Local-Area Networks and LAN Switching - CCIE Routing and Switching Exam Certification Guide - page 155

Example 4-15 IEEE 802.1q Configuration Example (Continued)
!
interface fastethernet 1/1.3
encapsulation dot1q 30
ip address 192.168.3.1 255.255.255.0
On Catalyst, use the set trunk command. Because ISL is the default, the dot1q keyword is
necessary.
set trunk mod/port [on | desirable | auto | negotiate] dot1q
VLAN Trunk Protocol (VTP)
VTP is a Cisco proprietary protocol that distributes VLAN information among Catalyst switches.
VTP uses ISL or 802.1q encapsulated links to communicate. VTP's purpose is to ease the
administrative burden of managing VLANs, by managing the addition, deletion, and renaming
of VLANs.
With VTP, a VTP domain is created for all Catalyst switches that are to be in an administrative
domain. VTP operates through VTP messages (multicast messages) that are sent to a particular
MAC address (01-00-0C-CC-CC-CC). VTP advertisements only travel through trunk ports and
are carried only through VLAN 1.
VTP Switch Modes
Catalyst switches can be configured for one of three different VTP modes. The configuration
command is as follows:
set vtp mode [server | client | transparent]
The VTP server maintains a full list of all VLANs within the VTP domain. Information is stored
in NVRAM. The server can add, delete, and rename VLANs. The VTP client also maintains a
full list of all VLANs. However, it does not store in NVRAM. The client cannot add, delete, or
rename VLANs. Any changes made must be received from a VTP server advertisement. The
VTP transparent does not participate in VTP. However, it does pass on a VTP advertisement.
VLAN, as defined, is only local to the switch and is stored in NVRAM.
VTP Pruning
A major feature of VTP is VTP pruning, which limits the distribution of broadcasts throughout
the VTP domain. As shown in Figure 4-33, a VTP domain has VLANs 1, 2, and 3. If switch S3
does not have users in VLAN 1, no broadcasts are sent to switch S3.