03-07-2016 06:26 AM - edited 03-08-2019 04:51 AM
Regarding TCN propagation towards the root switch, why shouldn't the switch sensing the topology change update directly all other switches in the STP instance.
What is the logic behind sending TCN upstream towards the root switch and root switch in turn helps in enabling TCAM updation of all other switches.
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03-08-2016 01:19 AM
Dear friends,
Please allow me to join.
To understand the motivation behind the two-phase TCN process in the 802.1D legacy STP, recall that:
RSTP significantly changed the rules on originating and accepting BPDUs, so its behavior is strongly different. The rules above apply only to legacy 802.1D STP.
Best regards,
Peter
03-07-2016 07:24 AM
I understand thats the reason RSTP came in to picture :)
But it came up with a handshake mechanism to avoid any temporary loops during convergence, which STP does not have by design.
Hope this helps
03-07-2016 12:51 PM
Hello,
I understand this is because the same reason the DR is elected in OSPF access networks, to have an organized communication, if the BPDUs had to traverse the whole network then there would be even more problems of network downs because of STP instability than we have now.
Root Bridge can send the BPDUs easily reaching every switch in the topology via the root port.
Hope this was not really confusing.
BR.
JC
03-08-2016 01:19 AM
Dear friends,
Please allow me to join.
To understand the motivation behind the two-phase TCN process in the 802.1D legacy STP, recall that:
RSTP significantly changed the rules on originating and accepting BPDUs, so its behavior is strongly different. The rules above apply only to legacy 802.1D STP.
Best regards,
Peter
03-08-2016 06:00 AM
Thank you Peter for the detailed clarification. I completely understand the logic behind that behaviour.
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