Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
New Member

STP sending BPDU and loops

Hello

Few questions about STP:

1.Does access-ports take part in STP ? Does switch send BPDU on access port ? (let's assume tha portfast is disabled)

2. What will happen if i will connect SW1 and SW2 with two links and each port on each side of the link will be the access mode and same vlan number ?

Thanx

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: STP sending BPDU and loops

1) Yes access ports take part in STP even with portfast

2) One of the links will have to block.

Jon

6 REPLIES
Hall of Fame Super Blue

Re: STP sending BPDU and loops

1) Yes access ports take part in STP even with portfast

2) One of the links will have to block.

Jon

Blue

Re: STP sending BPDU and loops

Jon:

Can you elaborate on point 1?

Victor

Hall of Fame Super Blue

Re: STP sending BPDU and loops

Victor

Portfast allows a port to transmission straight to forwarding ie. no listening/learning stages. But it does not actually disable STP on that port. Of course if the device connecting to a portfast port does create a loop then it is usually too late to stop it because you have gone straight to forwarding but i just wanted to emphasise that portfast does not disable STP as some people think.

Jon

Blue

Re: STP sending BPDU and loops

Hey, Jon:

Yes, I know you are 100% correct. I just wanted to see what your perspective on this was.

In fact, because STP is running, even on a PortFast port, you really should enable BPDU guard on it to avoid the case in which some knucklehead plugs a switch into the port. Once the BPDU is received, the PortFast port will transition to errdisable.

Hall of Fame Super Blue

Re: STP sending BPDU and loops

Yep, I agree, BPDUGuard should be enabled on portfast ports as an extra safeguard.

And if you want to be really safe you should look at port security as well as BPDUGuard won't protect against hubs which don't send BPDUs.

But you know all this :-)

Jon

Blue

Re: STP sending BPDU and loops

Jon, I really didnt need any information from you...I confess, I was just flirting....you British stud. LOL

170
Views
0
Helpful
6
Replies
CreatePlease to create content