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Exam Essentials

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because layer-2 switches only break up collision domains and, by default, all
switches make up one large broadcast domain. I also described trunked
VLANs across a Fast Ethernet link.

Trunking is a crucial technology to understand well when you're dealing

with a network with multiple switches running several VLANs. I also talked
at length about VLAN Trunk Protocol (VTP), which really has nothing to do
with trunking. You learned that it does send VLAN information down a
trunked link, but that the trunk configuration in itself is not part of VTP.

Exam Essentials

Understand the term "frame tagging." Frame tagging refers to VLAN
identification; this is what switches use to keep track of all those frames
as they're traversing a switch fabric. It's how switches identify which
frames belong to which VLANs.

Understand the ISL VLAN identification method. Inter-Switch Link
(ISL) is a way of explicitly tagging VLAN information onto an Ethernet
frame. This tagging information allows VLANs to be multiplexed over a
trunk link through an external encapsulation method, which allows the
switch to identify the VLAN membership of a frame over the link. ISL is
a Cisco-proprietary frame-tagging method that can only be used with
Cisco switches.

Understand the 802.1Q VLAN identification method. A nonpropri-
etary IEEE method of frame tagging. If you're trunking between a Cisco
switched link and a different brand of switch, you have to use 802.1Q for
the trunk to work.

Remember the benefits of VLANs.

There are several benefits of

VLANs:

The VLAN can group several broadcast domains into multiple
logical subnets.

Network adds, moves, and changes are achieved by configuring a
port into the appropriate VLAN.

A group of users needing high security can be put into a VLAN so
that no users outside of the VLAN can communicate with them.

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