Hi Sonam,
The dispute mechanism was a very nice enhancement that was added into spanning-tree. I'll try to provide some information on it and then we'll move on to how we can find out what's wrong and fix it.
Every segment, as you are probably aware, should have only one designated port. This port (and bridge) is responsible for generating BPDUs for the segment. Now, RSTP onwards, the BPDU format changed a little bit. It now includes the port role as well among other things. The port role is simply the spanning-tree role of the port.
A spanning-tree dispute happens when a designated port receives a BPDU in which the port role is also designated. The bridge that receives and detects this moves it's port to a discarding state - note that the port role still remains designated. The BPDU being received should also have the learning bit set for the dispute to occur.
This entire mechanism is quite helpful in detecting unidirectional situations which can lead to loops.
Let's come back to your scenario now. Could you post the show spanning-tree vlan please? As you said, this port goes to a Maruta encryptor. I'm not familiar with this device but I am assuming that it does not participate in spanning-tree. Is that correct? Are there any other switches connected to this device?
Regards,
Aninda
