Separating the spanning-tree instances - Stacked 3750

[utawakevou]

Got a stacked 3750 with 20 VLAN's. Planning to use it as our core routing but first I need to create 2 spanning tree instance. At the moment its our core switch. Aurguably it is also our SAN as block-level iscsi storage is being carried through them. Got 4 VLAN's for iscsi and want to separate these 4 VLAN's into one instance so that  iscsi vlans should be independent of any fluctuations caused by events on the wider LAN. Am a bit anxious about fluctuations caused by events on the other VLAN's when we convert it as our core router and it might take too long to recover – virtual machines will have packetloss accessing their disks. This Cisco is also the root bridge and we got MSTP running with the default instance.

Want to create another instance and just have VLAN 28, 29,30,31 as the vlans to be included in that instance. Just leave the rest of the VLAn's on the other or current instance. Just need advice and command referencence in how to go about doing this.

Show spanning-tree and spanning-tree mst configuration attach herewith.

Thanks for the help

[andtoth]

Hi,

The Cisco Catalyst Switches are running per-vlan Spanning-Tree. That means each vlan is a separate STP instance. As I understand you refer to MST, which allows several VLANs to be mapped to a reduced number of spanning-tree instances.

For more details and configuration examples, please refer to the following documentations.

Configuring MSTP on Catalyst 3750 Switches

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_55_se/configuration/guide/swmstp.html

Configuration example to migrate Spanning Tree from PVST+ to MST

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml

Understanding Multiple Spanning Tree Protocol (802.1s)

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml

Best regards,

Andras

[utawakevou]

Thanks Andras. Im already running MSTP

[andtoth]

Please review the mentioned documentations in order to achieve your desired configuration with MSTP.

Best regards,

Andras

[Reza Sharifi]

As per attachment you are currently running MST0, which is the default MST.  If you want to move vlan 28-31 to a new instance, then create a new instance and move the vlans to it.  Here is an example of MST1

spanning-tree mst configuration

instance 1 vlan 28-31

C3750-E(config)#do sh spa vlan 28

MST1

  Spanning tree enabled protocol mstp

  Root ID    Priority    32769

             Address     001b.5400.4474

             This bridge is the root

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

             Address     001b.5400.3380

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

C3750-E(config)#

HTH

Reza

[utawakevou]

Thanks Reza for the reply. How about naming and revision when configuring those instance ? Are they optional ? Was going through some examples and notice name and revision 10

[Reza Sharifi]

The default revision number is 0.  You can change it to match the instance.  You can also give a name (optional)

HTH

[Mohamed Sobair]

Hello,

You have bridges connected to your core 3750 running PVST+.

I would recommend migrating all switches To MSTP, if you have to leave it this way, then always make the root the MSTP bridge. Notice , you can't have loadbalancing with this type of setup.

In such scenario, I would always leave your configuration as it's because it made sure the root is the MST bridge inside the region.

On the other hand, instance 0 is the default MST instance the (IST), it's special instance that carries the IEEE BPDU. Hence when it communicates with the PVST+ bridge they should understand each other since the vlan 1 is also sent to the IEEE address for the PVST+.

Before changing to two instances MSTP, please migrate all MSTP or RSTP at least since RSTP is really backward compatible with MSTP.

Regards,

Mohamed

Sent from Cisco Technical Support iPhone App

[utawakevou]

Thanks Mohammed. I got a combination of HP and Cisco in my network environment. HP are aslo running MSTP.

[Mohamed Sobair]

Besides the HP, does all your Cisco bridges run MSTP?

Regards,

Mohamed

Sent from Cisco Technical Support iPhone App

[utawakevou]

Got only one stacked 3750 which is currenly the core switch and we want to move the core routing to it as well which is currently handled by one of the HP switch