06-16-2010 11:20 AM - edited 03-06-2019 11:36 AM
Hello
A port in the blocking state performs as follows:
When it says "Does not transmit BPDU's" does that mean just that specific switch is not transmitting, because there must be a switch sending out some sort of BPDU in order for the STP to be working right? I assume they are describing a switch alone by itself does not transmit anything. However if there was other switches already running STP successfully then it would transmit it's BPDU's to the new switch turned on?
Please advise.
Thanks.
Joe
Reference the following document for the source information: http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm
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06-16-2010 11:25 AM
When it says "Does not transmit BPDU's" does that mean just that specific switch is not transmitting, because there must be a switch sending out some sort of BPDU in order for the STP to be working right? I assume they are describing a switch alone by itself does not transmit anything. However if there was other switches already running STP successfully then it would transmit it's BPDU's to the new switch turned on?
Please advise.
Thanks.
Joe
Reference the following document for the source information: http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm
Joe
It is per port not per switch. So a port that is blocked receives but does not transmit BPDUs but there may well be other ports on the switch that are forwarding BPDUs.
Jon
06-16-2010 11:25 AM
When it says "Does not transmit BPDU's" does that mean just that specific switch is not transmitting, because there must be a switch sending out some sort of BPDU in order for the STP to be working right? I assume they are describing a switch alone by itself does not transmit anything. However if there was other switches already running STP successfully then it would transmit it's BPDU's to the new switch turned on?
Please advise.
Thanks.
Joe
Reference the following document for the source information: http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/sw_ntman/cwsimain/cwsi2/cwsiug2/vlan2/stpapp.htm
Joe
It is per port not per switch. So a port that is blocked receives but does not transmit BPDUs but there may well be other ports on the switch that are forwarding BPDUs.
Jon
06-16-2010 11:31 AM
Jon
Thank you very much
Joe
06-16-2010 01:35 PM
Adding to jon reply,
A port in STP blocking state relies on continous recieved BPDU, if the port for any reason failed to recieve those BPDUs , the port will immediately transit to STP forwarding state, hence causing spanning tree bridging loop.
A port in STP blocking state doesnt forward any BPDUs.
HTH
Mohamed
06-16-2010 01:47 PM
Mohamed, I'm certain that a port in blocking state does not immediately transition to forwarding state when it stops receiving BPDUs. It waits for timers to expire, those of which I can't recall off the top of my head (max age, 2x forward delay?), which is about 50 seconds.
Good ways to get around the STP convergence time would be to switch to RSTP, or use Uplink fast on the access layer which has <5 second convergence time and brings up the blocked port immediately.
06-16-2010 02:00 PM
Yes nelson you are correct, I should have mentioned that.
yes for STP 802.1d, it waits for max age timer 20 sec + 2 x 15 sec forward delay timer which is 50 sec.
HTH
Mohamed
06-17-2010 11:05 PM
Thank you everyone for your responses -
I think all your information is extremely helpful and have given everyone the five stars!
Thanks again... you all are great ---
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