What are two important guidelines to follow when implementing VTP?

What are two important guidelines to follow when implementing VTP? (Choose 2)

A.
CDP must be enabled on all switches in the VTP management domain

B.
Enabling VTP pruning on a server will enable the feature for the entire management domain

C.
All switches in the VTP domain must run the same version of VTP

D.
Use of the VTP muti-domain feature should be restricted to migration and temporary implementation.

E.
When using secure mode VTP, only configure management domain passwords on VTP servers.

Explanation:
VTP has 3 protocol versions Version 1, 2, & 3. VTP Version 3 incorporates many changes from VTP V1 and V2.
VTP Messages in Detail
VTP packets are sent in either Inter-Switch Link (ISL) frames or in IEEE 802.1Q (dot1q) frames. These packets are sent to the destination MAC address 01-00-0C-CC-CC-CC with a logical link control (LLC) code of Subnetwork Access Protocol (SNAP) (AAAA) and a type of 2003 (in the SNAP header). This is the format of a VTP packet that is encapsulated in ISL frames:

Of course, you can have a VTP packet inside 802.1Q frames. In that case, the ISL header and cyclic redundancy check (CRC) is replaced by dot1q tagging.
Summary Advertisements
By default, Catalyst switches issue summary advertisements in five-minute increments. Summary advertisements inform adjacent Catalysts of the current VTP domain name and the configuration revision number.
When the switch receives a summary advertisement packet, the switch compares the VTP domain name to its own VTP domain name. If the name is different, the switch simply ignores the packet. If the name is the same, the switch then compares the configuration revision to its own revision. If its own configuration revision is higher or equal, the packet is ignored. If it is lower, an advertisement request is sent.

This list clarifies what the fields means in the summary advertisement packet:
The Followers field indicates that this packet is followed by a Subset Advertisement packet. The Updater Identity is the IP address of the switch that is the last to have incremented the configuration revision.
The Update Timestamp is the date and time of the last increment of the configuration revision. Message Digest 5 (MD5) carries the VTP password, if MD5 is configured and used to authenticate the validation of a VTP update.
Subset Advertisements
When you add, delete, or change a VLAN in a Catalyst, the server Catalyst where the changes are made increments the configuration revision and issues a summary advertisement. One or several subset advertisements follow the summary advertisement. A subset advertisement contains a list of VLAN information. If there are several VLANs, more than one subset advertisement can be required in order to advertise all the VLANs.

VTP Pruning
VTP ensures that all switches in the VTP domain are aware of all VLANs. However, there are occasions when VTP can create unnecessary traffic. All unknown unicasts and broadcasts in a VLAN are flooded over the entire VLAN. All switches in the network receive all broadcasts, even in situations in which few users are connected in that VLAN. VTP pruning is a feature that you use in order to eliminate or prune this unnecessary traffic.
http://www.cisco.com/warp/public/473/21.html#vtp_pruning VLAN Pruning
VTP can prune unneeded VLANs from trunk links. VTP maintains a map of VLANs and switches, enabling traffic to be directed only to those switches known to have ports on the intended VLAN.
This enables more efficient use of trunk bandwidth.
Each switch will advertise which VLAN’s it has active to neighboring switches. The neighboring switches will then “prune” VLAN’s that are not active across that trunk, thus saving bandwidth. If a VLAN is then added to one of the switches, the switch will then re-advertise it’s active VLAN’s so that pruning can be updated by its neighbors. For this to work, VLAN pruning must be enabled on both ends of the trunk. It is easiest to enable VLAN pruning for an entire VTP management domain by simply enabling it on one of the VTP servers for that domain. To enable VLAN pruning for a VTP domain, enter the following command on a VTP server for that domain…
VTP_Server_Sw1(config)# vtp pruning
This will then propagate to all switches in the vtp domain.

Configure VLAN Pruning

Task
Command
Step 1
Enable VTP pruning in the management domain.
set vtp pruning enable
Step 2
(Optional) Make specific VLANs pruning-ineligible on the device.
(By default, VLANs 2-1000 are pruning-eligible.)
clear vtp pruneeligible vlan_range
Step 3
(Optional) Make specific VLANs pruning-eligible on the device.
set vtp pruneeligible vlan_range
Step 4
Verify the VTP pruning configuration.
show vtp domain
Step 5
Verify that the appropriate VLANs are being pruned on trunk ports.
show trunk

Topic 2, Volume C