STP blocking my CE500

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Aug 14th, 2006
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I've just bought a CE500, and am attempting to link it up to an existing 3560, via the gigabit port on the CE, to a GLC-T gigabit ethernet module on the 3560. When I plug the CE into the 3560, the error indicator comes on, and logging into the CE I find an error message on the gigabit port, This Port blocked by spanning Tree.

The config on the 3560 is:

interface GigabitEthernet0/1

switchport trunk encapsulation dot1q

switchport trunk native vlan 100

switchport mode trunk

The GUI on the CE for the gigabit port is set to Switch, VLAN 100.

Please also find enclosed a diagram of my network, as seen through CNA.

Thanks for any advice that can be offered.


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sundar.palaniappan Mon, 08/14/2006 - 13:20
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Some questions for you.

1. Do you want to trunk between the two switches?

2. If answer to the previous question is yes:

a. are the switchport on both switches configured for the same type of trunking dot1q (or) isl?

b. Have you configured the native vlan to be the same on both ends?

c. Configure the port to trunk and set the encap to dot1q and do not leave the switchport mode to dynamic desirable (default) on either end.

3. If the port is an access port remove the trunk commands and configure it as an access port.

Eg. int g0/1

switchport mode access

switchport access vlan 100

Hope that helps!



malberttoo Wed, 08/16/2006 - 01:57
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Hello Sundar, thanks for your reply.

1. If I understand trunking correctly, then yes I do want to trunk between. I ran out out of room on the 3560, so I purchased the CE500 to add more ports.

a. Port is config dot1q on 3560, not sure about CE as I only have the GUI to tell. Gui is set to "Switch" smartport role, and same VLan as 3560 port.

b. yes

c. The config on the 3560 does not say anything about dynamic desirable; is this implied? Do I need to specifically disable it even if it does not show up in the config?

Thanks for your time,


ananddiwakar Wed, 08/16/2006 - 04:02
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Hi Michael,

CE 500 supports only dot1q so if you are putting the port in "Switch" role. it will enable dot1q trunking.

Can you check on 3560 and check the reason why the port is being blocked.

If you could get the output we will get some idea why if it is being blocked. Also the following link will help you

malberttoo Wed, 08/16/2006 - 08:41
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I'm sorry, I'm pretty much a newb at this, and am not sure what commands I would use to see why that port is being blocked.

I did a 'Show spanning-tree' on the 3560(since the CE complained about the port being blocked by spanning tree). It doesn't tell me anything, but maybe one of you guys?

Thanks again for the time.


ananddiwakar Wed, 08/16/2006 - 23:19
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What is connected to fa 0/5 on 3560. Are there any hubs connected to this switch

malberttoo Thu, 08/17/2006 - 10:15
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If I can refer you to the above .jpg Network diagram, port 5 is how this switch (NorthHangar) is connected to another switch (CommRoom). Beside this, there are no other hubs or switches (other than the CE500 I'm trying to plug in).

Thanks again,


Mohamed Anees M... Thu, 08/17/2006 - 20:34
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what IOS version you are running on the CE 500. is it 12.2.25.FY.?

Is your connectivity working and you are seeing alert led? In this case you can ignore the alert LED or upgrade the IOS to 12.2.25.SEG or later if available.


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