints but… It is difficult to determine the real network loads and
stresses Needs more detail of application use and underlying
protocols Could use simulation to predict performance
Existing site Limited access Access to live network could be restricted but… Bottlenecks more obvious Can use traffic/network analysis tools
Design Stages - Planning
Uses information on Hosts, users, services, and their
internetworking needs
Iterative process of Conceptual design Analysis Refinement
Involving Brainstorming, design reviews, modelling
tools
Leading to final draft design
Design Stages - Design specification
Detailed document of the design Acts as a benchmark for design
changes Final design choices and changes
need justification and documenting Should include change history to aid
maintenance Used for the implementation
Design Stages - Implementation
Needs a project plan to include Phased introduction of new technology Educating the users (what to expect) Pilot installation (test for possible
problems) Acceptance testing (to prove
performance meets requirements) Deployment (provide support on going
live and provide fallback position)
Connectivity options
Technology choices LANs (Ethernet, Token ring, ATM) MANs (FDDI, SMDS, ATM, SONET/SDH) WANS (Frame relay, ATM, ISDN, X.25,
PDCs, Satellite) Wireless (802.11, Bluetooth, GPRS, GSM) Dial-up lines Serial links
Connectivity option determinants
Packet, cell or circuit switchingWired or wirelessDistancePerformanceBandwidthQuality of ServiceAvailability
Media and bandwidth choices
Capacity Planning - Outline
Concerned with User response times Application behaviour and performance
characteristics Network utilisation
Needed to Minimise downtime Maximise service to customers Minimise costs of procurement and
maintenance Avoid unscheduled maintenance or re-design Avoid costly upgrades and bad publicity
Capacity Planning - Stages
Form a discussion group (involve users etc.)Quantify user behaviourQuantify Application behaviourBaseline existing network Traffic profiles
Make traffic projectionsSummarize input data for design processAssess other data (environmental, location restrictions, deployment constraints etc)
Capacity Planning – Step 1
Form a discussion group (involve users etc.) Needs wide representation Users, network managers, application groups
To elicit What uses find acceptable and unacceptable Map of services and users and details of user behaviour
Quantify items using User and service sizing data Snapshots from data capture and network management
tools Traces of key services using protocol analysers Pilot network implementation
Capacity Planning – Step 2
Quantify user behaviour Need to know population and and
location of users Summary of major user groups Application use by user group Site location data (country, grid ref.,
town, postcode, telephone exchange) Planned changes
Capacity Planning – Step 3
Quantify Application behaviour Need to identify
Applications that could affect performance Location and performance of servers and clients Key constraints on performance (response times, buffer
sizes etc And define
Application behaviour under fault conditions (lost data) Addressing mechanisms( broad/multi/unicast) Packet characteristics (frame sizes and direction) Routable and non-routable services (IP, NETBIOS)
Undefined applications allow choice of distribution balance
Capacity Planning – Step 4
Baseline existing network Baselining – a behavioural profile of the network obtained
from Packet traces, transaction rates, event logs and stats Router ACLs, firewall rulebases Inventory of H/W and S/W revisions
Traffic profiles -Capture data for a stable working network with details of
B/w utilization by packet type and protocol Packet/frame size distribution Background error rates Collision rates
Various tools can be used Network and protocol analysers, SNMP data, RMON probes, OS
tools, traceroute, ping etc
Capacity Planning – Step 5
Make traffic projections using some, or all of: Hand calculation Commercial analytical tools to project
network utilisation Simulation tools (most detail)
Capacity Planning – Step 6
Summarize input data for design process Budget Database of sites, user populations, List of key applications and their behaviour Traffic matrix
Need to consider Static or dynamic bandwidth allocation Max. Delay and Max. hops between sites Resilience, Availability, degree of meshing Design constraints and trade-off
(e.g. delay v cost)
The building-block design process (an alternative)
NeedsAnalysis
Technologydesign
CostAssessment
Summary
Good design Is an iterative process of continuous
refinement Is logical and consistent Should deliver acceptable performance
and cost metrics (trade-off) Is more than choosing the technology!