The Core Layer :
The core layer provides an optimized and reliable transport structure by forwarding traffic at very high speeds. In other words, the core layer switches packets as fast as possible. Devices at the core layer should not be burdened with any processes that stand in the way of switching packets at top speed. This includes the following:
Access-list checking
Data encryption
Address translation
The Distribution Layer :
The distribution layer is located between the access and core layers and helps differentiate the core from the rest of the network. The purpose of this layer is to provide boundary definition using access lists and other filters to limit what gets into the core. Therefore, this layer defines policy for the network. A policy is an approach to handling certain kinds of traffic, including the following:
Routing updates
Route summaries
VLAN traffic
Address aggregation
Use these policies to secure networks and to preserve resources by preventing unnecessary traffic.
If a network has two or more routing protocols, such as Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP), information between the different routing domains is shared, or redistributed, at the distribution layer.
The Access Layer :
The access layer supplies traffic to the network and performs network entry control. End users access network resources by way of the access layer. Acting as the front door to a network, the access layer employs access lists designed to prevent unauthorized users from gaining entry. The access layer can also give remote sites access to the network by way of a wide-area technology, such as Frame Relay, ISDN, or leased lines.
HTH,
Thanks
Raj
