Spanning Tree Loop :(

[gavin.mckee]

Hi,

I have just added a new stack of 2 3750 Switches to my network. See the attached diagram (SW2) is the new switch stack.

When I had finished adding the configuration to CatOs on the 6509 (Hybrid Mode) I starting getting the following syslog every (approx) 15 mins.

Nov 21 18:59:57 itgedcat1 2006 Nov 21 18:59:56 IST +00:00 %SPANTREE-2-CHNMISCFG: STP loop - channel 3/3,3/17 is disabled in vlan/instance 150 Nov 21 18:59:57 itgedcat1 2006 Nov 21 18:59:56 IST +00:00 %SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-0e-38-a1-68-c2, 00-18-73-6b-e8-18 Nov 21 18:59:57 itgedcat1 2006 Nov 21 18:59:57 IST +00:00 %ETHC-5-PORTFROMSTP:Port 3/3 left bridge port 3/3,3/17

I backed out my changes i.e. those that added SW2 to the 6509 and it still placed the 3/3 and 3/17 ports in an errdisable state.

I can't see why a span loop is happening.

Any help will be rated highly.

Thanks

Gavin

[gavin.mckee]

Thanks Ankur,

I picked up on the restrictions regarding etherchannel modes for cross stack, so thanks for pointing that out anyway.

I'll try the configuration again this evening out side of production time.

Could you give me some CatOs commands that will help debug the errdiable,channel and STP problems if they arise?

Thanks

Gavin

[ankbhasi]

Hi Gavin,

I will really wait to get the status of your network after you put your stacked switch back again? But looking at your config I will recommned you to have desirable between SW1 and Cat6509 also. I see currently it is desirable on 6509 and mode "ON" on SW1.

Also you will not find much debugs on CATOS but certainly you can go through few links for very common error messages and possible workarounds

http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml#Port_or_interface_status_is_errdisable

http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml#PAGP-5-PORTTO__FROMSTP_and

http://www.cisco.com/en/US/customer/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml

Some etherchannel errors

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_7_3/msg_gd/emsg.htm#wp1015352

Some spanning tree messages

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_7_3/msg_gd/emsg.htm#wp1016207

HTH

Ankur

*Pls rate all helpfull post

[glen.grant]

Whereever you can I would set the etherchannel to desirable non-silent on both ends . In a 3750 crossstack etherchannel you can't do this and you have to force it on in which case I would make both ends as on . A little blurb in the 3750 etherchannel guide .Wish they would fix that stipulation.

Caution You should exercise care when setting the mode to on (manual configuration). All ports configured in the on mode are bundled in the same group and are forced to have similar characteristics. If the group is misconfigured, packet loss or spanning-tree loops might occur.

[sundar.palaniappan]

Gavin,

You may want to use the following command in global config mode to detect and put the port(s) in error disabled state if the switch detects any parameter mismatch at both ends of the channel.

spanning-tree etherchannel guard misconfig

This would mitigate the impact of misconfigured etherchannel configuration/parameters and can avoid STP loops as well.

HTH

Sundar