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Chapter 3

VLANs

Switches advertise VTP management domain information as well as a

configuration revision number and all known VLANs with any specific
parameters.

You can configure switches to forward VTP information through trunk

ports but not accept information updates nor update their VTP database.
This is called VTP transparent mode.

You can set up a VTP domain with security by adding passwords, but

remember that every switch must be set up with the same password, which
may be difficult. However, if you are having problems with users adding
switches to your VTP domain, then a password can be used.

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. The information would be VLAN ID, 802.10 SAID
fields, or LANE information. Updates are sent out as revision numbers that
are notification +1. Anytime a switch sees a higher revision number, it knows
the information it receives is more current and will overwrite the current
database with the new one.

Do you remember the clear config all command we talked about in

Chapter 2? Well, guess what? It really doesn't "clear all" after all. It seems
that VTP has its own NVRAM, which mean that VTP information as well as
the revision number would still be present if you perform a clear config
all

and think that the configuration is gone. You can clear the revision num-

ber by power-cycling the switch.

VTP Modes of Operation

There are three different modes of operation within a VTP domain: server,
client, and transparent. Figure 3.4 shows the three VTP modes.

F I G U R E 3 . 4

VTP modes

Client

Transparent

Server

Server configuration: Saved in NVRAM

Transparent configuration: Saved in NVRAM

Client configuration: Not saved in NVRAM

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