Cisco Hierarchical Model

There are three layers to the Cisco hierarchical model

1. The core (Backbone) layer provides optimal transport between sites.

2.The distribution layer provides policy-based connectivity.

3.The local-access layer provides workgroup/user access to the network.

 

Core Layer

Responsible for transporting large amounts of traffic reliably and quickly. Only purpose is to switch traffic as fast as possible (speed and latency are factors). Failure at the Core layer can affect every user.

 

Design specifications:

Don't Do at this layer

  • Don't use access lists, packet filtering, or VLAN Routing.
  • Don't support workgroup access here.
  • Don't expand (more devices) upgrade instead (faster devices)

 

Do at this layer

  • Design for high reliability (FDDI, Fast Ethernet with redundant links, or ATM).
  • Design for speed and low latency.
  • Use routing protocols with low convergence times.

 

 

Distribution Layer

Also called workgroup layer, is the communication point between access and core layers. Primary function, routing, filtering, WAN access, and determine how packets can access the Core layer if necessary. Determine fastest/best path and send request to Core layer. Core layer will then quickly transport the request to the correct service. Place to implement network policies.

 

Network Policies

  • Access lists, packet filtering, queuing
  • Security and network policies such as address translation and firewalling.
  • Redistribution between routing protocols including static routing.
  • Routing between VLANs and other workgroup support functions.
  • Definition of broadcast and multi-cast domains.

 

Access Layer

  • Controls user and workgroup access to internetwork resources.
  • Also called desktop layer. -The resources most user need will be available locally.
  • Distribution layer handles traffic for remote services.
  • Continued access control and policies.
  • Creation of separate collision domains (segmentation)
  • Workgroup connectivity in Distribution layer
  • Technologies such as DDR and Ethernet switching are seen in the Access layer
  • Static routing is here.