VTP Summary Advertisement--> VTP Domain Mismatch (All helpful posts will be rated)

[Vasconcelos]

So,

Whenever a VTP configured Switch receives a VTP Summary Advertisement, it will check whether the Domain Name matches

If the Domain Name doesn't match, then

    - The VTP Server, Client or Transparent (V1) Switch would ignore the Summary Advertisement

    - The Summary Advertisement wouldn't be flooded through its Trunk Ports

If it's a VTP Version 2 Transparent Switch, though, it would ignore the Summary Advertisement, however, it would flood it through all its Trunk Ports except for the one it received it on.

Can anyone say if what I wrote above is correct?

[Francesco Molino · Accepted solution]

Hi

You're right except for transparent vtp v2. 

If you test it in lab, you'll see that even in transparent mode, there's a domain inspection which means if the domain mismatch then the vtp advertisement is ignored.

[Vasconcelos]

The Cisco Documentation below says that a VTP Version 2 Transparent Switch will forward the VTP Advertisement without inspecting the VTP Version or VTP Domain Name

"Version-Dependent Transparent Mode—In VTP version 1, a VTP transparent switch inspects VTP messages for the domain name and version and forwards a message only if the version and domain name match. Because VTP version 2 supports only one domain, it forwards VTP messages in transparent mode without inspecting the version and domain name."


https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_52_se/configuration/guide/3560scg/swvtp.html

[Francesco Molino · Accepted solution]

Yes the doc says that, but test it like this:
SW1 <--> SW2 <--> SW3
Set SW1 as server with domain test and SW3 with domain test as client. Then configure SW2 as transparent with domain cisco.
You should see that SW3 won't get synced.

I've done a quick lab to show you using same scenario as explained before.

My VTP Server (SW1):

Now SW2 as transparent and SW3 as client (all with same domain)

These outputs show that vtp is working as expected and VTP Transparent is forwarding request to SW3.

Now let's keep SW2 as transparent but with domain CISCO instead of TEST.

SW1SW2SW3

As you can see, SW1 revision and vlan numbers are increasing while SW3 not. This shows that there's a domain inspection and if there's a domain mismatch, vtp packets are not forwarded to next switches.

[Vasconcelos]

Thank you for the Lab. I only have two switches, therefore, I can't lab this specific situation

So, on a Cisco Certification Exam, I'll have to follow the documentation, however, this is not what happens in real life.

[Francesco Molino]

I'm sorry but I'm not gonna answer what to do in exams because this is always done tricky situation. I mean do you need to say what's in the documentation or how it works really? Maybe it would be interesting to see if this has been updated in Cisco press and/or new ios doc version.

[Vasconcelos]

Yeah, I understand. Thanks for the help, friend

[Francesco Molino]

You're welcome