Hierarchical Design

Objectives Describe the benefits of using a hierarchical design model Identify the three layers that make up the hierarchical model Describe the functions typically performed at each layer

Three-Layer Model Components Core Campus Backbone Distribution Building Backbone Access Remote Workgroups Local Workgroups

Core-Layer Functions Optimized transport between remote sites Site A Site C Site B Optimized transport between remote sites Redundant paths Load sharing Rapid convergence Efficient use of bandwidth

Distribution-Layer Functions Campus Backbone Building Backbone Policy-based connectivity Control access to services Define path metrics Control network advertisements

Access-Layer Functions Building Backbone Connect workgroups to backbones Provide logical segmentation Group users with common interests Isolate broadcast traffic from the workgroup Distribute services between multiple CPUs

Hierarchical model divide nodes into levels; intra-level nodes talk to each other mostly; level functional independent inter-level communications is summarised adv. : better control, scalability & modularity control - grouping ease network management scalability - traffic contained within region modularity -same cost/method for adding node adding new nodes won’t disturb other levels ; network can grow smoothly & uniformly

Hierarchical model (Cont.) disadv. : address administration overhead recommended for enterprise networks many hierarchical models exist Cisco network model core level :high speed transport for internetwork distribution level :implement management policy access level :connectivity to desktop PCs

Benefits of a Hierarchical Design Model Scalability Ease of implementation Ease of troubleshooting Predictability Protocol Support Manageability

Flat model every node is equal and talks to each other advantage is plug-and-play for small network disadvantage is lack of scalability due to excessive communications and CPU overhead may require a major upgrade at certain point if network continues to grow generally not recommended as an enterprise network architecture

One-Layer Design-Distributed Core WAN Site A Site C Site B

One-Layer Design-Hub and Spoke Central Site Core WAN Remote Site

Two-Layer Design SiteB Core WAN Site C Campus Backbone Site A Building A1 Building A2

Redundant Two-Layer Hierarchy Data Center Remote Site 1 Use for cost-effective LAN redundancy

Guidelines for effective deployment Do not mesh the network within a layer Do not place end stations on backbones Keep 80% of the traffic local to the workgroup Use network features at the appropriate layer

Logical topology flat (L2 protocol) hierarchical (L3 protocol) logical topology may differ from physical choices depend on network protocols used : flat (L2 protocol) hierarchical (L3 protocol) flat logical structure : based on low cost switches; bridges are out plug-and-play; no address administration not scaleable; need to contain broadcast

Logical structure (Cont.) hierarchical logical structure : based on expensive routers or L3 switches need address administration scaleable; better control and manageability several logical structures can co-exist in a multiple protocol network