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Bring performance and reliability to your network with the Aruba Core, Aggregation, and Access layer switches. Discuss the latest features and functionality of the ArubaOS-Switch and ArubaOS-CX devices, and find ways to improve security across your network to bring together a mobile first solution.
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Spanning Root Bridge MAC Address

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  • 1.  Spanning Root Bridge MAC Address

    Posted Jul 29, 2021 12:43 PM
    Hi,

    When making a 3810M stack the root bridge what is the MAC address used as each physical switch has its own MAC address?

    Thanks,
    Paul.

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    Paul Slade
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  • 2.  RE: Spanning Root Bridge MAC Address

    Posted Jul 30, 2021 04:44 AM
    Just to add we are replacing the two physical core switches with a 3810M stack. The current MSTP root bridge is Core1 MAC address with Core2 as the failover using STP priorities. The 3810M is obviously a single logical switch with two physical switches connected via the back plane and therefore has two MAC addresses. As it is seen as a single logical switch what the is the MSTP root bridge MAC address going to be if we use the same STP priority configuration?

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    Paul Slade
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  • 3.  RE: Spanning Root Bridge MAC Address

    Posted Jul 30, 2021 08:37 AM
    Once an Aruba 3810M stack is well formed (say you have a Commander and a Standby), the Stack's MAC Address is - if I recall correctly - a value calculated using the Commander's MAC Address as the base and once Spanning Tree is enabled (MSTP should be the default) the MAC Address you're referring to should be the one of the already formed hardware stack if I'm not mistaken (that MAC Address should indeed appear referenced to the "Switch MAC Address" parameter as reported when you execute the show spanning-tree command, the same MAC Address is reported also under the "IST Regional Root MAC Address" parameter)

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    Davide Poletto
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  • 4.  RE: Spanning Root Bridge MAC Address

    Posted Jul 30, 2021 12:27 PM
    If MSTP uses the Commander MAC address as the CST Root MAC Address and IST Regional Root MAC Address what happens when the switch which is the current Commander fails and the current Standby becomes the Commander (this is a two switch stack) which has a different MAC address?
    Does MSTP recognise that the root bridge has changed and reconverges on the new Commander MAC address?

    This works on the current core which uses two physical switches trunked together as priority 0 is the primary core switch and priority 1 is the secondary core switch giving us HA as it also uses VRRP. However the 3810M stack will only have one config and therefore only one priority. See below. 

    Current Core 1
    spanning-tree
    spanning-tree Trk1 priority 4
    spanning-tree config-name "BBR"
    spanning-tree config-revision 2
    spanning-tree instance 1 vlan 1 10 14-20 114
    spanning-tree instance 1 priority 0
    spanning-tree instance 1 Trk1 priority 4
    spanning-tree instance 2 vlan 11
    spanning-tree instance 2 priority 1
    spanning-tree instance 2 Trk1 priority 4
    spanning-tree priority 0

    Current Core 2
    spanning-tree
    spanning-tree Trk1 priority 4
    spanning-tree config-name "BBR"
    spanning-tree config-revision 2
    spanning-tree instance 1 vlan 1 10 14-20 114
    spanning-tree instance 1 priority 1
    spanning-tree instance 1 Trk1 priority 4
    spanning-tree instance 2 vlan 11
    spanning-tree instance 2 priority 0
    spanning-tree instance 2 Trk1 priority 4
    spanning-tree priority 1

    New 3810M Stack Core
    spanning-tree
    spanning-tree config-name "BBR"
    spanning-tree config-revision 2
    spanning-tree instance 1 vlan 1 10 14-20 114
    spanning-tree instance 1 priority 0
    spanning-tree instance 2 vlan 11
    spanning-tree instance 2 priority 0
    spanning-tree priority 0


    ------------------------------
    Paul Slade
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  • 5.  RE: Spanning Root Bridge MAC Address

    Posted Jul 30, 2021 12:49 PM
    Hello Paul, I never wrote the stack will use the MAC Address of the Stack Commander, instead (IMHO) it will use a virtual one (the one it generates using the Commander's MAC Address as base when the Stack forms).

    As example (since I haven't an Aruba 3810M stack I used what is reported here) have a look here:

    HP Stack 3800#: show stacking
     Stack ID         : 00031cc1-de4d48c0
     MAC Address      : 1cc1de-4d48c9
     Stack Topology   : Mesh
     Stack Status     : Active
     Uptime           : 1d 2h 35m
     Software Version : KA.15.05
    
      Mbr
      ID  Mac Address   Model                                  Pri Status
      --- ------------- -------------------------------------- --- ---------------
      1   1cc1de-4d48c0 HP J9574A 3800-48G-PoE+-4SFP+ Switch   250 Commander
      2   1cc1de-4d8680 HP J9573A 3800-24G-PoE+-2SFP+ Switch   230 Standby
      3   1cc1de-4e3180 HP J9574A 3800-48G-PoE+-4SFP+ Switch   128 Member
      4   78acc0-3c2180 HP J9576A 3800-48G-4SFP+ Switch        128 Member


    and note that the "1cc1de-4d48c9" is the (virtual) Stack MAC Address - reported ad the MAC Address - while the "1cc1de-4d48c0" is the (real) Stack Commander MAC Address as reported on the stack member list.



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    Davide Poletto
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  • 6.  RE: Spanning Root Bridge MAC Address

    Posted Jul 30, 2021 01:51 PM

    Hi Davide,

    Perfect, thanks for the explanation.

    Paul.