Spanning Tree Channel Loop error

[jmprats]

Hi, I'm trying to configure an LACP channel trunk between a CatOS C6000 and a Dell PowerConnect.

I use mode active in both sides and it works great.

But, when I connect a Catalyst 3750X to the Dell PowerConnect the channel between C6000 and PWC shutdown:

2013 May 16 09:08:20 CEST +02:00 %SPANTREE-2-CHNMISCFG: STP loop - channel 5/19-20 is disabled in vlan/instance 20

2013 May 16 09:08:20 CEST +02:00 %SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-04-6d-43-a4-e2, 70-ca-9b-27-46-99

Any help? What's happening?

How can I avoid that?

Thanks

[Giuseppe Larosa]

Hello Jmprats,

>> Any help? What's happening?

The Dell Powerconnect is propagating Cisco proprietary STP BPDU ( likely PVST or Rapid PVST). These BPDUs are multicast frames from the point of view of the Dell PowerConnect so they are propagated.

When the C6500 receives on the link members the STP BPDUs originated on the C3750X

>> 2013 May 16 09:08:20 CEST +02:00 %SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-04-6d-43-a4-e2, 70-ca-9b-27-46-99

Here are the results of your search through the public section      of the IEEE Standards OUI database report for 00046d:

---

  00-04-6D   (hex)          CISCO SYSTEMS, INC.
  00046D     (base 16)          CISCO SYSTEMS, INC.
                      170 W. TASMAN DRIVE
                    M/S SJA-2
                    SAN JOSE CA 95134-1706
                    UNITED STATES

The best long term solution is to move to MST 802.1s and to run it on all cisco and non cisco devices.

A short term solution may be given by disabling spanning-tree etherchannel misconfig check

spanning-tree etherchannel guard misconfig

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/stp_enha.html#wp1020683

I strongly recommend to go to MST on the long term

Hope to help

Giuseppe

[jmprats]

Thanks

If I disable STP in the C3750 access switch it works.

Maybe can be a solution to disable STP if I mix Dell and Cisco switches and I have a loop free network

Do you agree?

[Giuseppe Larosa]

Hello Jmprats,

>> Maybe can be a solution to disable STP if I mix Dell and Cisco switches and I have a loop free network

>>Do you agree?

I do not agree, STP is needed to prevent the creation of bridging loops, the correct STP mode for a multi vendor environment should be used and that should be MST 802.1s.

Working with STP disabled is not safe.

Hope to help

Giuseppe