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I have three switches I'd like to configure in a loop - a Cisco stack (3750s) and two HP 2900 series. Each is connected to the next with a 10 gig backplane of one form or another.

How do I configure the spanning tree on these systems to make this function correctly? From the documents I've looked at it looks like I need to set both sets of hardware to use MST mode but I'm not sure past that point. The trunking, etc is all set up as needed.

HP Switch 1 A4 connected to Cisco 1/0/1. HP Switch 2 B2 connected to Cisco 2/0/1. HP Switch 1 A2 connected to HP Switch 2 A1.

HP Switch 1

show spanning-tree

Multiple Spanning Tree (MST) Information

  STP Enabled   : Yes
  Force Version : MSTP-operation
  IST Mapped VLANs : 1-4094
  Switch MAC Address : 0021f7-126580
  Switch Priority    : 32768
  Max Age  : 20
  Max Hops : 20
  Forward Delay : 15

  Topology Change Count  : 352,485
  Time Since Last Change : 2 secs

  CST Root MAC Address : 0018ba-c74268
  CST Root Priority    : 1
  CST Root Path Cost   : 200000
  CST Root Port        : 1

  IST Regional Root MAC Address : 0021f7-126580
  IST Regional Root Priority    : 32768
  IST Regional Root Path Cost   : 0
  IST Remaining Hops            : 20

  Root Guard Ports     :
  TCN Guard Ports      :
  BPDU Protected Ports :
  BPDU Filtered Ports  :
  PVST Protected Ports :
  PVST Filtered Ports  :

                  |           Prio            | Designated    Hello
  Port  Type      | Cost      rity State      | Bridge        Time PtP Edge
  ----- --------- + --------- ---- ---------- + ------------- ---- --- ----
  ...
  A1              | Auto      128  Disabled   |
  A2    10GbE-CX4 | 2000      128  Forwarding | 0021f7-126580 2    Yes No
  A3    10GbE-CX4 | Auto      128  Disabled   |
  A4    10GbE-SR  | 2000      128  Forwarding | 0021f7-126580 2    Yes No

HP Switch 2

show spanning-tree

 Multiple Spanning Tree (MST) Information

  STP Enabled   : Yes
  Force Version : MSTP-operation
  IST Mapped VLANs : 1-4094
  Switch MAC Address : 0024a8-cd6000
  Switch Priority    : 32768
  Max Age  : 20
  Max Hops : 20
  Forward Delay : 15

  Topology Change Count  : 19,623
  Time Since Last Change : 32 secs

  CST Root MAC Address : 0018ba-c74268
  CST Root Priority    : 1
  CST Root Path Cost   : 202000
  CST Root Port        : A1

  IST Regional Root MAC Address : 0024a8-cd6000
  IST Regional Root Priority    : 32768
  IST Regional Root Path Cost   : 0
  IST Remaining Hops            : 20

  Root Guard Ports     :
  TCN Guard Ports      :
  BPDU Protected Ports :
  BPDU Filtered Ports  :
  PVST Protected Ports :
  PVST Filtered Ports  :

                  |           Prio            | Designated    Hello
  Port  Type      | Cost      rity State      | Bridge        Time PtP Edge
  ----- --------- + --------- ---- ---------- + ------------- ---- --- ----
  ...
  A1    10GbE-CX4 | 2000      128  Forwarding | 0021f7-126580 2    Yes No
  A2    10GbE-CX4 | Auto      128  Disabled   |
  B1    SFP+SR    | 2000      128  Blocking   | a44c11-a67c80 2    Yes No
  B2              | Auto      128  Disabled   |

Cisco Stack 1

show spanning-tree

...    (additional VLANs)

VLAN0100
  Spanning tree enabled protocol ieee
  Root ID    Priority    1
             Address     0018.bac7.426e
             Cost        2
             Port        107 (TenGigabitEthernet2/1/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32868  (priority 32768 sys-id-ext 100)
             Address     a44c.11a6.7c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te1/1/1             Desg FWD 2         128.53   P2p
Te2/1/1             Root FWD 2         128.107  P2p
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  • Is the Cisco device showing the same thing for the other vlans, and is is set up as MST or PVST? The time since last topology change is concerning (unless that's expected), and might indicate a difference in config between the devices.. but having exactly one port in the topology in blocking state is what we're going for, so that part looks good.
    – Shane Madden
    Dec 5, 2012 at 6:17

2 Answers 2

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The Cisco side isn't configured for MST. Take a look here for specifics, but you need to set the 3750 to use the appropriate mode and assign the various ports in the switch to an instance corresponding to the HP's (likely instance 0, but I don't know their implementation). That should - in broad strokes - get the switches at least speaking the same protocol.

Beyond this, I would highly recommend that you explicitly configure one of the three as the root bridge. This is configured on a per-instance basis - lower switch priority wins. A quick Google search turned up some suggested example configs for interoperability. The document in this link has some appropriate warnings about older IOS revisions, but if you're running something reasonably current it's safe to disregard.

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To Configure the Cisco 3750 to use MST(Multiple Spanning Tree) use the following commands:

spanning-tree mode mst
spanning-tree mst configuration
 name MY_MST
 revision 10
 instance 0 vlan 1-4094
!

On the Procurve side use this configuration:

spanning-tree mode mst
name MY-MST
revision 10
instance 0 vlan 1-4094

That will get them talking the same type of STP. You can use MST to load balance vlans over links by dividing up instances across vlans.

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