VLANs, Trunks, and VTP

VLANs, Trunks,
and VTP
THE CCNP EXAM TOPICS COVERED IN THIS
CHAPTER INCLUDE THE FOLLOWING:


Describe LAN segmentation with VLANs.


Ensure broadcast domain integrity by establishing VLANs.


Configure access ports for static membership of single and
multiple VLANs.


Describe the different Trunking Protocols.


Configure ports as 802.1Q trunks and verify their operation.


Configure ports as ISL trunks and verify their operation.


Understand the operation of VTPv1 and VTPv2, including the
functions of domains, modes, advertisements, and pruning.


Configure switches in VTP domains in server, client, and
transparent modes.


Understand local VLANs and end-to-end VLANs, and
determine which to use.


Design VLAN configurations with VTP for operation in a
specific scenario.


Understand managed VLAN services.


Know the features and functionality of 802.1Q Tunneling
(802.1QinQ) in service provider networks.


Configure auxiliary VLANs with IP technology.

You likely already know that a LAN is a group of stations that use
broadcast frames to share common services. Most legacy protocols
use broadcasts to carry out simple administrative functions
such as finding a server, advertising their services, and even acquiring naming and addressing
information. These days, we can go much further using a virtual local area network (VLAN).
A VLAN is a logical grouping of network users and resources connected to administratively
defined ports on a layer 2 switch. By creating these administrative groupings, you are able to create
smaller broadcast domains within a switch by assigning different ports in the switch to different subnetworks.
A VLAN is treated as its own subnet or broadcast domain. This means that when frames
are broadcast, they are switched between ports only within the same VLAN.
By using VLANs, you’re no longer confined to creating workgroups based on physical locations.
VLANs can be organized by location, function, department, or even the application or protocol
used, regardless of where the resources or users are located. VLANs can be created locally on a single
switch, or they can be extended across many switches in a LAN, using special trunk protocols to
carry the additional VLAN header information. This technique is called
frame tagging
, and it uses
special identification methods that either encapsulate a frame or insert a new field in a frame, to identify
it as belonging to a particular VLAN as it traverses a switched internetwork fabric.
One of the real problems facing network administrators managing large switched networks
is that of consistency. With VLAN numbers and names requiring unique configuration, it is easy
to lose control of the process, resulting in conflicting information about the same VLAN.
VTP—the VLAN Trunking Protocol—was developed to deal precisely with this problem. By
creating a process where one switch can act as a server, updating other switches in the same
domain, consistency of VLAN description can easily be achieved.