%SPANTREE-2-CHNMISCFG: STP loop

[limtohsoon]

Hi Sir,

My network currently has two distribution switches (Catalyst 6513). Please refer to attached diagram for further details.

Yes, it looks weird but I'm actually required to loop two cables from Core2 back to itself. I need to configure both ends in their own etherchannel and different VLANs (359 & 360). The laptops are expected to be able to ping to each other.

After shutting ports 12/6-9 and then configured the necessary, I enabled ports 12/6 and 12/8 just to do a simple test. However, I received the following error messages:

%SPANTREE-2-CHNMISCFG: STP loop - channel 12/8-9 is disabled in vlan/instance 360

%SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-12-7f-27-1a-75, 00-12-7f-27-1a-77

%SPANTREE-2-CHNMISCFG: STP loop - channel 12/6-7 is disabled in vlan/instance 359

%SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-12-7f-27-1a-77, 00-12-7f-27-1a-75

%ETHC-5-PORTFROMSTP:Port 12/8 left bridge port 12/8-9

%ETHC-5-PORTFROMSTP:Port 12/6 left bridge port 12/6-7

I also captured detailed logs on Core2 in the attached file.

Referring to the following technote to troubleshoot, I can't find any reason why this happened. I was only enabling a pair of the links.

Understanding EtherChannel Inconsistency Detection:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a008009448d.shtml

Can someone kindly shed some light on this issue? Secondly, is it a good practice to loop cables to "bridge" two VLANs in typical switching environment? Based on my experience, STP sometimes may converge unpredictably in some switches.

Thank you.

B.Rgds,

Lim TS

[purohit_810]

You can't do intervlan routing between 359 and 360 Vlan.

Why there is specific ewuirement to put two cables between VLAN? Hence it supports intervlan routing on same Box.

It is looping at Layer-2.

Regards,

Dharmesh Purohit

[limtohsoon]

Hi Dharmesh,

This is actually a design proposed by an IPS vendor. They want to deploy the IPS inline to an existing fiber-based GigE WAN link. The IPS, having only RJ-45 ports, has to be deployed in such a way to "bridge" VLANs 359 (to the MSFC) and VLAN 360 (to the WAN link). Please see attached latest diagram.

We actually simulated this setup on another standalone test Cat6513. It works, i.e. a laptop connected to VLAN360 (simulating the remote WAN router) able to ping to the Cat6513's interface Vlan359 IP address, on the same subnet, across the IPS.

However when deployed to production network (as per my diagram), I received the "%SPANTREE-2-CHNMISCFG: STP loop" messages. The test box has the same CatOS version, 10/100/1000Base module, and sup engine as the production box.

Please advise.

Thank you.

B.Rgds,

Lim TS