Configuring the VTP Mode
Next, you need to choose the VTP mode for the new switch. The three VTP modes of operation and their guidelines for use are as follows:
■ Server mode—Server mode can be used on any switch in a management domain, even if other server and client switches are in use. This mode provides some redundancy in case of a server failure in the domain. Each VTP management domain should have at least one server. The first server defined in a network also defines the management domain that will be used by future VTP servers and clients. Server mode is the default VTP mode and allows VLANs to be created and deleted.
NOTE Multiple VTP servers can coexist in a domain. This usually is recommended for redundancy. The servers do not elect a primary or secondary server; they all simply function as servers. If one server is configured with a new VLAN or VTP parameter, it advertises the changes to the rest of the domain. All other servers synchronize their VTP databases to this advertisement, just as any VTP client would.
■ Client mode—If other switches are in the management domain, you should configure a new switch for client mode operation. In this way, the switch is forced to learn any existing VTP information from a reliable existing server. After the switch has learned the current VTP information, you can reconfigure it for server mode if it will be used as a redundant server.
■ Transparent mode—This mode is used if a switch will not share VLAN information with any other switch in the network. VLANs still can be created, deleted, and modified on the transparent switch. However, they are not advertised to other neighboring switches. VTP advertisements received by a transparent switch, however, are forwarded to other switches on trunk links.
Keeping switches in transparent mode can eliminate the chance for duplicate, overlapping VLANs in a large network with many network administrators. For example, two administrators might configure VLANs on switches in their respective areas but use the same VLAN identification or VLAN number. Even though the two VLANs have different meanings and purposes, they could overlap if both administrators advertised them using VTP servers.
You can configure the VTP mode with the following sequence of global configuration commands:
Switch(config)# vtp mode {server I client I transparent}
Switch(config)# vtp password password
If the domain is operating in secure mode, a password also can be defined. The password can be configured only on VTP servers and clients. The password itself is not sent; instead, an MD5 digest or hash code is computed and sent in VTP advertisements (servers) and is used to validate received advertisements (clients). The password is a string of 1 to 32 characters (case-sensitive).
If secure VTP is implemented using passwords, begin by configuring a password on the VTP servers. The client switches retain the last-known VTP information but cannot process received advertisements until the same password is configured on them, too.
Continue reading here: VTP Pruning
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