What is VTP?
VTP allows a network manager to configure a switch so that it will propagate VLAN configurations to other switches in the network.
VTP only learns about normal-range VLANs (VLAN IDs 1 to 1005). Extended-range VLANs (IDs greater than 1005) are not supported by VTP.
VTP Domain-Consists of one or more interconnected switches. All switches in a domain share VLAN configuration details using VTP advertisements. A router or Layer 3 switch defines the boundary of each domain.
VTP Advertisements-VTP uses a hierarchy of advertisements to distribute and synchronize VLAN configurations across the network.
VTP Modes- A switch can be configured in one of three modes: server, client, or transparent.
VTP Server-VTP servers advertise the VTP domain VLAN information to other VTP-enabled switches in the same VTP domain. VTP servers store the VLAN information for the entire domain in NVRAM. The server is where VLANs can be created, deleted, or renamed for the domain.
VTP Client-VTP clients function the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client. A VTP client only stores the VLAN information for the entire domain while the switch is on. A switch reset deletes the VLAN information. You must configure VTP client mode on a switch.
VTP Transparent-Transparent switches forward VTP advertisements to VTP clients and VTP servers. Transparent switches do not participate in VTP. VLANs that are created, renamed, or deleted on transparent switches are local to that switch only.
VTP Pruning-VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even though receiving switches might discard them.
The benefit of VTP is that it automatically distributes and synchronizes domain and VLAN configurations across the network.
VTP Version-Displays the VTP version the switch is capable of running. By default, the switch implements version 1, but can be set to version 2.
Configuration Revision-Current configuration revision number on this switch. You will learn more about revisions numbers in this chapter.
Maximum VLANs Supported Locally-Maximum number of VLANs supported locally.
VTP Operating Mode-Can be server, client, or transparent.
VTP Domain Name-Name that identifies the administrative domain for the switch.
VTP Pruning Mode-Displays whether pruning is enabled or disabled.
VTP V2 Mode-Displays if VTP version 2 mode is enabled. VTP version 2 is disabled by default.
VTP Traps Generation-Displays whether VTP traps are sent to a network management station.
MD5 Digest-A 16-byte checksum of the VTP configuration.
Configuration Last Modified-Date and time of the last configuration modification. Displays the IP address of the switch that caused the configuration change to the database.
VTP Domains
VTP allows you to separate your network into smaller management domains to help reduce VLAN management.
A VTP domain consists of one switch or several interconnected switches sharing the same VTP domain name.
VTP Domain Name Propagation
For a VTP server or client switch to participate in a VTP-enabled network, it must be a part of the same domain. When switches are in different VTP domains, they do not exchange VTP messages.
VTP Frame Structure
VTP advertisements (or messages) distribute VTP domain name and VLAN configuration changes to VTP-enabled switches.
VTP Frame Encapsulation
A VTP frame consists of a header field and a message field. The VTP information is inserted into the data field of an Ethernet frame.
VTP frames contain the following fixed-length global domain information:
• VTP domain name
• Identity of the switch sending the message, and the time it was sent
• MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each VLAN
• Frame format: ISL or 802.1Q
VTP frames contain the following information for each configured VLAN:
• VLAN IDs (IEEE 802.1Q)
• VLAN name
• VLAN type
• VLAN state
• Additional VLAN configuration information specific to the VLAN type
VTP Revision Number
The configuration revision number is a 32-bit number that indicates the level of revision for a VTP frame. The default configuration number for a switch is zero.
The configuration revision number determines whether the configuration information received from another VTP-enabled switch is more recent than the version stored on the switch.
VTP Advertisements
Summary Advertisements
The summary advertisement contains the VTP domain name, the current revision number, and other VTP configuration details.
Request Advertisements
When a request advertisement is sent to a VTP server in the same VTP domain, the VTP server responds by sending a summary advertisement and then a subset advertisement.
Request advertisements are sent if:
• The VTP domain name has been changed
• The switch receives a summary advertisement with a higher configuration revision number than its own
• A subset advertisement message is missed for some reason
• The switch has been reset
Server Mode
In server mode, you can create, modify, and delete VLANs for the entire VTP domain. VTP server mode is the default mode for a Cisco switch. VTP servers advertise their VLAN configurations to other switches in the same VTP domain and synchronize their VLAN configurations with other switches based on advertisements received over trunk links.
Client Mode
If a switch is in client mode, you cannot create, change, or delete VLANs. In addition, the VLAN configuration information that a VTP client switch receives from a VTP server switch is stored in a VLAN database, not in NVRAM.
Transparent Mode
Switches configured in transparent mode forward VTP advertisements that they receive on trunk ports to other switches in the network.
VTP pruning
VTP pruning prevents unnecessary flooding of broadcast information from one VLAN across all trunks in a VTP domain. VTP pruning permits switches to negotiate which VLANs are assigned to ports at the other end of a trunk and, hence, prune the VLANs that are not assigned to ports on the remote switch.
