RAPID-PVST to MSTP migration

Discussion in 'Cisco' started by Armin Kask, Jul 26, 2006.

  1. Armin Kask

    Armin Kask Guest


    In our network there are over 50 switches in a ring. Mostly Cisco Catalyst
    3550 and some 3560.
    Since these platforms do not support more than 128 vlans in RAPID-PVST mode
    we thought we should migrate to MSTP
    Has anybody done this ?
    Any recommendations ?

    Thanks in advance.

    Armin Kask
    Armin Kask, Jul 26, 2006
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  2. Hi Armin,

    Cisco does NOT have any documentation about transitioning from
    Rapid-PVST to MSTP.

    However, you may wish to personally contact Cisco's expert on
    transitioning from Rapid-PVST to MSTP:

    Mr. François Tallet, CCIE No. 3539

    Email: ftallet *at* cisco.com

    François authored Cisco's White Paper:

    Understanding Rapid Spanning Tree Protocol ( 802.1w )


    as well as the Cisco White Paper:

    Understanding Multiple Spanning Tree Protocol ( 802.1s )


    Hope this helps.

    Brad Reese
    BradReese.Com - Cisco Power Supply Headquarters
    1293 Hendersonville Road, Suite 17
    Asheville, North Carolina USA 28803
    USA & Canada: 877-549-2680
    International: 828-277-7272
    Fax: 775-254-3558
    AIM: R2MGrant
    BradReese.Com - Cisco Jobs
    www.BradReese.Com, Jul 26, 2006
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  3. Armin Kask


    Mar 5, 2007
    :hmm2: As an update:
    I contacted François looking for further information on this question, he is a very nice guy. He said that there still nothing available in the way of a migration guide. Though he did offer the following:

    I cannot even pretend that I've spend this time writing a white paper: I still don't know of any. I don't think that it has to be very complex anyway. It all depends on how fast you plan your migration. Generally, we recommend to avoid the interaction between MST and PVST because it is rather complex. If you have to migrate in several steps, I would rather start from the core, because you're less likely to hit some of the complexity introduced by the interaction MST/PVST. While your network is hybrid with a mix of MST and PVST, a reconvergence in the MST part (which should be fast), might isolate the MST region from the PVST regions for about 30 seconds. That's because a network correctly configured for MST is only made of point-to-point connecting to MST bridges or ports configured as edge ports (with portfast enabled). That's something you must be very careful about: if you want the benefit of MST, you need to be able to fulfill those two conditions. This is generally not a big deal in modern networks.​

    :stupido3: My solution may make me sort of a "MOTO", but I thought it worth documenting since there is so little information out there. It may not work for all networks, though a well-designed network should make the basic principals at least feasible. After running simulations in the lab I found that it worked best to simply take whatever steps are necessary (this may be rather involved if you do per-vlan load balancing across redundant links), to shut off all redundant links in the network to remove any hardware loops. Then simply follow the appropriate Cisco/hardware manufacturer online guides for configuring MST on your equipment. (Enabling MST on a device removes any previous PVST configuration.) The configuration is straight forward though do read the whitepapers referenced above if you are unsure about how any part of this works. Start MST on each device then test by re-enabling a single hardware loop during maintenance time. Assuming you have all links set as point-to-point, and your equipment supports it, you will experience the convergence of STP as a complete non-event, (due to RSTP), in all but the most complex networks. Simply repeat this process to restore all redundant links. If you do experience a convergence that lasts a long time (>30 sec) you simply shut off the last link you enabled and check your configuration. Most modern equipment will converge sub-second if everything is configured correctly.
    I must give the standard disclaimer that I make no promises as to what your results might be when trying this, since I am being very general in my explanation, your mileage may vary.
    Aquasapien, Mar 5, 2007
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