1.4 Collapsed core vs Three tier

The following layers may or may not be on separate devices.

1. The Core Layer-
   • Literally the core of the network- If this has issues, everyone has issues.
   • Dont do these-
     1. Never do anything to slow down traffic, no ACL's, no routing, don't implement packet filtering
     2. Don't support work group access
     3. Avoid expanding the core(adding more routers)- If performance is an issue upgrade
   • Do these
     1. Design for high availability
     2. Design with speed in mind
     3. Select routing protocols with low convergence times
2. Distribution layer-
   • Sometimes referred to as the workgroup layer- Communicates between the access layer and the core.
   • Key things handled at the distribution layer
     1. Routing
     2. Implementing tools(access lists), packet filtering and queuing
     3. Implementing security and network policies, including address translation and firewalls
     4. Redistributing between routing protocols, including static
     5. Routing between VLAN's and other workgroup support functions
     6. Defining broadcast and multicast domains
3. Access Layer-
   • Controls user and workstation access- sometimes refered to as the desktop layer
   • Key functions
     1. Continued(From Distribution layer) use of access control and policies
     2. Creation of separate collision domains.
     3. Work group connectivity into the distribution layer
     4. Device connectivity
     5. Resilience and security services
     6. Advanced technology capabilities(Voice/Video)