Issues with RSTP and Rapid PVST (CISCO and DELL hardware)

Zeeshan Siddiqui · ‎12-06-2011

Can you please help with the following

we are adding few Powerconnect 8024F Dell switch on our Network.

The problem we have is we are running RSTP on Dell switches and are using RSTP PVST on cisco 3750 stacks that directly connects to the del switches when we connect the two using trunk ports ideally it should recognise the cisco switch as the root as it has lower spanning tree priority.

What we see on the DEL switch is

Regional Root Path Cost: 0

ROOT ID

Priority 32768

Address 5C26.0AD3.8D06

This Switch is the Root.

Hello Time 2 Sec Max Age 20 sec Forward Delay 15 sec TxHoldCount 6

What we see on the cisco switch is

KB-SR1-6509-1#sh spanning-tree vlan 185

VLAN0185

Spanning tree enabled protocol rstp

Root ID Priority 8192

Address 0011.bc7c.08b9

Cost 3

Port 1669 (Port-channel10)

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

Bridge ID Priority 16384

Address 0011.bc6b.d0b9

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

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

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

Po8 Desg FWD 3 128.1667 P2p

Po10 Root FWD 3 128.1669 P2p

Po12 Desg FWD 3 128.1671 P2p

Vlan 185 exist both on the Del switch and cisco switch and is allowed over the trunk ports adn as you can see we have two Root bridge switches fro the same vlan (we only have a single link connected to the DELL switch)

Is there a risk with the above setup

Kind Regards,

Zeeshan Siddiqui

rais · ‎12-06-2011

Is

Address 0011.bc7c.08b9

the MAC of the DELL switch?

Rais.

Zeeshan Siddiqui · ‎12-06-2011

It is the mac address of the cisco switch (6509 HSRP pair)

A diagram would be

6509-1 ----------HSRP---------- 6509-2 (6509-1 has uplinks to 3750 stack 1 and uplinks to 3750 Stack2)

+ > < + (6509-2has uplinks to 3750 stack 1 and uplinks to 3750 Stack2)

+ > +

+ < > +

3750 stack 1 3750 Stack 2

+

DEL switch (connect to 3750 by a trunk port) vlan allowed on trunk is 185 ) .

Below is output for Sh spanning tree on DEL switch (does not support RAPID PVST)

Regional Root Path Cost: 0

ROOT ID

Priority 32768

Address 5C26.0AD3.8D06

This Switch is the Root.

Hello Time 2 Sec Max Age 20 sec Forward Delay 15 sec TxHoldCount 6

Below is out put on 6509 (avtive member for 6509 HSRP pair on vlan 185) running rapid PVST

Please see output below

VLAN0185

Spanning tree enabled protocol rstp

Root ID Priority 8192

Address 0011.bc7c.08b9

This bridge is the root

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

Bridge ID Priority 8192

Address 0011.bc7c.08b9

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

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

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

Po10 Desg FWD 3 128.1665 P2p

Po12 Desg FWD 3 128.1667 P2p

Po8 Desg FWD 3 128.1672 P2p

Both switches can see each other over the trunks

rais · ‎12-06-2011

Is it correct that VLAN 185 is defined on 3750 stack 1 in VLAN database?

Thanks.

Zeeshan Siddiqui · ‎12-07-2011

Hi rais,

Thanks for your reply

Vlan does exist on the VLAN database. (the 3750 is acting as a layer two switch) in one VTP domain as a VTP client.

The DEL switch is not part of the VTP domain stand alone switch.

Kind Regards,

Zee

JohnTylerPearce · ‎12-07-2011

Well, bpdu's are basically the heart of spanning tree, so maybe they're having issues reading each other bpdus?

What do the port states look like on the trunk connecting the Dell Switch to the 3750.

