Lesson
9: Understanding Virtual LANs
What Is
a VLAN? | VLAN
Technologies
Virtual Trunk Protocol (VTP)
In addition to the ISL packet tagging method,
Cisco also created the Virtual Trunking Protocol, or VTP,
for dynamically configuring VLAN information across the network
regardless of media type (for example Fast Ethernet, ATM,
FDDI, and so on).
This VTP protocol is the software that makes ISL usable.
VTP enables VLAN communication from a centralized network
management platform, thus minimizing the amount of administration
that is required when adding or changing VLANs anywhere within
the network. VTP completely eliminates the need to administer
VLANs on a per-switch basis, an essential characteristic as
the number of a network’s switches and VLANs grows and
reaches a point where changes can no longer be reliably administered
on individual components. VTP allows for greater scalability
because it eliminates complex VLAN administration tasks across
every switch.
Conceptually, VTP works like this: When you add a new VLAN
to the network, let's say VLAN 1, VTP automatically goes out
and configures the trunk interfaces across the backbone for
that VLAN. This includes the mapping of ISL to LANE or to
802.1Q.
Adding a second VLAN is just as easy. VTP sends out new advertisements
and maps the VLAN across the appropriate interfaces. The important
thing to remember about this second VLAN, is that VTP keeps
track of the VLANs that already exist and eliminates any cross
configurations between these two, especially if this configuration
were to be done manually.
- Summary -
- VLANs enable logical (instead of
physical) groups of users on a switch
- VLANs address the needs for mobility and flexibility
- VLANs reduce administrative overhead, improve security,
and provide more efficient bandwidth utilization
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