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556 Views 6 Replies Latest reply: Feb 9, 2012 4:14 AM by dragan RSS

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pvst

Feb 9, 2012 2:37 AM

Rohan Jadhav 176 posts since
Jul 12, 2011

in pvst, there is seperate spanning tree for each vlan

there 3 switches

sw0 ,  sw1 and sw2

3 vlans

vlan 1, vlan 2 and vlan 3

 

 

sw0 0007.ECBB.A165

 

sw1 0090.21D4.E069

 

sw2 0002.4A6A.2985

 

i have enable pvst for each vlan

for vlan 1 , sw2  is the root  bridge

now for vlan 2 the bid of switches will remain same as it was in vlan 1 or it going to change

because i think in pvst there is seperate spanning tree fro each vlan

so for vlan 2 and vlan 3 how root bridge election will happen

  • Paul Stewart  -  CCIE Security, CCSI 6,989 posts since
    Jul 18, 2008
    Currently Being Moderated
    1. Feb 9, 2012 2:41 AM (in response to Rohan Jadhav)
    Re: pvst

    The bid should be the same. Therefore if you want different root bridges you need to tweak the priority to a lower value on the switch that you want to become the root for a particular VLAN.

  • dragan 80 posts since
    Jan 7, 2010
    Currently Being Moderated
    2. Feb 9, 2012 2:57 AM (in response to Rohan Jadhav)
    Re: pvst

    Is it clear for you after Paul's replay

  • arteq 1,734 posts since
    Sep 11, 2011
    Currently Being Moderated
    3. Feb 9, 2012 3:39 AM (in response to dragan)
    Re: pvst

    the guidance is don't let the root bridge elect itself; you want the root switch to be the hub of the switched network, and on a switch that is optimally placed in the network... likewise, with per vlan, force all vlans on the root switch to be root as well... makes sense to me... keep it simple with spanning tree; it is THE loop free mechanism for layer 2... you are the administrator of your world...

  • Cristian F. Stoica 361 posts since
    Aug 7, 2011
    Currently Being Moderated
    5. Feb 9, 2012 3:45 AM (in response to Rohan Jadhav)
    Re: pvst

    If not specifically configured, the root bridge will always be the one with the lowest MAC address for all VLANs available.

  • dragan 80 posts since
    Jan 7, 2010
    Currently Being Moderated
    6. Feb 9, 2012 4:14 AM (in response to arteq)
    Re: pvst

    Yes you are right arteq unless you use hsrp and load balancing. VLan 1 and 2 on one access switch, second switch -HSRP Avtive (backup for vlan 2) and root bridge for vlan 1( secondary root for vlan 2)and you have third switch HSRP Avtive for vlan 2 ( backup for vlan 1) and root bridge for vlan 2 ( secondary for vlan 1).

     

    But that is different story.

     

    Regards

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