At 02:45 PM 2/27/02, Pierre-Alex Guanel wrote: >Priscilla, > >In the attachment (Cisco CCNA Exam Guide #640-507 Certification Guide: ISBN >0-7357-0971-8), page 167 - 168, the authors seem to indicate that CBPDUs are >sent from blocked ports!
They are talking about a network in transition. When a port transitions from blocking to listening, then it sends Configuration BPDUs. >The ability for CBPDUs to be sent out of blocked >port seems to a determinant factor for the Spanning Tree to be recomputed >after a topology change .... No, that's not true. >Here is a word by word copy of the passage. The part I have problem about is >the one with (!!!!!!) > >Thanks! > >Pierre-Alex > >--(e0)Bridge-1 (e1)-- (e0)Bridge 5(e1)---(e1) Bridge 4 (e0)---(e1)Bridge 3 >(e0)---(e1)Bridge 2 (e0)---> (To bridge 1 e0) > >Cost advertised by B2 is 100 >Cost advertised by B3 is 200 >Cost advertised by B5 is 10 >Blocked port: Bridge 3, port e1 > >Bridge 5's E1 port fails...Only Bridge 4's MaxAge expires. The other bridges >are still receiving CBPDUs on their root ports. After MaxAge expires, Bridge >4 will decide the following: > >Step 1 My E1 port is no longer my root port >Step 2 The same root bridge is being advertised in a CBPDU on my E0 port >(!!!!!) It should say "The same root bridge is being advertised in a Configuration BPDU that I'm sending on my E0 port." >Step 3 No other CBPDUs are being received >Step 4 My best path (and the only path, in this case) to the root is out of >my E0 port; therefore, my root port is now E0.) >Step 5 Because no other CBPDUs are entering my E1 port, I must be the >designated bridge on that segment. So, I will start sending CBPDUs on E1, That's right. E1 wasn't blocked and still isn't blocked. >adding my E0 port cost (10) to the cost of the CBPDU received in the CBPDU >entering E0 (200) for a total of 210 (!!!!!!) It depends on the timing. At some point B3 will start sending Configuration BPDUs. But not right away, I agree. (certainly not while it's still blocking.) > >>>>> > > >Kind Regards, > >Pierre-Alex ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=36722&t=36559 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
