Spanning-tree setup with incompatible switches
- by wfaulk
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?
