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Chapter 6
Virtual LANs (VLANs)
Server The default for all Catalyst switches. You need at least one server
in your VTP domain to propagate VLAN information throughout the
domain. The switch must be in server mode to be able to create, add, or
delete VLANs in a VTP domain. Changing VTP information must also
be done in server mode, and any change made to a switch in server mode
will be advertised to the entire VTP domain.
Client In client mode, switches receives information from VTP servers,
and they also send and receives updates. But they can't make any changes.
Plus, none of the ports on a client switch can be added to a new VLAN
before the VTP server notifies the client switch of the new VLAN. Here's
a hint: If you want a switch to become a server, first make it a client so it
receives all the correct VLAN information, then change it to a server--
much easier!
Transparent Switches in transparent mode don't participate in the VTP
domain, but they will still forward VTP advertisements through any con-
figured trunk links. These switches can add and delete VLANs because
they keep their own database--one they do not share with other switches.
Transparent mode is really considered locally significant only.
When do I need to worry about VTP?
Whenever you have more than one switch and you have multiple VLANs.
If you have only one switch, then VTP is irrelevant. It also isn't important if
you are not configuring VLANs in your network. However, if you do have
multiple switches and use multiple VLANs, then you better configure your
VTP server and clients correctly!
When you first bring up your switched network, all switches are VTP servers
by default. Physically connect your switches, then configure the main switch
to be the VTP server and all others to be VTP clients. When you create VLANs
on the main VTP server, all switches will receive the VLAN database.
If you have an existing switched network and you want to add a new
switch, make sure to configure it as a VTP client before you install it. If
not, it's possible that this switch could send out a new VTP database to all
other switches, effectively wiping out all your VLANs!
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