Introducing Network Design Concepts

1. Introducing Network Design Concepts Designing and Supporting Computer Networks – Chapter 1

2. Objectives • Explain how a hierarchical network design creates a stable, reliable, scalable network • Explain what factors need to be considered when the Core Layer of a network is designed and implemented • Explain which factors need to be considered when the Distribution Layer of a network is designed and implemented • Explain which factors need to be considered when the Access Layer of a network is designed and implemented • Describe the benefits and security implications of creating server farms • Describe the considerations of an implementation of a wireless network design • Describe the factors that affect the implementation of VPNs, including how remote workers can be supported

3. Network Design requirements • Stay up all the time • Ease of management • Easy to modify to adapt to network growth and general business changes. • Fast troubleshooting • Fast recovery • Reliably deliver applications and provide reasonable response times • Be secure

4. Network Design goals • Scalability • Easily include new user groups and remote sites • Availability • single link failure should not impact entire network • Security • Must be designed into the network, not added on after the network is complete. • Manageability • Network staff must be able to manage and support the network

5. Hierarchical Network Design • It is used to group devices into three layers • Core Layer: connects Distribution Layer devices • Distribution Layer: interconnects smaller LANs • Access Layer: provides connections for hosts and end devices • Advantage of Hierarchical Network Design • More manageable network • Manages broadcasts

6. Cisco Enterprise Architecture • Subdivides the three-layer model into modular areas: • Enterprise campus • Server farm • Enterprise edge • Advantage • clearly defined boundaries between modules. • eases the design task by making each module independent. • provides scalability by allowing enterprises to add modules easily • enables the designer to add services and solutions without changing the underlying network design.

7. Network Design Methodologies • Steps in network design projects: • Identify the network requirements • Business goals • Technical requirements • Determine the scope of the network • Characterize the existing network • compare the functionality of the existing network with the defined goals of the new project. • Design the network topology and solutions • network applications and service requirements are identified, and then the network is designed to support them • impact of new network applications and services • new network addressing or routing protocol changes • new security measures • what will affect only a portion of the network

8. Designing the Network Core Layer • Core layer is the Network backbone • Provide high-speed connectivity. • Includes one or more links to the devices at the enterprise edge in order to support Internet, Virtual Private Networks (VPNs), extranet, and WAN access • Goals of the Core Layer • Prevent failures to provide 100% uptime • Human error (do not work directly on live network) • Dual power supplies and fans • A modular chassis-based design • Additional management modules • Power supplies and generators • Maximize throughput • Facilitate network growth • Technologies used at the Core Layer include: • Routers or multilayer switches • Redundancy and load balancing • Full or Partial Mesh topology • High-speed and aggregate links • Routing protocols that scale well and converge quickly, such as EIGRP and OSPF

9. Designing the Distribution Layer of a Network • Represents a routing boundary between the Access Layer and the Core Layer • Goals of the distribution layer • Filtering and managing traffic flow • Redundant links (STP) • Partial mesh topology. • Access control policies • Access control lists • Route summarization • One route in the routing table that represents many other routes, • Choose routing protocol that supports route summarization (EIGRP, RIPv2 and OSPF) • Isolating Core Layer from Access Layer failures • Routing between VLANs • trunks

10. Designing the Access Layer of a Network • Edge of the network where end devices connect. • Considerations include: • Physical location of equipment • Wired Ethernet (typically layer 2 switches) • Wireless access • Wiring closets • Termination point for infrastructure cabling within buildings or within floors of a building • Provides power to end devices such as IP phones and wireless Access Points • Converged networking • Data, Voice and Video • QoS, traffic segregation, and filtering. • Availability • Redundant components and failover strategies • Access layer management • increase in the number and types of devices connecting at the Access Layer and introduction of wireless access points into the LAN • Naming structures, VLAN architecture, Traffic patterns, Prioritization strategies • Security (physical security, securing access to devices and applications, worms and viruses, security policy) • Topology used is usually star topology • VLANs • logically independent IP subnet • Limit broadcast domains

11. Server Farms • Collection of servers located in a central facility to provide server need to organisations • Benefits • Defined entry and exit points for network traffic • Redundant, high-capacity links • Load balancing and failover • Lower cost of providing services • Provide high availability for network services and applications • DMZs • Protecting Server Farms Against Attack • Firewalls • LAN switch security features • Host-based and network-based intrusion detection and prevention systems • Load balancers • Network analysis and management devices

12. Wireless Network Design • Understand customer requirements for wireless LAN: • Roaming • Authentication • Services and applications • Encryption • Coverage and number of users • Network Design • Physical • Locations for mounting of access points • Access Point hardware, types of antennas, and the desired wireless feature sets. • Logical • Levels of access to different types of wireless users • Easy to use and secure

13. Designing the Enterprise Edge • Area of the network where the enterprise network connects to external networks. • Provide connectivity between the internal campus infrastructure and the Internet • Provide connectivity to remote WAN users and services • Design requirements to consider include • Cost of bandwidth • QoS • Security • Remote access • Interconnection options: • Traditional WAN technologies • Leased lines • Circuit-switched networks • Packet-switched networks, such as Frame Relay networks • Cell-switched networks such as Asynchronous Transfer Mode (ATM) • Newer WAN technologies • Digital Subscriber Line (DSL) • Metro Ethernet • Cable modem • Long-range wireless • Multiprotocol Label Switching (MPLS)

14. Integrating Remote sites into the network design • Employees who work offsite include • Remote workers • Mobile workers • Branch employees • Ways to provide redundant connectivity to remote sites • Virtual Private Networks • private network that uses a public network to connect remote sites or users together • uses virtual connections routed through the Internet from the company private network to the remote router or PC.

15. Summary • The four fundamental technical requirements of network design are scalability, availability, security and manageability. • Network projects involve identifying the requirements, characterizing the existing network, and designing the network topology and solutions. • Redundancy at the Core Layer keeps the network functioning even when a device or link fails. • Routing efficiency at the Distribution Layer isolates the Core from Access Layer failures. • Using VLANs and IP subnets is the most common way to segregate user groups and traffic within the Access Layer.