Expand all | Collapse all

Dynamic installation Scenario for Virtual chasis mode

Jump to Best Answer
  • 1.  Dynamic installation Scenario for Virtual chasis mode

    Posted 07-15-2017 16:10

    Hi everybody


    Let say we have three EX 4200 switches: SW1, SW2,SW3,  we want to use " Dynamic Installation method" to configure them in a chasis mode.

    We cable VCP ports in daaisy chained ring toplogy. We set up SW1 and SW2 priority as 255, while SW3 has a default priority of 128.

    We power SW1 first then SW2 and finally SW3. They assume following roles:

    SW1--Elected master

    SW2--Back up RE

    SW3--Line card


    Let say we power down SW1, Sw2 assume  master and SW3 BACK UP RE role  now, next we power on SW1. What role SW1 ,SW2 and SW3 assume ?



    The algorithm proceeds from the top condition downward until the stated condition is satisfied:

    1. Choose the member with the highest user-configured mastership priority (255 is the highest possible value). A switch with a mastership priority of 0 will always stay in the linecard role.
    2. Choose the member that was master the last time the Virtual Chassis configuration booted.
    3. Choose the member that has been included in the Virtual Chassis configuration for the longest period of time. (For this to be a deciding factor, there has to be a minimum time lapse of 1 minute between the power-ons of the individual interconnected member switches.)
    4. Choose the member with the lowest MAC address.


     This is my hunch based on the above:


     When SW1 powers up and join the Chasis, SW3 will assume LINE CARD ROLE because it has the lowest priority of 128.

    SW1 and SW2 have the same priority of 255 so 2nd criteria is used i.e who has the more time in the chasis, since SW1 just joins Chasis therefore SW2 remains Master and SW1 assumes BACK UP RE role.


    Am I correct?


    Thanks and have a nice weekend!!




  • 2.  RE: Dynamic installation Scenario for Virtual chasis mode
    Best Answer

    Posted 07-15-2017 17:11

    Yes, but as I stated previously a small amount of one-time config work to pre-provision the VC, will save you from guessing.  Turning on GRES, NSB, NSR who cares is some SW preempts to re-takeover Master, network will run as if nothing changed.  With pre-provision (again I think best practice recommendation) you'll always know which SW are RE's and which are line cards.


    Dynamic protects better against double-fault of both RE SW's, but likelihood of this happen is VERY remote.