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VTP Messages..

Discussion in 'Routing & Switching' started by domdo, Mar 25, 2012.

  1. domdo

    domdo New Member

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    Hi all, just signed up and got my first question for you..!

    Currently studying for CCNP SWITCH. There are three types of VTP message (that you learn about for CCNP anyway): summary advertisements, subset advertisements, and advertisement requests. The way I understand it, is that when a switch receives a summary advertisement with a higher revision number than it's own (assuming the VTP domain also matches), it will send an advertisement request. Then, when other switches receive that advertisement request, they will send a subset advertisement to the device with the lower revision number, which will update it's VLAN configuration based on the information in the subset advertisement. Correct me if I'm wrong already..?

    What I don't fully understand is what the point in the advertisement request is. Cisco say that when you add/delete/change a VLAN on a server, it will send out a summary advertisement followed by a subset advertisement. So if the switch with the lower revision number will be receiving a subset advertisement after the summary advertisement anyway, why does it need to send out the advertisement request (for a subset advertisement which is already being sent anyway)?

    I was thinking it may be because not *all* summary advertisements have a subset advertisement sent after them? I know that VTP servers send a summary advertisement followed by a subset advertisement following a VLAN configuration change. But summary advertisements are also sent every 5 minutes.. Are these periodic subset advertisements maybe not followed by subset advertisements automatically?

    Thanks!
     
    Certifications: CCNA
    WIP: CCNP
  2. cisco lab rat

    cisco lab rat Megabyte Poster

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    Have you tried wiresharking the VTP messages when changes are made to the switches?
     
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  3. domdo

    domdo New Member

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    Hi lab rat, thanks for the reply - I haven't actually got my own lab or equipment, I'm afraid!
     
    Certifications: CCNA
    WIP: CCNP
  4. cisco lab rat

    cisco lab rat Megabyte Poster

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    I would strongly recommend that you invest in some hardware, sell the television plus all your furniture and buy the hardware, for the CCNP ideally you will need at a minimum 2 x 2950's and 2 x 3550 switches. Once you have the kit you will motor through the CCNP SWITCH.

    Do you work with Cisco Devices ?

    Cheers

    Joe
     
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  5. domdo

    domdo New Member

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    Yeah, I do keep meaning to buy some. No idea where I'd put it though! I don't own a TV (better things to do) or any of my own furniture (I rent a flat that's furnished by the owner), so afraid they're not options for me.. ;)

    Yes, I already work in networking for a large organisation who uses mainly Cisco kit. I've had a flick through all the SWITCH material already, didn't see any commands that were completely new to me - nice difference compared to when I did my CCNA (before I had any practical experience)! Not saying I don't need any more practice for the exam, but the job is definitely a big help.

    Any idea about my question? If periodic summary advertisements are followed up by subset advertisements automatically? Cisco don't really seem to tell you anywhere.. The page I've been reading is the first result when you Google "vtp messages", by the way - I can't link to it yet as I'm still a new member?

    Cheers!
     
    Certifications: CCNA
    WIP: CCNP
  6. domdo

    domdo New Member

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    Just in case anyone is wondering the same thing - I started a thread on the Cisco forums, and was told there that subset adverts are *not* sent automatically after the summary advert. They are only sent in response to advertisement requests.
     
    Certifications: CCNA
    WIP: CCNP

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