Hi Rene/Laz,
Same question here, is this can only be used in case of indirect link failure?
Q2 ) As per topology used to describe this topic, If link b/w SW3 and SW1 get failed rather than SW3 and SW2 then will this still act as a indirect link failure ?
Hello Pradyumna
Backbonefast, like Uplinkfast, is used in case of an indirect link failure. However, this indirect link failure does not only have to occur on a link connected to the root bridge, it can take place anywhere on the network.
It depends on the “point of view”. For SW3, a failure of the SW1-SW2 link is an indirect link failure. In other words it doesn’t occur on one of its ports. For SW2, a failure of the SW1-SW3 link is an indirect link failure, because the failure doesn’t occur on one of its ports.
I hope this has been helpful!
Laz
Una duda en relación con esta parte del texto.
SW3 recibirá estas BPDU de SW2 pero se dará cuenta de que esta nueva BPDU es inferior en comparación con la anterior que tiene actualmente almacenada en su interfaz fa0 / 16 e ignorará esta nueva BPDU . Cuando un conmutador recibe una BPDU inferior, significa que el conmutador vecino ha perdido su conexión con el puente raíz.
CONSULTA:
1- Si el SW3 recibiera una BPDU superior del SW2,
¿ El SW3 la guardaría para esa interfaz, en lugar de descartarla?¿ la interfaz f0/16 pasaría directamente al estado listening, sin esperar los 20 sg?
2-¿Que implicaría que el SW3 recibiera una BPDU superior, en términos de cambio de topología?.
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English Translation:
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A doubt in relation to this part of the text.
SW3 will receive these BPDUs from SW2 but will realize that this new BPDU is inferior compared to the old one currently stored on its fa0 / 16 interface and will ignore this new BPDU. When a switch receives a lower BPDU, it means that the neighboring switch has lost its connection to the root bridge.
QUERY:
1- If SW3 receives a higher BPDU from SW2,
Would SW3 save it for that interface, instead of discarding it? Would the f0 / 16 interface go directly to the listening state, without waiting for the 20s?
2-What would it imply that SW3 received a higher BPDU, in terms of topology change?
Hello Julio
If SW3 received a BPDU from SW2 that is superior, then it would have to make the Fa0/16 the root port, and make Fa0/14 a designated port. In this case, both Fa0/16 and Fa0/14 would go directly into the listening state and go through the various states. They would not wait for 20 seconds of the max age timer. But in the scenario we are looking at here, SW1 is still root bridge, and the BPDU from SW2 is not superior, so it is discarded.
Remember that the max age timer is the maximum amount of time that a BPDU is valid for. So from the moment that SW2 starts sending BPDUs to SW3, and SW3 discards them, the last valid BPDU before the link failure expires after the 20 seconds of the max age timer. Only then will the blocked port go into the listening state.
If SW3 received a superior BPDU from SW2, then this means that SW2 should become the root bridge of this topology, and not SW1. But this would not happen at the same time as a link failure. If this was the case, it would have been so even before the link failure.
I hope this has been helpful!
Laz