Cisco Hierarchical Network Model RD-CSY /101

Outline Network Design and Planning for Enterprise networks Cisco 3 Layer hierarchical Model ◦ Core, Distribution and Access Layers ◦ Hub and spoke designs ◦ Mesh topologies RD-CSY /102

Internetworking Typical Enterprise Network  Internetworking is the communication between two or more networks ◦ Requires many protocols and features to  permit scalability  manageability without constant manual intervention  Large internetworks can consist of the three distinct components: 1. Campus networks, which consist of locally connected users in a building or group of buildings 2. Wide-area networks (WANs), which connect campuses together 3. Remote connections, which link branch offices and single users (mobile users and/or telecommuters) to a local campus or the Internet 3RD-CSY3021

High Level view of Enterprise Network RD-CSY /104

Why reference model for network design Large networks can be extremely complicated, ◦ with multiple protocols  IPv4, IPv6, IPX, Appletalk ◦ detailed configurations, and ◦ diverse technologies  Frame Relay, FDDI, ATM, Ethernet, Token Ring Hierarchy helps us summarize a complex collection of details into an understandable model Hierarchy, when used properly, makes network more predictable The Cisco hierarchical model can help you design, implement, and maintain a scalable, reliable, cost-effective hierarchical internetwork RD-CSY /105

Campus Networks Campus Network  A campus is a building or group of buildings all connected into one enterprise network that consists of many local area networks (LANs). ◦ A large campus with groups of buildings can also use WAN technology to connect the buildings  Campus network generally optimized for the fastest functional architecture that runs on existing physical wire.  Scalable to requirements of emerging applications 6RD-CSY3021

Why Use a Hierarchical Model? Reduces workload on network devices ◦ Avoids devices having to communicate with too many other devices (reduces “CPU adjacencies”) Constrains broadcast domains Enhances simplicity and understanding Facilitates changes Facilitates scaling to a larger size

Cisco’s Hierarchical Design Model Like OSI 7 layer model, Cisco hierarchical model is a three layered model. The layers from below are: ◦ Layer 1: Access ◦ Layer 2: Distribution ◦ Layer 3: Core A core layer of high-end routers and switches that are optimized for availability and speed A distribution layer of routers and switches that implement policies and segment traffic An access layer that connects users via hubs, switches, and other devices

Hierarchical Network Design Enterprise WAN Backbone Campus ACampus B Campus C Building C-1Building C-2 Campus C Backbone Core Layer Distribution Layer Access Layer

Flat Versus Hierarchy Flat Loop Topology Headquarter in Bedford Grimsby Branch Office Ashford Branch Office Kelmarsh Branch Office Headquarters in Bedford Ashford Branch Office Kelmarsh Branch Office Grimsby Branch Office Whitby Branch Office Hierarchical Redundant Topology

Mesh Designs Full and partial mesh designs are used in network design to provide redundancy or high availability Partial-Mesh TopologyFull-Mesh Topology

A Partial-Mesh Hierarchical Design Headquarters (Core Layer) Branch Offices (Access Layer) Regional Offices (Distribution Layer)

A Hub-and-Spoke Hierarchical Topology Single hub node ◦ Common in enterprise networks ◦ Main location and satellite sites ◦ Simple design and trivial routing Problems ◦ Single point of failure ◦ Bandwidth limitations ◦ High delay between sites ◦ Costs to backhaul to hub Corporate Headquarters Branch Office Home Office

14 Simple Alternatives to Hub-and-Spoke Dual hub-and-spoke ◦ Higher reliability ◦ Higher cost ◦ Good building block Levels of hierarchy ◦ Reduce backhaul cost ◦ Aggregate the bandwidth ◦ Shorter site-to-site delay …

Avoid Chains and Backdoors Core Layer Distribution Layer Access Layer Chain Backdoor

How Do You Know When You Have a Good Design? When you already know how to add a new building, floor, WAN link, remote site, e- commerce service, and so on When new additions cause only local change, to the directly-connected devices When your network can double or triple in size without major design changes When troubleshooting is easy because there are no complex protocol interactions to wrap your brain around

Cisco’s SAFE Security Reference Architecture

Enterprise Composite Network Model 18RD-CSY3021

Grouping Devices into Networks and Hierarchical Addressing Devices are grouped into sub-networks Based on geographical location Based on Functionality Departments Communication requirements RD-CSY /1019

Network Designs: breaking into sub-networks Given a network requirement, find the optimum number of sub networks in the larger inter-network. ◦ Count on the basis of  Departments  Geographical locations.. Determine the total number of hosts in a network, accounting for present and future requirements Hosts include ◦ PCs, printers, servers, special devices RD-CSY /1020

Campus Topology Design Use a hierarchical, modular approach Minimize the size of bandwidth domains Minimize the size of broadcast domains Provide redundancy ◦ Mirrored servers ◦ Multiple ways for workstations to reach a router for off-net communications

Next Week Revisit IP Addressing Subnetting Class B subnetting RD-CSY /1022