BACKBONEFAST

• Not fast as uplinkfast due to link failure at some where else at upstream of root port 
• Indirect failure, start recalculate stp
• i.e. there is a problem at upstream of root port and root bridge is not reachable.
• After a failure of upstream, upstream bridge advertise inferior BPDU(worse cost to root) to root port.
• send Root Link Query(specific for BackBoneFast & ask Do u have alternate path)  
• then root port containing bridge understand there is link failure to reach root bridge,
• and expires max-age time(defaultly 20sec) and recalculate path costs
• when baackbonefast is used time to reconverge is only the listen&learn time only, no max-age
• spanning tree backbonefast on global mode