Preventing VTP Database Corruption via Revision Numbers

200-301 By islever Editorial Last updated

Configure and verify VLANs (normal range) spanning multiple switches

Short answer

A Add the switch in the VTP domain with a lower revision number to ensure it syncs from the existing network rather than overwriting the VLAN database.

Question

An engineer needs to add an old switch back into a network. To prevent the switch from corrupting the VLAN database, with action must be taken?
  1. Add the switch in the VTP domain with a lower revision number. Correct Answer
  2. Add the switch in the VTP domain with a higher revision number.
  3. Add the switch with DTP set to dynamic desirable.
  4. Add the switch with DTP set to desirable.

Key Takeaways

VTP uses the highest revision number to determine the authoritative VLAN database; a switch with a higher number can overwrite all others, so a new switch must start with a lower number.

Learn how to safely reintegrate an old switch into a VTP domain by ensuring its configuration revision number is lower than the active network to prevent VLAN database corruption.

Common mistake: Choosing B (higher revision number) because one mistakenly believes a 'higher' number implies authority or freshness, ignoring that VTP propagates the highest number regardless of whether it contains correct or obsolete data.

Expert Analysis

The core issue involves VTP (VLAN Trunking Protocol) behavior regarding configuration revision numbers. In a VTP domain, switches synchronize their VLAN databases based on the highest configuration revision number received. If an old switch with a stale but higher revision number is connected, it will propagate its outdated VLAN information to the entire domain, potentially overwriting the current, correct VLAN database—a catastrophic event known as a 'VTP wipeout.'

To prevent this corruption, the engineer must ensure the new/old switch does not possess a higher revision number than the existing active switches in the domain. Therefore, the switch must be added with a lower revision number. This ensures that when it joins the domain, it receives the authoritative VLAN database from the other switches rather than forcing its own data onto them.

Comments highlight confusion between the direction of the revision number change. Some argue for 'higher' thinking it means 'more powerful,' but technically, a higher number signifies newer/more recent changes. Since we want the existing network's data to prevail, the incoming switch must have a lower number so it accepts updates. Option A correctly states adding the switch with a lower revision number.

Official Reference

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_40_se/configuration/guide/scg1/swvtp.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When dealing with VTP questions, always identify which switch has the highest revision number. Remember that VTP is aggressive: it trusts the highest number blindly. To protect the network, any new device must be initialized with a lower revision number (often by changing the domain name temporarily to reset it to 0) before joining the production domain.

Frequently Asked Questions

What happens if I connect a switch with a higher VTP revision number?

It will propagate its VLAN database to all other switches in the domain, potentially overwriting the correct configuration and causing network outages.

How do I reset a VTP revision number to zero?

You can change the VTP domain name to a temporary unused name and then back to the original, or switch the mode to Transparent and back to Server/Client.

More 200-301 FAQ →

Community Votes

A
67%
B
33%

67% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 17 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 17

  1. Customexit 👍 14 Answered A
    One danger of VTP: If you connect an old switch with a higher revision number to your network (and the VTP domain name matches), all switches in the domain will sync their VLAN database to that switch.
  2. UmbertoReed 👍 9
    This source verifies that the correct answer is "A". Did you type wrong or did you misunderstand the source?
  3. laurvy36 👍 8
    if you put a switch with higher revision number will f...k up the database of the other switches, if you put a switch with lower revison number, it will update the database according with the other swithces
  4. schleef 👍 5
    In real life you would just put a switch in transparent mode...
  5. samuraipizza26 👍 5
    Wording error on my part. A is correct. Thanks
Show 12 more comments
  1. bitree 👍 3
    whether A or B, The switch has to have the lower revision number, not the VTP domain. They should have used more words to make that clear. Likely the answer is A because if you're putting in a switch, you're going to do it regardless of what the VTP domain is currently set up as. and so, the "with a lower revision number" likely refers to the switch.
  2. LOST40 👍 3
    Absolutely not! You're on drugs. Two ways to prevent network breakdown: a). change VTP domain to an unused domain, will reset the REVISION number to ZERO. b). Change the VTP mode to transparent in order to reset the REVISION number to ZERO.
  3. CRP098274 👍 3
    Answer is B Please read the question carefully. The question is pertaining to the old switch from corrupting the VLAN database. It needs the highest revision number in order to prevent from corrupting the VLAN database.
  4. xSora 👍 3
    Why are people answering B? Answer is A.
  5. JulesAZ 👍 2 Answered B
    Just so hard to even understand the question, even before you get into the curriculum! You can read the question 2 ways. But the key for me is that you DONT add an old switch into the network/ domain with a higher revision number than the 'VTP server' So if you read the Question as, 'Add the switch with a lower revision number into the VTP domain', then its A If you read, 'lets make sure we add the switch with rev no (x) to the domain with the highest VTP revision (y) and hope (y) is higher than (x)!!', then its B Id be going B in the exam....
  6. mohdalijmc 👍 2
    ANSWER B I highly suggest you implement some kind of vtp configuration to prevent this in the future. Adding a switch with a higher revision can easily wipe out the vlan configuration on the remaining switches and perhaps that's exactly what happened https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_40_se/configuration/guide/scg1/swvtp.html
  7. dipanjana1990 👍 2
    exactly, that's why i got confused between "A" and "B" because of the selection of the words.
  8. ScorpionNet 👍 2
    A is right because you don't want to mess the database up
  9. ZUMY 👍 2
    A is correct
  10. Babaoa 👍 1 Answered A
    Why Revision Numbers Matter • Higher Revision Overwrites: Switches in VTP Server or Client mode automatically accept and sync VLAN data from any peer that advertises a higher configuration revision number. • The "Wipeout" Risk: If you plug in a used switch that has an older or mismatched set of VLANs but a higher revision number (for example, revision 50 when your live network is at revision 12), the new switch will force its VLAN database onto every server and client in the domain, deleting your active VLANs
  11. samuraipizza26 👍 1
    B Caution Before adding a VTP client switch to a VTP domain, always verify that its VTP configuration revision number is lower than the configuration revision number of the other switches in the VTP domain. Switches in a VTP domain always use the VLAN configuration of the switch with the highest VTP configuration revision number. http://www.securecisco.com/TMCCcisco1234F12/StudyGuide/ccna3/Info/revision.number.htm
  12. xtraMiles 👍 1
    underrated comment

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