© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Applying a Methodology to Network Design Using the Top-Down Approach to Network Design

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Top-Down Design Practices Start your design here. Design down the OSI model.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Top-Down and Bottom-Up Approach Comparison Top-Down ApproachBottom-Up Approach Benefits Incorporates organizational requirements Gives the big picture to organization and designer Allows a quick response to a design request Facilitates design based on previous experience Disadvantages Incorporates organizational requirements Implements little or no notion of actual organizational requirements May result in inappropriate network design

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Top-Down Voice Design

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Creating a Network Decision Table Decide which network layer requires decisions. Gather possible options for a given situation. Create a table that includes possible options and given requirements. Match given requirements with specific properties of given options. Select the option with the most matches as the most appropriate one.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Selecting a Routing Protocol Options ParametersEIGRPOSPFBGP Required Network Parameters Size of Network (Small/Medium/Large/Very Large) Large Very LargeLarge Enterprise-Focused (Yes/No) Yes NoYes Use of VLSM (Yes/No) Yes Supports Cisco Routers (Yes/No) Yes Network Support Staff Knowledge (Good/Fair/Poor) GoodFairPoorGood

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Assessing the Scope of the Network Design Process Scope of DesignComments Entire networkAll branch office LANs upgraded to support Fast Ethernet technology Campus Redundant equipment and links Addition of wireless client mobility WANSolutions to overcome bottlenecks

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Assessing the Scope of the Network Design Process ApplicationDesigning voice transport NetworkDesigning routing, addressing Physical, data linkChoosing connection type

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Structured Design Principles

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Cisco SONA Offerings

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Network Design Tools

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Planning an Implementation If a design is composed of multiple complex components: –Implement each component separately; do not implement everything at once. Incremental implementation: –Reduces troubleshooting in case of failure –Reduces time needed to revert to previous state in case of failure

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Major Implementation Components Each step should contain the following information: Description Reference to design sections Detailed implementation guidelines Detailed roll-back guidelines in case of failure Estimated time for implementation

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Summary Implementation Plan Date, TimeDescription Implementation Details Complete Phase 304/02/2007Install campus hardwareSection Step 1Connect switchesSection Step 2Install routersSection Step 3Complete cablingSection Step 4Verify data link layerSection Phase 404/03/2007Configure campus hardwareSection Step 1Configure VLANsSection Step 2Configure IP addressingSection Step 3Configure routingSection Step 4Verify connectivitySection Phase 504/05/2007 Launch campus updates into production Section Step 1… Complete connections to existing network Section Step 2Verify connectivitySection

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Detailed Implementation Plan Section , Configure routing protocols in the WAN network module: Number of routers involved is 50. Use template from section 4.3.1, EIGRP details. Per router configuration: –Use passive-interface command on all nonbackbone LANs. (See section 4.2.3, EIGRP details.) –Use summarization according to the design. (See section 4.2.3, EIGRP details, and section 4.2.2, Addressing details.) Estimated time is 10 minutes per router. Roll-back procedure is not required.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Pilot vs. Prototype Networks The pilot or prototype network is used as proof of concept for the design: –A pilot network tests and verifies the design before the network is launched. –A prototype network tests and verifies a redesign in an isolated network before it is applied to the existing network. Results: –Success –Failure

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Example: Prototype Network

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Detailed Structure of a Design Document

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Summary Designing an enterprise network is a complex project. Top-down design facilitates the process by dividing it into smaller, more manageable steps. Decision tables facilitate the selection of the most appropriate option from many possibilities. In assessing the scope of a network design, determine whether the design is for a new network or is a modification of the entire network, a single segment or module, a set of LANs, a WAN, or a remote-access network. The output of the design should be a model of the complete system. To achieve this, the top-down approach is highly recommended.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v Summary (Cont.) When the design is complete, you are ready to document the implementation and migration in as much detail as possible. After a design is complete, you should verify it. You can test the design in an existing or live network (pilot) or in a prototype network that will not affect the existing network. A design document lists the design requirements, documents the existing network, documents the network design, identifies the proof-of-concept strategy, and details an implementation plan.

© 2007 Cisco Systems, Inc. All rights reserved.DESGN v