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Webcast-Catalyst9k
New Member

bpdu's

am I right in saying all switches send bpdu's every 2 seconds? or is it just the root bridge that sends the initial bpdu and then each switch relays this every 2 seconds ?

5 REPLIES

Re: bpdu's

Once a root switch is decided, the configuration bpdu's are sent only form the root bridge and other switches just propogate them as they are received.

Narayan

Re: bpdu's

Just one small addition to Narayan's posting. The other switches propagate the BPDUs, but they do also add their own information each BPDU, such as adding to the path cost.

Kevin Dorrell

Luxembourg

New Member

Re: bpdu's

what happens when a port goes up and down, does the switch send a tcn out to other switches, and do they propagate this to there neighbouring switches also ?

Re: bpdu's

TCNs are directed towards the root switch and hence will be sent out of the root port.

Narayan

Re: bpdu's

Hi,

Normal BPDUs is sent out from the root bridge every 2 sec, BPDU format include lots of fields like Bridge-ID, COST, hellow, forward delay timer , maxage timer, port-id ...

If a designated switch doesnt hear from a root within 20 sec , the root declared dead.

The root-bridge Sends TCA flag to all designated switches on their RPs.

The TCN is sent out RPs from the designated Switch twoard the root-bridge, IF the upstream switch is not the root, it will also mark the TCN and send it out its root port toward the root-bridge.

HTH

Mohamed

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