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What is cisco vtp?

VTP: It is a VLAN trunking protocol, also known as a virtual LAN trunking protocol. It is a Cisco proprietary protocol. The function is that a dozen switches are in the enterprise network. The configuration of VLANs is heavy. You can use VTP protocol to configure one switch as a VTP server, and the other switches are configured as VTP clients, so that they can learn automatically.

VTP use:

Usually, we need to keep the VLAN database synchronized in the entire campus network or in a group of switches in the enterprise network.to ensure that all switches can read the relevant VLAN information from the data frame for correct data forwarding. However, for large networks, there may be hundreds or thousands of switches, and there may be dozens or even hundreds of VLANs on a single switch. If you only manually configure it by network engineers, it is a very large workload, and it is not conducive to future maintenance – every time you add or modify a VLAN, you need to deploy it on all switches. In this case, we introduced VTP (VLAN Trunking Protocol).

To use VTP, you must first establish a VTP management domain. Switches in the same management domain share vlan information, and a switch can only participate in one management domain. Switches in different domains cannot share vlan information.

It is the second layer communication protocol of the OSI reference model. It is mainly used to manage the establishment, deletion and renaming of VLANs in the network domain of the same domain.

When a new VLAN is configured on a VTP server, the configuration information of the VLAN is automatically propagated to all other switches in the local domain. The switch automatically receives the configuration information and keeps the VLAN configuration consistent with the VTP server. This reduces the workload of configuring the same VLAN information on multiple devices and maintains the uniformity of VLAN configuration.

VTP maintains VLAN configuration uniformity through the network (ISL frame or cisco private DTP frame). VTP increases, deletes, and adjusts VLANs at the system level to automatically broadcast information to other switches in the network. In addition, VTP reduces the configuration that can cause security issues. Easy to manage, as long as the vtp server is set accordingly, the vtp client will automatically learn the vlan information on the vtp server.

A VTP domain is also called a VLAN management domain. It consists of one or more switches that share VTP domain names. That is, a VTP domain is a group of switches with the same VTP domain name and connected to each other through a relay link.

The following are the requirements for the VTP domain:

1.Each switch in the domain must use the same domain name, either through configuration or automatically learned by the exchange.

2.The Catalyst switches must be adjacent, that is, adjacent switches need to have the same domain name.

3.Trunk links must be configured between all Catalyst switches.

If any of the above conditions are not met, the VTP domain cannot be connected, and the information cannot be transmitted across the separated parts.

There are 3 types of VTP mode, Server mode , client mode ,transparent mode.

The default configuration of the new switch is pre-configured to VLAN1 and VTP mode is the server. Generally, only one VTP Server is set for the entire network in a VTP domain. The VTP server maintains a list of all VLANs in the VTP domain. The VTP server can create, delete, or modify VLANs, send and forward related advertisement information, and synchronize the vlan configuration. The configuration is saved in NVRAM. Although the VTP client maintains a list of all VLANs, the VLAN configuration information is learned from the VTP server. The VTP client cannot create, delete, or modify VLANs, but can forward advertisements, synchronize vlan configurations, and save configurations to NVRAM.

VTP Transparent is equivalent to an independent switch. It does not participate in VTP work. It does not learn VLAN configuration information from the VTP server, but only has its own VLAN information maintained on the device. VTP Transparent can create, delete, and modify VLAN information on the local machine, and forward the announcement and save the configuration to NVRAM.

VTP message type:

    • Summary Advertisements

By default, the Catalyst switch sends a summary notification message every 5 minutes. The summary notification message informs the current VTP domain name and configuration revision number of the nearby Catalyst switch. When the switch receives the summary notification message packet, the switch compares the VTP domain name in the packet with its own VTP domain name.

If the name is different, the switch will ignore this packet. If the names are the same, the switch compares its configuration revision number with the revision number of the packet. If your own configuration revision number is greater than or equal to the revision number of the packet, the packet will also be ignored. If your configuration revision number is small, the switch will send an announcement request message.

    • Subset Advertisements

When an administrator adds, deletes, or modifies a VLAN on a Catalyst switch, the server switch whose configuration is modified will increase the configuration revision number and send a summary notification message. It then sends one or more subset notification messages. Each subset notification message contains a list of VLAN information. If there are multiple VLANs, the switch will ask the server switch to send multiple subset advertisement messages to advertise all of these VLANs.

    • Request Advertisements

1.Switch restart

2.The VTP domain name is modified.

3.The switch receives a VTP summary notification message, and the configuration revision number of the message is higher than its own revision number.

After receiving the notification request message, the VTP device sends a summary notification message. After that, one or more subset notification messages are sent.

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