The Core Layer

"Devices at this layer should not be burdened with access-list checking, data encryption, address translation, or any other process that stands in the way of switching packets at top speed."

The Distribution Layer

Policy-based routing  -  "A policy is an approach to handling certain kinds of traffic, including routing updates, route summaries, VLAN traffic, and address aggregation.  Administrators use policies to secure networks and tp preserve resources by preventing unnecessary traffic."

"We will configure them to use a combination of access lists, route summarization, distribute lists, route maps, and other rules to define how a router should deal with traffic and routing updates."

The Access Layer

"The access Layer feeds traffic into the network and performs network entry control.  As a network's "front door," the access layer employs access lists designed to prevent unauthroized users from gaining entry.  The access layer can also give remote sites access to the network...."

WAN Core Layer - 12000, 7500, 7200, and 7000 series routers

Distribution layer - 3600, 4500, and 4000 series routers

Access layer - 2600, 2500, 1700, and 1600 series routers

LAN Core Layer - Enterprise switches - Catalyst 4000, 5000, and 6000 series

All quotes from:

CCNP Cisco Networking Academy Program:  Semester Five Companion Guide Advanced Routing   Mark McGregor