BPDU'S

[carl_townshend]

Hi all, Am I right in saying all switches on a network send bpdu's or does just the root send them ?

[vijayasankar]

Hi Carl,

When all the switches are initialising/booting up, they all exchange BPDU's. However once a root bridge is elected, only the root bridge will send the BPDU. All other switches in the network will relay this BPDU to their downstream devices.

Exception to this is when a non root switch detects any change in the network, ( link up/ link down etc) it will generate a Topology change notification BPDU.

This is applicable to 802.1d( STP )

In RSTP 802.1w, all the briges(switches) generate the BPDU and they exchange it with their neighbours.

Hope this clarifies your query.

-VJ

[sourabhagarwal]

When the switches in a network are powered up, each functions as the root switch. Each switch sends a configuration BPDU through all of its ports. The BPDUs communicate and compute the spanning-tree topology.

Switches send and receive spanning-tree frames, called bridge protocol data units (BPDUs), at regular intervals. The switches do not forward these frames but use them to construct a loop-free path. BPDUs contain information about the sending switch and its ports, including switch and MAC addresses, switch priority, port priority, and path cost.