Spanning tree

Loop preventsion

Loop gaurd
BPDU filter
UDLD

Spanning tree

4 Flavors
802.1 d  Reg
802.1 Not Stand, PVST(only works with ISL) and PVST+(for 802.1q)  Both Cisco Only!
802.1 w Rapid
802.1 s MST

Port States
* Disable
* Blocking No Packets (frames) forwarded STP still monitoring BDPUs
* Listening Processing BDPUs
* Learning Learning mac addresses and building switching table
* Forwarding Port is forwarding and receives Packets (frames) STP monitors for BDPUs
^ 802.1w
^ discarding       - same as blocking
^ learning          - same as learning
^ Forwarding    - same as forwarding

Port Roles
 *root - the port the receives the best BPDU on a switch, from the root, the port "closest" to the root (root switches do not have root ports)
 *designated - the port that can sent the best BPDU on the segment. There can only be one des port on a segment
 * Non-designated ports are blocking port in 802.1d STP
^ in 802.1w
 ^ Alternate Port - receives more useful BPDU from the same switch it is on and is in blocking. An alternate port provides an alternate path to the root bridge and therefore can replace the root port if it fails.
 ^ Backup port - Is in blocking, and  provides redundant connectivity to the same segment and cannot guarantee an alternate connectivity to the root bridge.