CCNA Cisco Certified Network Associate Study Guide - FTP Server

36 Chapter 1 � Internetworking
The Access Layer
The distribution layer must determine the fastest way that network service
requests are handled; for example, how a file request is forwarded to a
server. After the distribution layer determines the best path, it forwards the
request to the core layer. The core layer then quickly transports the request
to the correct service.
The distribution layer is the place to implement policies for the network.
Here you can exercise considerable flexibility in defining network operation.
There are several items that generally should be done at the distribution
layer. They include the following:
� Implementation of tools such as access lists, of packet filtering, and of
queuing
� Implementation of security and network policies, including address
translation and firewalls
� Redistribution between routing protocols, including static routing
� Routing between VLANs and other workgroup support functions
� Definitions of broadcast and multicast domains
Things to avoid at the distribution layer are limited to those functions that
exclusively belong to one of the other layers.
The access layer controls user and workgroup access to internetwork
resources. The access layer is sometimes referred to as the desktop layer. The
network resources most users need will be available locally. The distribution
layer handles any traffic for remote services. The following are some of the
functions to be included at the access layer:
� Continued (from distribution layer) access control and policies
� Creation of separate collision domains (segmentation)
� Workgroup connectivity into the distribution layer
Technologies such as DDR and Ethernet switching are frequently seen in
the access layer. Static routing (instead of dynamic routing protocols) is seen
here as well.
As already noted, three separate levels does not imply three separate routers.
It could be fewer, or it could be more. Remember, this is a layered approach.