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JaySu
Beginner

Switch still send BPDU in whole listening state?

Hello experts,

 

I just finished my CCNA course and try to dig more about STP. I have some questions may need your help. Thanks.

 

1.) Does a switch keep sending BPDU(7 times because send Hello every 2 seconds and listening state remains for 15 seconds) during whole listening state even if it has known itself not a root switch?

2.) What is exactly the BPDU propagated? For example, given a topology below

dddddd.png

2.1) Does A generate 2 different BPDU? (one with port id "eth1/1" and the other one with port id"eth1/2")?

2.2) If so, will C/D/E receive two different BPDU of A?

2.3) Assume A is the root switch, and D is also aware of that. How does D know the cost to root switch and put it into BPDU? 

17 REPLIES 17


My second and recent test looks better. Sw A , Root sw, shows that got 3 BPDUs from neighboring switches. while sending BPDUs out at the same time.
This makes sense since Root elections and DP/RP port elections are happening at the boot.

Hi Martin,

It sounds good and reasonable. Thanks for your full support.


forgot to attach doc, see attached