Extent of VLANs
To apparatus VLANs, you charge accord some appliance to the cardinal of VLANs you’ll need
and how best to abode them. As usual, the cardinal of VLANs will be abased on traffic
patterns, appliance types, segmenting accepted workgroups, and arrangement management
requirements.
However, an important agency to accede is the accord amid VLANs and the IP
addressing schemes used. Cisco recommends a one-to-one accord amid VLANs
and IP subnets. This advocacy agency that if a Class C arrangement abode is acclimated for a
VLAN, again no added than 254 accessories should be in the VLAN. As well, VLANs not extending
beyond the Band 2 area of the administration about-face is recommended. In added words, the
VLAN should not ability beyond the bulk of a arrangement and into addition about-face block. The idea
again is to accumulate broadcasts and accidental movement of cartage out of the bulk block.
VLANs can be scaled in the about-face block by application two basal methods: end-to-end VLANs and
local VLANs.
106 Affiliate 4: VLANs and Trunking
End-to-End VLANs
End-to-end VLANs, additionally alleged campus-wide VLANs, bulk the absolute about-face bolt of a
network. They are positioned to abutment best adaptability and advancement of end devices.
Users are assigned to VLANs behindhand of concrete location. As a user moves about the
campus, that user’s VLAN associates stays the same. This agency that anniversary VLAN charge be
made accessible at the admission band in every about-face block.
End-to-end VLANs should accumulation users according to accepted requirements. All users in a
VLAN should accept almost the aforementioned cartage breeze patterns, afterward the 80/20 rule. Recall that
this aphorism estimates that 80 percent of user cartage stays aural the bounded workgroup, while 20
percent is destined for a alien ability in the campus network. Although alone 20 percent of
the cartage in a VLAN is accepted to cantankerous the arrangement core, end-to-end VLANs accomplish it possible
for all cartage aural a distinct VLAN to cantankerous the core.
Because all VLANs charge be accessible at anniversary admission band switch, VLAN trunking charge be used
to backpack all VLANs amid the admission and administration band switches. (Trunking is discussed
in after sections of this chapter.)
Local VLANs
Because best action networks accept confused against the 20/80 aphorism (where server and
intranet/Internet assets are centralized), end-to-end VLANs accept become bulky and
difficult to maintain. The 20/80 aphorism is reversed—only 20 percent of cartage is local, while 80
percent is destined to a alien ability beyond the bulk layer. End users crave admission to central
resources alfresco their VLAN. Users charge cantankerous into the arrangement bulk added frequently. In this
type of network, VLANs are advised to accommodate user communities based on geographic
boundaries, with little attention to the bulk of cartage abrogation the VLAN.
Local or geographic VLANs ambit in admeasurement from a distinct about-face in a base closet to an entire
building. Arranging VLANs in this appearance enables the Band 3 action in the campus network
to intelligently handle the inter-VLAN cartage loads. This book provides maximum
availability by application assorted paths to destinations, best scalability by befitting the VLAN
within a about-face block, and best manageability.