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RSTP BPDU Question

I've been testing RSTP and on access ports where portfast is configured the switch continously sends BPDUs. Is this normal behavior? I don't see the reason why the switch needs to send out BPDUs every 2 seconds out every single access port.

Can someone please shed some light on this? I'm considering on filtering BPDUs on every access port.

debug spanning-tree bpdu transmit

29w1d: RSTP(102): sending BPDU out Fa2/11

29w1d: RSTP(102): sending BPDU out Fa2/13

29w1d: RSTP(102): sending BPDU out Fa2/1

29w1d: RSTP(102): sending BPDU out Fa2/8

29w1d: RSTP(102): sending BPDU out Fa2/10

29w1d: RSTP(102): sending BPDU out Fa2/11

29w1d: RSTP(102): sending BPDU out Fa2/13

3 REPLIES
Silver

Re: RSTP BPDU Question

This is normal behavior. Even the edge ports need to be protected from potential loops. If you disabled the sending of BPDUs from these ports, what would happen if one were connected to another switch? What if a user connected two ports on a hub to the switch? RSTP would not be able to detect the loop. The reception of a BPDU is a fundemental means by which a switch knows it has been connected to another switch and therefore needs to make STP considerations.

Please rate all helpful posts.

Regards,

Brad

New Member

Re: RSTP BPDU Question

Thanks for your reply. Maybe I'm not thinking all the way through on this.

I just didn't see this behavior with 802.1d while doing a debug. I saw it on the Trunk interfaces between switches but not on access-ports.

But in any case RSTP has made life a lot easier!

Thanks,

Bob.

Bronze

Re: RSTP BPDU Question

Portfast doesn't disable spanning tree. PortFast causes a spanning tree port to immediately enter the forwarding state, bypassing the listening and learning states. And as previlosly stated, BPDUs are still forwarded to protect against loops.

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