VTP

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

VTP synchronization is the process by which switches update their VLAN databases to match the latest database version advertised by another switch.

VLAN Trunking Protocol (VTP) is a Cisco-proprietary protocol that synchronizes VLAN databases across switches. The database is stored in vlan.dat, and synchronization can reduce repetitive configuration and human error in large LANs. VTP messages travel only through trunk ports and only between switches in the same VTP domain. section 13.2 section 13.2.1

VTP synchronization follows the database revision number:

• Creating, deleting, or renaming a VLAN increments the revision number. section 13.2.1
• A switch advertises database changes through VTP messages, and another switch synchronizes when the advertised revision is higher. section 13.2.1 section 13.3
• A switch without a configured domain is in domain NULL; it can change VLANs but does not send VTP messages. section 13.2.1
• Use vtp domain domain-name to join a domain and show vtp status to inspect the domain, mode, version, and revision. section 13.2.1 section 13.3

Propagating VLANs

After SW1 joins the Manning domain, creating VLANs 2, 3, and 4 raises its revision to 3. SW2 and SW3 receive the advertisements and update their databases to revision 3, allowing the VLANs to exist across the LAN. section 13.2.1

Figure 13.7 SW4 is connected to the network and overwrites the VLAN databases of SW1, SW2, and SW3. (1) SW4 is connected to the LAN. (2) SW4 sends VTP messages to the other switches. (3) Because SW4 has a higher revision number (50 vs. 5), SW1, SW2, and SW3 synchronize their VLAN databases to match SW4. Hosts in VLANs 10, 20, and 30 will be unable to communicate over the network because their VLANs no longer exist.

Visualize the major VTP failure mode: a newly connected switch with a higher revision can overwrite the VLAN databases of the existing domain. section 13.2.4

VTP can cause outages when a newly connected switch has a higher revision number and the same domain. Reset the revision to 0 before connection by changing the domain away and back; versions 1 and 2 also support temporary transparent or off modes. Version 3 adds off mode, extended-range VLAN support, and a primary server that alone can modify the VLAN database. section 13.2.4 section 13.2.3

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains domains, trunk propagation, revision selection, modes, versions, commands, and outage prevention through worked switch scenarios.

Examples

Uses SW1, SW2, and SW3 propagation, show vtp status output, and a high-revision SW4 outage scenario.

What it assumes

Assumes VLAN databases and trunk ports, while defining VTP domains, revisions, modes, and synchronization behavior.

What you can do after

Operate/configure VTP with vtp domain, vtp version, and show vtp status while preventing revision-number outages.

How it connects

Connects VLANs, VLAN databases, trunk ports, VTP domains, revision numbers, VTP modes, and VTP version 3.

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Related concepts

• extended-range vlanuses · An extended-range VLAN is a VLAN numbered from 1006 through 4094 in Cisco switch VLAN classification.
• VTP revision numberuses · A VTP revision number is a version counter used to determine which VLAN database information should synchronize within a VTP domain.
• vlan databaseuses · A VLAN database is a switch-maintained record of configured VLANs and the ports assigned to them.
• protocolkind of · A protocol is a defined set of rules and conventions governing communication or interaction among systems, components, or participants.
• VTP off modeimplements · VTP off mode is a VTP operating mode in which a switch does not participate in VTP or forward VTP messages.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.