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

UPLINKFAST

•  Uplinkfast automatically transform the state of alternate port( blocked to forward )and become root port, with out completing listening & learning state(because patch is already calculated as loop free path).
• Work only when failure of directly connected link.
• After making alternative port to root port
• spoof the CAM table from the new root port
• Does not apply at Core layer, apply at distributed & access layer
• due to the increase in cost & priority

PortFast

• PortFast doesnt disable STP on edge ports.
• Only put in blocked state
• Only send BPDU, doesnt recive BPDU
• Edge ports not subject to forward delay
• Not generate TCN (so no flush of CAM table, it cuts down the unknown unicast flooding in network) 
• 
  
• spanning-tree portfast default
• if enable portfast globally, every access port interfaces become portfast enabled port but not on trunk links
• some times there is a situation, enable portfast on trunk links also
• at that time use spanning-tree portfast trunk cmd used.
• If portfast enabled globally, when access port receive bpdu, it losses the portfast state and complete the listening & learning states then go to forwarding state
• But if portfast enable at interface level, port will remain in portfast state regardless of bpdu receive.
• show spanning-tree int e0/0 portfast

STP Terms

BRIDGE: 

• STP is oldest protocol
• at that time no switches(or may be switches are called bridges), so throughout STP, Switch is called as Bridge.

Root Bridge:

• Instead of broadcast, all bridges are elected one bridge as Root,
• then send information to that root bridge, root will send to destination
• Other than root bridge remaining all are called Designated Bridges

Root Port:

• Present on designated bridge
• By using this port only Designated Bridges connect to Root Bridge, 
• Remaining ports are Alternative Ports which are in blocked state.
• Any time only one Root Port per switch towards Root Bridge

Designated Port:

• Present on both Root & Designated Bridge
• Designated Port is a Port which is connected to Root port, 
• It sends information away from Root Bridge

Path Cost:

• Based on path cost we will elect the Root/Designated Port.
• Path Cost  is numerical value, 
• Based on the type of connecting media (Fast Ethernet, gigabit Ethernet, etc) path cast value will be changed

Data rate	STP Cost (802.1D-1998)	RSTP Cost (802.1D-2004 / 802.1w)
4 Mbit/s	250	5,000,000
10 Mbit/s	100	2,000,000
16 Mbit/s	62	1,250,000
100 Mbit/s	19	200,000
1 Gbit/s	4	20,000
2 Gbit/s	3	10,000
10 Gbit/s	2	2,000

Source: wikipedia

Spanning Tree Protocol

STP:

• Root Bridge Election
• Elect one Root Port per bridge
• Elect Designated Ports on Root bridge

Root Bridge Election:

• Based on Bridge ID of Switch
• ID contain:
• Bridge Priority (0-61440, increment of 4094)
• System ID ( VLAN no.)
• MAC Add (become Spanning Tree MAC address)
• Lowest Bridge ID containing Switch become Root Bridge

Manual Selection of Root Bridge:

• spanning-tree vlan [ids] priority         (lowest priority number will become root bridge)
• spanning-tree vlan [ids] root [primary|secondary]
•  without giving any priority value switch become root bridge
• by automatically decrease the priority value than current root bridge

Root bridge verification:

• show spanning-tree root
• show spanning-tree vlan [id]

ADDITIONAL:

it repeatedly looks for the optimal solution, selecting an “optimal” candidate every time.