VTP: Cisco VLAN TRUNKING Protocol
(VTP: Cisco VLAN Relay Agreement)
The VLAN Trunk Protocol (VTP) is the Cisco Layer 2 information transfer protocol, which mainly controls the addition, deletion, and rename of VLANS within the network. VTP reduces the management transaction in the exchange network. When a user is to configure a new VLAN for a VTP server, you can allocate VLAN through all switches in the domain, which avoids the same VLAN everywhere. VTP is the Cisco Private Agreement that supports most Cisco Catalyst series products. Through VTP, all switches in its domain know all VLANs, but when VTP can establish excess flow, the case exceptions. At this time, all unknown unicasts and broadcasts are spread throughout the VLAN, allowing all switches in the network to receive all broadcasts, even if the user is not connected in the VLAN, the situation is no exception. The VTP pruning technology is eliminating the extra flow. In the default mode, all Cisco Catalyst switches are configured as a VTP server. This situation is suitable for small networks with small VLAN information and is easy to store on any switch (NVRAM). For large networks, since each switch will perform NVRAM storage operation, this action is redundant for some point, so a "Judgment Call) must be set at these points. Based on this, the VTP server used by the network administrator should adopt a good switch, and other switches are used as clients. It is also necessary to have some of the VTP servers to provide a certain amount of redundancy required to network. So far, VTP has three versions. The VTP V2 is not very different from the VTP V1, mainly different from: VTP V2 supports token ring VLANS, and VTP V1 does not support. VTP V2 is usually only used when using Token Ring VLANS, otherwise VTP V2 is not used. VTPv3 cannot directly handle the VLANS transaction, which is only responsible for the assignment tasks of the opaque database in the Administrative Domain. Compared to the first two editions, VTP V3 has the following improvements:
Supports extended VLANs. Support for the creation and advertisement of dedicated VLANs. Provide server authentication performance. Avoid the "Error" database to enter the VTP domain. Interact with VTP V1 and VTP V2. Support for an ON a per-port basis configuration. Supports propagation VLAN databases and other database types.
Protocol structure
The VTP head structure format can be changed, depending on the type of VTP information. But they all include the following fields:
VTP protocol version: 1, 2 or 3. VTP information type:
Summary Advertisements Subset Advertisement Advertisement Requests VTP Join Messages Administrative Domain Size Dome Data Summary Advertisements When the switch receives a Summary Advertisement packet, it compares the VTP domain name of the packet than its own VTP domain name. If the name is different, the switch ignores the packet. If the name is the same, then compare the configuration revision of both. If the switch has revised the revision of the Summary Advertisement packet above or equal to the sent Summary Advertisement packet, then ignore the packet. Conversely, send an advertising request (ADVERTISEMENT REQUEST). Summary Advert Packet FormatFollowers indicates that the packet follows a Subset Advertisement packet. Updater Identity represents the last IP address of the switch that adds a configuration revision. Update TimeStamp refers to the date and time of the final increment of the revision. Message Digest 5 (MD5), in the case of configuring your password, used to transmit the VTP password; also used to authenticate the validity of the VTP update. Subset Advertisements When you need to add, delete, or change a VLAN in the switch, a changed server switch increases the configuration revision and sends a summary advertisement, followed by one or more subset advertisements. A SubSet Advertisement includes a list of VLAN information. If there are multiple VLANs, you need more Subset Advertisement to adware all VLANs. Summary Advert Packet Format The following table represents the information contained in each different VLAN information (the least first occurred in the ISL VLAN ID value): Different VLAN Information Fields include that most of the data in this packet is easier to understand. This mainly shows the following two points:
This field value in the code - Ubset Advertisement is 0x02. SEQUENCE NUMBER - NE means a data package sequence in the packet stream after Summary Advertisement. The serial number starts from 1. Advertisement Requests In the following cases, the switch requires VTP Advertisement Request:
The switch is resetting; the VTP domain name is changed; the switch receives VTP summary advertisements higher than you configure. Once the Advertisement Request is received, the VTP device sends a summary advertisement, followed by one or more Subset Advertisement. Examples are as follows: Advertisement Requests
The field value in the Code - Advertisement Request is 0x03. START VALUE - Suitable for multiple Subset Advertisement. If the first (n) subset Advertisement has been received, the subsequent (n 1) has not received it yet, Catalyst sends only an Advertisement request from subsection (N 1) Subset Advertisement.
