Page 379

VLAN Trunk Protocol (VTP)

333

Very cool, but before you can get VTP to manage your VLANs across the

network, you have to create a VTP server. All servers that need to share VLAN
information must use the same domain name, and a switch can only be in one
domain at a time. So, this means that a switch can only share VTP domain in-
formation with other switches if they're configured into the same VTP domain.
You can use a VTP domain if you have more than one switch connected in a
network, but if you've got all your switches in only one VLAN, you don't need
to use VTP. VTP information is sent between switches via a trunk port.

Switches advertise VTP-management domain information, as well as a

configuration revision number and all known VLANs with any specific
parameters. And there's also something called

VTP transparent mode

. In

it, you can configure switches to forward VTP information through trunk
ports, but not to accept information updates or update their VTP databases.

If you find yourself having problems with users adding switches to your

VTP domain, you can include passwords, but don't forget--every switch
must be set up with the same password, and this can be difficult.

Switches detect the additional VLANs within a VTP advertisement and

then prepare to receive information on their trunk ports with the newly
defined VLAN in tow. This information would be either VLAN ID, 802.10
SAID fields, or LANE information. Updates are sent out as revision numbers
that are the notification plus 1. Any time a switch sees a higher revision num-
ber, it knows the information that it's receiving is more current, and it will
overwrite the current database with that new information.

VTP Modes of Operation

There are three different modes of operation within a VTP domain. Figure 6.6
shows you all three:

F I G U R E 6 . 6

VTP modes

Client

Transparent

Server

Server configuration: Saved in NVRAM

Transparent configuration: Saved in NVRAM

Client configuration: Not saved in NVRAM

www.sybex.com