Ravi,
The amber ports are correctly identified in the PT snapshot. Your analysis is incorrect. When Sw2 and Sw3 elect their root port, because of the same distance to the root bridge through both Sw0 and Sw1, the next tiebreaker is the lower Sender Bridge ID. If you watch closely, the Sw1 has a lower BID than Sw0, therefore, switches Sw2 and Sw3 choose their link to Sw1 as their root link because that is the link receiving the best BPDUs.
The remaining port on both Sw2 and Sw3 cannot be a root port, so the only remaining role it can have is designated or non-designated. Here, sent and received BPDU are compared. Because quite obviously, Sw2 and Sw3 are farther from the root bridge than Sw0 and Sw1, the BPDUs sent from Sw0 and Sw1 are better. Hence, Sw0 and Sw1 will have their ports unblocked, and Sw2 and Sw3 will block these ports.
Remember that the order of values compared between BPDUs is:
- Root Bridge ID (= Priority + VLAN + MAC address)
- Total Root Path Cost
- Sending Bridge ID (= Priority + VLAN + MAC address)
- Sending Port ID (= Priority + Port index)
- Receiving Port ID (=Priority + Port index)
The lower value is better.
Best regards,
Peter
