ii. Distribution Layer
The distribution layer serves many important services for the
LAN. The primary function is to serve as an aggregation point for multiple
access layer switches in a given location or campus. In a network where
connectivity needs to traverse the LAN end-to-end, whether between different
access layer devices or from an access layer device to the WAN, the
distribution layer facilitates this connectivity.
Figure 5.7: distribution layer JKUAT LAN Campus
Scalability
In any network where multiple access layer devices exist at a
location to serve end-user connectivity, it becomes impractical to interconnect
each access switch as the access layer grows beyond two or three switches. The
distribution layer provides a logical point to summarize addressing and to
create a boundary for protocols and features necessary for the access layer
operation. Another benefit of the distribution layer boundary is that it
creates fault domains that serve to contain failures or network changes to
those parts of the network directly affected.
iii. Core Layer
In a large LAN environment there often arises a need to have
multiple distribution layer switches. One reason for this is that when access
layer switches are located in multiple geographically dispersed buildings, you
cansave costly fiber-optic runs between buildings by locating a distribution
layer switch in each of those buildings. As networks grow beyond three
distribution layers in a single location, organizations should use a core layer
to optimize the design. Another reason to use multiple distribution layer
switches is when the number of access layer switches connecting to a single
distribution layer exceeds the performance goals of the network designer. In a
modular and scalable design, you can collocate distribution layers for data
center, WAN connectivity, or Internet Edge services.
In environments where multiple distribution layer switches exist
in close proximity and where fiber optics provide the ability for high-speed
interconnect, a core layer reduces the network complexity, as shown in the
following two figures.
Figure 5.8: JKUAT LAN core layer
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