Zeeshan Siddiqui · ‎12-07-2011

We have allowed another vlan over the trunk ports for testing which is 184

KB-SR3-3750-2#sh spanning-tree int Gi2/0/8

Vlan Role Sts Cost Prio.Nbr Type

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

VLAN0184 Desg FWD 4 128.60 P2p

VLAN0185 Desg FWD 4 128.60 P2p

KB-SR3-3750-2#

There is only one link to the DEL switch

rsimoni · ‎12-07-2011

According to the outputs you attached the Dell switch is running MSTP and not RSTP.

Regional Root Path Cost: 0 <<<

Regions are paramters used in MSTP.

According to Dell datasheets this powerconnect supports 3 flavors of STP.

IEEE 802.1D – Spanning Tree1

IEEE 802.1S – Multiple Spanning Tree

IEEE 802.1W – Rapid Spanning Tree1

http://www.dell.com/us/enterprise/p/powerconnect-8024f/pd

You should check one of the Dell/Cisco STP interoperation guide available on the Internet to get an idea of what to do.

If your 3750 is running RSTP but does not have vlan 185 it is expected that you have more than one root bridge.

I suggest you to change the STP flavor on your Dell box first since apparently you have the option to do that.

Riccardo

Zeeshan Siddiqui · ‎12-07-2011

DELL switch below

console#show spanning-tree summary

Spanning Tree Adminmode........... Enabled

Spanning Tree Version............. IEEE 802.1w

BPDU Guard Mode................... Disabled

BPDU Flood Mode................... Disabled

BPDU Filter Mode.................. Disabled

Configuration Name................ 5C-26-0A-D3-8D-06

Configuration Revision Level...... 0

Configuration Digest Key.......... 0xac36177f50283cd4b83821d8ab26de62

Configuration Format Selector.....

For 3750 below

spanning-tree mode rapid-pvst

spanning-tree loopguard default

no spanning-tree optimize bpdu transmission

spanning-tree extend system-id

VLAN0185

Spanning tree enabled protocol rstp

Root ID Priority 8192

Address 0011.bc7c.08b9 (MAC for 6509)

Cost 3

Port 704 (Port-channel12)

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

Bridge ID Priority 32953 (priority 32768 sys-id-ext 185)

Address 0012.43ba.9680

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

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

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

Po11 Altn BLK 3 128.696 P2p

Po12 Root FWD 3 128.704 P2p (port-channel that connects to 6509)

Gi2/0/8 Desg FWD 4 128.60 P2p

Dell are investigating the problem at there end and plan to migrate the DEL switches from RSTP to MST.

Any know problems when we use Rapid PVST and MST ?

JohnTylerPearce · ‎12-07-2011

Well, if you do that you are going to have separate spanning-tree domains so to speak. You could end up having two root switches for the same vlan. The RPVST will have one and the MST will.

Zeeshan Siddiqui · ‎12-07-2011

Some thing I dont undertsand

When I change the port from trunk to access on both switches (Cisco + DELL) it can see our switch as the root bridge when we change to trunk at both ends you have two root Switches?

.

JohnTylerPearce · ‎12-07-2011

This may sound like a stupid question, but when you set it to trunk, what vlans are allowed across the trunk?

Zeeshan Siddiqui · ‎12-07-2011

They are allowed on the trunk port.

I can connect to the DEL switches over the trunk ports.

JohnTylerPearce · ‎12-08-2011

It almost sounds like when you change the port to access, both switches exchange bpdus, and are able to decide that the cisco switch is the root switch. But if you change it to trunk, bpdus are not exchanged and therefore you end up with separate root switches. Bug maybe, or they may not corporate with that cisco switch ???

Zeeshan Siddiqui · ‎12-08-2011

Hi John

I complelety agree

the next step is we are goign to move the Dell switches to use MST as the DEll switch support MST (have done some testing using cisco switches one of them running rapid PVST and the other MST) we only had one root bridge and when we connected the second link it went to blocking.

The test I did was between cisco switch VS Cisco switch and not DEll vs Cisco (In theory the protocal should work the same)