Topology Change

Hi All

the core switch our network keeps on getting topology change notification quite often. This happens every-morning. Our core switch is dlink dgs 3627. Earlier I figured out that the the none trunk ports were participating in spanning tree elections. To avoid this I configured all the non trunk ports as the edge ports.

After doing this I still  keep on getting topology change on the core switch and all the other switches. The spanning tree priority on the core switch is set to 4096.

I am kind of lost in the mist here. Can anyone punch in some ideas to help me troubleshoot the issue.

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Don JohnstonInstructorCommented:
A Topology Change Notification (TCN) BPDU is generated by any switch when a network port changes state.

So, if any ports (that are not defined as edge ports) on any switches see an interface come up, a TCN BPDU will be generated.

The only way to stop this is to configure all ports that are not switch-to-switch links as edge ports.

I figured out that the the none trunk ports were participating in spanning tree elections. To avoid this I configured all the non trunk ports as the edge ports.
There must be a couple of ports that are still configured as network ports.

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virkshivrajAuthor Commented:
The question might be dumb, but could it be possible if I unplug the cable from a port on the core switch that is configured to be an edge port and plug it back in, the switch will notice a topology change
Don JohnstonInstructorCommented:
No. Edge port state changes don't cause TCNs.
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virkshivrajAuthor Commented:
Another silly question Don  .. I noticed that I have a wireless controller on which RSTP is configured and the port to which the controller is connected is not set as edge port ..

Should that port be configured as edge port ?

The link between controller and the switch is a trunk link carrying two VLANs. VLAN 21 for wireless device management (controller & access points) and the other one for SSIDs  
Don JohnstonInstructorCommented:
Trust me... I've heard lots of silly questions and you ain't even come close. :-)

Should that port be configured as edge port ?

No. Edge ports are for connections to devices that are not running STP.

virkshivrajAuthor Commented:
thanks Don .. much appreciated

... but i can have an edge port configured as an trunk port and disable STP on the device that is connected to that specific port ..

for example in my scenario .. I can configure the port on which the controller is connected to the switch as an edge port. My reason for this is that since there is only one link between the controller and the core, and this is the the single point of failure, basically no redundant link is configured therefore no looping between the controller and the switch, I think it is not necessary to configure STP on the controller.

What are your views regarding  ?
Don JohnstonInstructorCommented:
First off, forget about the trunk aspect. Trunk, access, tagged, untagged, STP could care less.

Second, if the device is participating in spanning-tree, then the port going to that device should be a network (non-edge) port.

Third, if there's any chance that the port could in any way end up linking back to the network (connects to a location that you have no control over, an access-point, another switch, etc.), do not make the port an edge port.
virkshivrajAuthor Commented:
thanks Don .. that clarifies a lot

I'll consider those recommendations ....

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Networking Protocols

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