1. Hierarchical Design

2. 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

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

4. 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

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

6. 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

7. 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

8. 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

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

10. 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

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

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

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

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

15. 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

16. 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

17. 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