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

[mark.edwards]

Hi Gavin,

My guess would be Etherchannel is failing for some reason and causiong a loop.

Can you confirm the ports at each end of the Etherchannel are configured correctly (see below link "EtherChannel Feature Configuration Guidelines and Restrictions")?

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/swcg/channel.htm

Also does the switch indicate why the ports have gone to errordisable (try "show errdisable flap-values").

[gavin.mckee]

Mark,

I think the etherchannel is configured fine. I had SW1 up and running for about 3 months with etherchannel running.

Its when I added this new configuration that problems started with the STP loop.

Do you think I sould clear the config of the 3750 stack and start again? First by adding the two interfaces of the 3750. See if these work then build the port channel?

Thanks

[ankbhasi]

Hi Gavin,

I do not see a port channel config on your cat6509 for your new switch.

I only see a port channel set for 3/3 and 3/17 and not for 3/30 and 3/43 which connets to your stacked switch?

Can you confirm the status please.

Regards,

Ankur

[gavin.mckee]

Ankur,

I did set a port channel on the 6509 for 3/30 and 3/43. However I removed this and disabled the interfaces on the 3750 when the interfaces hept going into errdisable state. I removed the channel-group 1 mode on command on the gi0/1 and gi0/24 interfaces as these were still causing an STP loop. I have only one interface connected from SW1 now. No ports channelling.

[ankbhasi]

Hey Gavin,

So no port channel between 6509 and SW1 right? and in this setup what behavior your see? Is the post going into errdisable state and if yes which port? and also in logs can you see the reason for errdisable state?

Ankur

[gavin.mckee]

Ankur,

If you look at the diagram I had SW1 up and running for about 2 months with the Etherchannel working fine. No STP problems at all. When I added the SW2 yesterday STP loops started to happen. I don't have great experince with CatOS so I may be doing something wrong. Is there a problem using channel-group 1 mode on (in SW1) and channel-group 1 mode on on SW2.

Also as the 3750 is in a stack I am using cross stack etherchannel.

Why when I have removed SW2 from the configuration would SW1 contine to have its ports placed in a errdisable state?

Thanks

Gavin

[mark.edwards]

The channel-group number is locally significant so no issue with using the same number on SW1 aqnd SW2. If you have missconfigured the Etherchannel anywhere normal behavior would be for the channel not to work and STP (assuming this is configured correctly) would block one of the 2 links.

I think to get to the bottom of this you need to see why ports are going to error disable. Is there any reason in the log for this?

When a port goes errordisable it may or maynot stay that way depending on how the errordiable recovery is configured. You can configure ports to go errordisable for a number or reasons (the below are defauls for 3550). Under this I list the default recovery reasons for 3550. As you can see the automatic recovery by default are not enabled so a manual recovery is necessary.

switch2#show errdisable detect

ErrDisable Reason Detection status

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

udld Enabled

bpduguard Enabled

security-violatio Enabled

channel-misconfig Enabled

psecure-violation Enabled

vmps Enabled

loopback Enabled

unicast-flood Enabled

pagp-flap Enabled

dtp-flap Enabled

link-flap Enabled

l2ptguard Enabled

gbic-invalid Enabled

dhcp-rate-limit Enabled

unicast-flood Enabled

storm-control Enabled

ilpower Enabled

arp-inspection Enabled

switch2#show errdisable recovery

ErrDisable Reason Timer Status

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

udld Disabled

bpduguard Disabled

security-violatio Disabled

channel-misconfig Disabled

vmps Disabled

pagp-flap Disabled

dtp-flap Disabled

link-flap Disabled

l2ptguard Disabled

psecure-violation Disabled

gbic-invalid Disabled

dhcp-rate-limit Disabled

unicast-flood Disabled

storm-control Disabled

arp-inspection Disabled

loopback Disabled

Timer interval: 300 seconds

Interfaces that will be enabled at the next timeout:

[sourabhagarwal]

Hi Gavin,

i guess you are trying to create layer 3 etherchannel between SW1 and 6509, SW2 and 6509.

if it is correct you need to assign IP to portchannel interface and you don't need to make interface on SW1 and SW2 member of VLAN 150 or you can make port channel member of VLAN 150.

I guess what is happening is there are 2 redundant connections between 6509 and SW1, SW2 as interfaces on SW1, SW2 are not logically binded to single interface , thats why loop is occuring and ports are going to err disable state.

see below URL to configure layer 2 layer 3 etherchannels.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a008007e6d3.html#wp1033712

rate if it help or let me know if you have any questions.

[gavin.mckee]

I don't think its a layer 3 channel i need here, as I need to extend VLANS from the 6509 down into SW2 and SW1. SW1 has machines in VLANS 150 and 151 and they are working fine.

If you had a blank slate here how would you configure this?

Thanks

Gavin

[mark.edwards]

Hi Gavin,

the error message related to missconfigured ehterchannel. Please see this link.

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

[ankbhasi]

Hi Gavin,

Can you please attach the complete config of your 3750 stacked switches as I have a doubt with that only and also paste the relevant config from your CAT6509 related to stack switches.

There should not be any problem when using the same port channel number on 2 different switches as port channel numbers are locally signifcant. Also cross stacked etherchannel should be ok.

Let us review the complete confgi from 3750 stacked switch. Also if your SW1 is in errdisable state shut and then no shut the errdisable port and it should come up.

Regards,

Ankur

[gavin.mckee]

Ok,

I have blew away the configuration on the 3750 switches, so I can't post that. I have a blank canvass here.

As I said above if anyone wanted to configure the topology in my drawing what would your configuration look like?

Thanks

Gavin

[rgodden]

i would try mode desirable instead of on (both ends), had a similar problem to this and that solved it.

[ankbhasi]

Hi Gavin,

You cannot have desirable mode set when the etherchannel is on different switches in a stack.

"Desirable" keyword is not supported when EtherChannel members are from different switches in the switch stack.

I will recommend you to have "ON" on both the sides and I believe it shuould resolve your issue.

Also on your existing etherchannel between SW1 and cat6509 either make it "ON" both the sides or make it "DESIRABLE" on both the sides.

HTH

Ankur