I am wondering why Root Bridge generates Configuration BPDU at every Hello Timer (default 2 seconds)?
Non-Root Bridges relays the Configuration BPDU and keep the lowest BPDU for each port. Why to keep the lowest BPDU for each port? What happens if a port receives a new BPDU with higher Sender Bridge ID or Root Path Cost?
Good explanation. I would like to provide summarization.
Configuration BPDUs are generated every Hello time (2 seconds) from Root Bridge. A bridge can detect indirect link failure when missing Configuration BPDUs for Max Age time. A bridge can also detect indirect network change like change in any of the 4 important fields in BPDUs: Root BID, Root Path Cost, Sender BID, and Send Port ID.
Each port keeps the lowest Configuration BPDU because a bridge can quickly converge to network change. One example is RP down, the bridge can quickly elect the port with the best Configuration BPDU as new RP. The other example is a port can send superior BPDU of its local copy to suppress the Inferior BPDU received from a neighbor.
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