Three switch chained together physically to form a loop network as this:A(1/1)-B(1/1)B(1/2)-C(1/2)C(1/1)-A(1-2). A(1/2)is in block mode and C is root bridge.
1.)Will A(1/2) receive BPDU from C? My understand is after convergence BPDU is always sent from root bridge to the down stream's root port, and so on.So will A(1/2) receive BPDU?
2) If link between B(1/2)-C(1/2) goes down, after 20ms(maxage), A goes into listening mode.Will A send BPDU trying to announce itself is a root bridge? Obiously C is still root bridge this moment.If A(1/2) was receiving BPDU via the blocked port all the time then I think A should not send BPDU. I am reading the Cisco LAN switch book(Kevin hammilton), however at this point I am a little bit lost.Thanks a lot.
BPDU's are always sent downstream orginiating from the Root Bridge. A(1/2) will continue to hear BPDU's so that switch A will know that that port can change state if A(1/1) is not functioning. In the book you are reading, take a look at chapter 6 Figure 6-9. This demonstrates it. If you have the same older version of the book as me, it will be on page 170.
OK. One more thing I am not clear is that on that book page 252 says if link A and B goes down, C won't receive BPDU from B for 20s until reaching max age. Somewhere else in this book says then C'1/1 goes to listening mode and send BPDU to announce itself is root. What I am confused is if A's 1/1 still keep receiving BPDU from A's 1/1. How should it anounce itself is root?
The way spanning tree works is that when a switch first comes on line, it will send out BPDU's announcing itself as root with the priority of 32768 (i think thats the right number, I dont have my book handy right now). It will continue to announce itself as root until it hears a better offer of lets say 32767. Now when it hears that BPDU, it knows there is a root bridge already elected and will discontinue the BPDU's. Now if any link were to go down that this switch is uplinked to, the election process will begin to find a new root bridge (if no configurations have been made than this should be the switch with the lowest mac address).
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...