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Cisco Bug: CSCum91811 - Switching loop occurs when removing DTP from port-channel.

Last Modified

Apr 18, 2019

Products (1)

  • Cisco Catalyst 4000 Series Switches

Known Affected Releases

15.1(2)SG2.80 15.1(2)SG3.0.9

Description (partial)

After disabling DTP on the port-channel BLK port went on FWD state

When you enter the "no switchport nonegotiate" command to disable DTP, port channel members reconfigure the settings and go back UP; the switch on which you apply the nonegotiate command stops receiving BPDUs (the other side still sends and receives BPDUs correctly) and an L2 loop occurs as both switches become the root for STP domain.

Issue seen on below image.
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