CCDA Notes Strategic Network Design
This section introduces you to the Cisco Service-Oriented Network Architecture (SONA) framework for network design.In addition, you learn how to examine characteristics of an existing network, while determining design requirements. Finally, this section discusses Cisco’s top-down approach to network design.
Cisco Service-Oriented Network Architecture
Cisco recently updated its Architecture for Voice Video and Integrated Data (AVVID) design approach to the Intelligent Information Network (IIN). IIN is a complete architecture that is more all encompassing than AVVID.
The three phases of constructing an IIN are as follows:
- Integrated transport—Voice, data, and video are all converged onto a single transport.
- Integrated services—Services, such as VoIP or storage networking, rely on the underlying network transport mechanisms.
- Integrated applications—Applications (for example, Cisco IP Communicator) leverage services (for example, VoIP), which rely on the network transport.
The Cisco architectural approach to designing an IIN is their SONA framework. shows individual IIN components and how those components are categorized by SONA’s three layers: networked infrastructure layer, infrastructure services layer, and application layer.
SONA offers the following benefits to a network design:
Identifying Design Requirements
Cisco categorizes a network’s life cycle into six phases identified with the acronym PPDIOO. The components of PPDIOO are as follows:
- Prepare—This phase involves determining the network’s requirements, formulating a network strategy, and suggesting a conceptual architecture of the network.
- Plan—This phase compares the existing network with the proposed network to help identify tasks, responsibilities, milestones, and resources required to implement the design.
- Design—This phase clearly articulates the detailed design requirements.
- Implement—This phase integrates equipment into the existing network (without disrupting the existing network) to meet design requirements.
- Operate—This phase entails the day-to-day network operation, while responding to any issues that arise.
- Optimize—This phase gathers feedback from the Operate phase to potentially make adjustments in the existing network. Changes might be implemented to address ongoing network support issues.
PPDIOO’s life-cycle approach offers the following benefits:
- PPDIOO reduces total cost of ownership (TCO).
- PPDIOO improves network availability.
- PPDIOO allows business networks to quickly respond to changing needs.
- PPDIOO accelerates access to network applications and services.
Designing a network in conjunction with the PPDIOO approach involves three steps:
1. Identify customer requirements.
To identify customer requirements, obtain the following pieces of information:
- Network applications
- Network services
- Business goals
- Constraints imposed by the customer
- Technical goals
- Constraints imposed by technical limitations
2. Identify characteristics of the current network.
To identify characteristics of the current network, perform the following tasks:
- Collect existing network documentation (with the understanding that the documentation might be somewhat dated and unreliable), and interview organizational representatives to uncover information not available in the documentation.
- Conduct a network audit to identify information such as network traffic types, congestion points, and suboptimal routes.
- Supplement the information collected in the two previous tasks by performing a network traffic analysis with tools such as Cisco Discovery Protocol (CDP), Network Based Application Recognition (NBAR), NetFlow, Cisco CNS NetFlow Collection Engine, Open Source Cacti, Network General Sniffer, WildPackets EtherPeek and AiroPeek, SolarWinds Orion, Wireshark, and Remote Monitoring (RMON) probes.
3. Design the network topology.
Using information collected in Steps 1 and 2, you are ready to begin your network design. Although designing a network can be a daunting task, Cisco’s recommended top-down design approach assists the designer by breaking the design process into smaller and more manageable steps. The term top-down refers to beginning at the top of the OSI reference model (that is, the application layer) and working your way down through the underlying layers, as shown
Using a top-down design strategy as opposed to a bottom-up design strategy (that is, where the design begins at the physical layer of the OSI model and works its way up) provides the following benefits:
- Does a better job of including specific customer requirements
- Offers a more clearly articulated “big picture” of the desired network for both the customer and the designer
- Lays the foundation for a network that not only meets existing design requirements but provides for scalability to meet future network enhancements
When using the OSI reference model in the top-down design approach, the designer should determine what design decisions, if any, are required for each of the seven layers. For example, when considering the application layer, the designer might determine that voice applications such as the Cisco IP Contact Center and the Cisco Unity converged messaging system are applications needed for the design.
Network layer design decisions might include the selection of a routing protocol (for example, Enhanced Interior Gateway Routing Protocol [EIGRP] or Open Shortest Path First Protocol [OSPF]). Also, when analyzing the network layer, the designer might need to determine an appropriate IP addressing scheme for the network (for example, the use of private versus public IP addresses and subnet masks to be used) to provide for future network scalability.
Physical layer and data link layer design decisions might involve the selection of LAN/WAN technologies (for example, Gigabit Ethernet, Fast Ethernet, Frame Relay, ATM, or PPP) to provide for media transport.
With the multitude of design decisions required in larger networks, network designers often benefit from network design tools such as the following:
- Network modeling tools—Generate suggested configurations based on input information, which can then be further customized (for example, adding redundancy or support for additional sites)
- Strategic analysis tools—Enable a network designer to experiment with various “what-if” scenarios and observe resulting network effects
- Decision tables—Record design decisions based on network requirements
- Simulation and verification tools/services—Verify design decisions in a simulated environment to reduce the need to implement a pilot network
Even with the availability of simulation tools, some network designs still benefit from building a small prototype network to serve as a proof of concept. Such prototype networks are commonly known as pilot networks.