PORT COST vs PORT PRIORITY

Both parameters are used to determine which interface will be in forwarding state.

They have differences though:

•  If you want to affect how to the local switch elects the root port change the cost on the links.  Cost is cumulative throughout the STP domain. The higher cost is the less preferred.
•  If you want to affect how downstream switch elects its root port change the priority. This is only local significant between the two directly connected switches. Highest priority is less preferred.

 Going away from the root of the tree use priority whereas, when going towards the root of the tree use cost.

Reff: https://supportforums.cisco.com/thread/16435

SPANNING TREE:
to check total path cost/priority between current designated bridge to root bridge:
show spann root [cost/priority]

To change root port(towards root bridge) use spanning-tree cost on desired port.
To change the root port on below directly connected designated bridge(which is away from root bridge), use spanning-tree priority on desired port which is place on present switch.
note: if u r confused about toward/away root bridge, avoid rackets in above and read again, then read below
 Ex:

• If A is root bridge, C is designated bridge reach the root bridge A via designated bridge B. 
• Now we want to change the root port on B, use spanning-tree cost command on B. 
• Like this u change the root port on C using cost command on C. 
• Spanning-tree Priority command case is different, if we want to change the root port on C, but not use on C instead used on B.

BPDU FILTER:

• config at interface level or globally
• both have same effect disable STP on per interface basis
• this can stop STP information at incoming/outgoing interface
• Used at access layer at which end host are users
• this block the stp information reaching the end hosts
• if know (root bridge, mac add, priority), there is possibility malfunction of STP
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