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wfaulk
Asked: 2013-06-28 16:09:10 +0800 CST

Spanning-tree setup with incompatible switches

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I have a set of eight HP ProCurve 2910al-48G Ethernet switches at my datacenter that are set up in a star topology with no physical loops. I want to partially mesh the switches for redundancy and manage the loops with a spanning-tree protocol.

However, our connection to the datacenter is provided by two uplinks, each to a Cisco 3750. The datacenter's switches are handling the redundant connection using PVST spanning-tree, which is a Cisco-proprietary spanning-tree implementation that my HP switches do not support.

It appears that my switches are not participating in the datacenter's spanning-tree domain, but are blindly passing the BPDUs between the two switchports on my side, which enables the datacenter's switches to recognize the loop and put one of the uplinks into the Blocking state. This is somewhat supposition, but I can confirm that, while my switches say that both of the uplink ports are forwarding, only one is passing any real quantity of data. (I am assuming that I cannot get the datacenter to move away from PVST. I don't know that I'd want them to make that significant of a change anyway.)

The datacenter has also sent me this output from their switches (which I have expurgated of any identifiable info):

3750G-1#sh spanning-tree vlan nnn

VLAN0nnn
  Spanning tree enabled protocol ieee
  Root ID    Priority    10
             Address     00d0.0114.xxxx
             Cost        4
             Port        5 (GigabitEthernet1/0/5)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32mmm  (priority 32768 sys-id-ext nnn)
             Address     0018.73d3.yyyy
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/5             Root FWD 4         128.5    P2p
Gi1/0/6             Altn BLK 4         128.6    P2p
Gi1/0/8             Altn BLK 4         128.8    P2p

and:

3750G-2#sh spanning-tree vlan nnn

VLAN0nnn
  Spanning tree enabled protocol ieee
  Root ID    Priority    10
             Address     00d0.0114.xxxx
             Cost        4
             Port        6 (GigabitEthernet1/0/6)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32mmm  (priority 32768 sys-id-ext nnn)
             Address     000f.f71e.zzzz
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/1             Desg FWD 4         128.1    P2p
Gi1/0/5             Altn BLK 4         128.5    P2p
Gi1/0/6             Root FWD 4         128.6    P2p
Gi1/0/8             Desg FWD 4         128.8    P2p

The uplinks to my switches are on Gi1/0/8 on both of their switches. The uplink ports are configured with a single tagged VLAN. I am also using a number of other tagged VLANs in my switch infrastructure. And, to be clear, I am passing the tagged VLAN I'm receiving from the datacenter to other ports on other switches in my infrastructure.

My question is: how do I configure my switches so that I can use a spanning tree protocol inside my switch infrastructure without breaking the datacenter's spanning tree that I cannot participate in?

networking

1 Answers

  1. Best Answer

    To interoperate with the Cisco PVST+, you'll want to use MST on your Procurve switches.

    What it sounds like is that you have two different topologies that you'll want to account for:

    • The effective physical topology of the vlan that you share with the provider, and
    • The topology of the rest of your vlans, which don't involve the Cisco switches at all

    For this, what you'll want is two instances of MST:

    • One for just the vlan that touches the Cisco switches, configured on all of the switches that it touches, and
    • One for all other vlans in your environment

    I'm not sure exactly what this configuration will need to look like on the HP switches, but it should essentially be two MST instances on each switch carrying the vlan that touches the Ciscos: one instances with just that vlan configured, and a second instance with all the other vlans configured.

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