Austin's SWE Notes 😭

    VTP (Vlan Trunking Protocol)

    vtp support central configuration of vlan, so that you don't have to manually manage each vlan.

    vlan names and number can be managed at central switch, configurations will then be distributed to other switches.

    VTP domain: group of connected switches with the same VTP domain configured. These group of switches will share the same VLAN settings.

    [!note]
    Switches with mismatched VTP domains will not negotiate trunk protocols.
    If you wish to negotiate trunk protocol, you need to set the their port mode to trunk (DTP (Dynamic Trunking Protocol))

    [!important]
    Propretiatry protocol from Cisco. Can impact the configuration so best practice to disable it

    Mode

    1. VTP server: any switches can be VTP server.
      • VTP server store the update
      • VTP server can also help to transfer the data to another switch
    2. VTP client: receive the update from VTP server, and configure on itself
      • For switches that are VTP client, VLAN cannot be configured
    3. VTP transparent: don't update the config but transfer it to other swirches.
    4. VTP off: does not participate in the VTP process, will not updating nor forwarding

    Some switches are default to VTP server or VTP transparent.

    Process of VTP

    1. When there are changes for VLAN, VTP servers will send out Initial Summary Advertisement.
      • This initial summary advertisement doesn't contain anything much just the revision number and the domain name
    2. VTP Client receive the summary advertisement. It will check:
      1. Does the domain name matches with what we have?
      2. Does the revision number >= than the current revision number i have?
        If these 2 are true, it will then go ahead and send a advertisement request
    3. The server then respond this advertisement request with another summary advertisement and subset advertisement.
      • These advertisements now contains actual VLAN information for the client to update. (The initial summary advertisement doesn't have this)

    [!important]
    Why are they sending 2 summary advertisement? The second one is a confirmation that the server still have the same information intact (comparing with the initial advertisement)

    So what happen when there are 2 VTP servers update the same configuration differently? Then the one that update first or get acknowledge first will be honored because of the revision number.

    This concept is similar to Optimistic Locking

    Danger of VTP

    Imagine a standalone network switches get connected to a set of stable switches. Since the revision number is different, the stable switches will update its configuration and potentially let to numerious problem in the network.

    As the result, the use of VTP should be executed very carefully.

    Some of the environment which doesn't need constant VLAN changes should not be using VTP at all.

    When updating VTP there should be procedure to follow or install a VTP password.

    ← VSS
    VTP Password →