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Virtual chassis : Master election scenario

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  • 1.  Virtual chassis : Master election scenario

    Posted 12-21-2018 11:10

    Hi everyone,

    I have some questions about the master election in virtual chassis.  

    Please consider following scenarios:

     

    We have three switches SW1,SW2,SW3
    All are using default priority.

    We are using dynamic method to form Virtual chassis


    Case#1
    SW1 is master, Sw2 is back, SW3 is a line card. Virtual chasis is formed and 30 minutes have elapsed
    We introduce SW4 with priority 128 into Virtual chassis.

    As per juniper , following is tie breaker:

    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.

     

    Is it not true to criteria (3) above will be used to break the tie? The reason I said that Virtual chassis never booted, we form the Virtual chassis and never booted the Virtual chassis .


    Case#2

    SW1 is master, Sw2 is back up RE, SW3 is a line card. Virtual chasis is formed.
    We reboot the virtual chassis first time . SW1 came up online first, SW2 2nd, SW3 third, Virtual chassis forms with
    SW1 Master
    SW2 Back up RE
    SW3 Line card.


    After 30 minuutes, we introduce SW4 with priority 128 into virtual chassis .
    Following criteria will be used to break the tie:

    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.


    Which crietria above,  will apply to SW4? is it not (2)?

     

     

     Thanks and have a nice weekend!!

     

     

     



  • 2.  RE: Virtual chassis : Master election scenario
    Best Answer

    Posted 12-21-2018 13:25
    It’s been a while that I messed with default values for Virtual Chassis, I believe it’s <3> in this case.

    I will say however, if this is for a production environment please consider statically assigning roles via serial numbers. I can’t tell you the number of times using non-static virtual chassis configurations has caused more issues then added redundantcy (generally after a power failure).

    https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/virtual-chassis-mx-series-preprovisioned-member-info.html

    (On mobile, please ignore mistakes)