Bridge protocol data unit (BPDU)
BPDU can be called as the language of switch. BPDU’s are sent out all ports every two
seconds, are forwarded to a specific MAC multicast address: 0180.c200.0000.
When a switch is "UP" it starts sending BPDU through every ports.If a BPDU comes back to the switch,switch will know there is a redundant link.In such cases switch will run STP.
There are two types of BPDU
- Configuration BPDU
- TCN BPDU (Topology change notification)
When a root receives the TCN BPDU, it transmits a configuration BPDU message on all the ports with topology change flag set to 1. Switches that receive this BPDU on the root port filter the database and generate their own configuration BPDUs on designated ports. This propagates down the tree to the end of the path.
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