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Topologies and IDS • Chapter 7 445

NOTE
You must have a functional intranet setup before attempting to create
an extranet.

EXAM WARNING

Be able to readily define an extranet. You must know the difference
between the Internet, intranet, and extranet.

VLANs

A VLAN can be thought of as the equivalent to a broadcast domain.

TEST DAY TIP
A broadcast domain consists of a group of nodes (computers) that
receive layer 2 broadcasts sent by other members of the same group.
Typically, broadcast domains are separated by creating additional net-
work segments or by adding a router.
Do not confuse broadcast domains with collision domains. Collision
domains refer specifically to Ethernet networks. The area of network
cabling between layer 2 devices is known as a collision domain. Layer 2
devices typically include switches that rely on the physical address
(Media Access Control [MAC] address) of computers to route traffic.

VLANs are a way to segment a network, as discussed above.When thinking of
a VLAN, think of taking a switch and physically cutting it into two or more pieces
with an axe. Special software features found in newer, more expensive switches,
allow administrators to physically split one physical switch into multiple logical
switches, thus creating multiple network segments that are completely separate
from one another.
The VLAN is thus a logical local area network that uses a basis other than a
physical location to map the computers that belong to each separate VLAN (e.g.,

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