Chapter 6: VLANs and Trunking 99
Section 6-4
a. Specify a VTP domain name:
(privileged) vlan database
(vlan_database) vtp domain name
OR
(global) vtp domain name
By default VTP is in server mode, which is an operational mode that enables you
to manage VLANs on the local switch’s database and use the information in the
database to synchronize with other switches. To configure VTP for operation,
you must specify a name. After you enable trunking, this name propagates to
switches that have not been configured with a name. If you choose to configure
names on your switches, however, remember that VTP names are case-sensitive
and must match exactly. Switches that have different VTP names will not
exchange VLAN information.
Note The global configuration command vtp domain is not supported on all switches
that run the IOS.
Note VTP names are used only in the context of synchronizing VTP databases. VTP
domain names do not separate broadcast domains. If VLAN 20 exists on two switches
trunked together with different VTP domain names, VLAN 20 is still the same broadcast
domain!
b. Enable the trunk:
(global) interface type mod/port
(interface) switchport mode dynamic [auto | desirable]
(interface) switchport mode trunk
(interface) switchport nonegotiate
VTP information is passed only across trunk links. If you do not enable a trunk,
VLAN information is not exchanged between the switches. See section “6-3:
Trunking” for more details on trunking.
Note Some IOS switches do not support DTP. For these switches, the only command
that you can use to configure trunking is switchport mode trunk, which essentially turns
trunking on.
Setting VTP Passwords
By default, there are no passwords in VTP informational updates, and any switch that has
no VTP domain name will join the VTP domain when trunking is enabled. Also any
switch that has the same VTP domain name configured will join and exchange VTP infor-
mation. This could enable an unwanted switch in your network to manage the VLAN
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