This is Basic of STP. By that you can able to understand basics of Spanning Tree. ALSO THIS SLIDE IS JUST FOR KNOWLEDGE.

1. STP
Spanning Tree Protocol

2. What is STP???
 STP used to prevent from looping when switches or bridges are
connected to each other with multiple ports.
 STP implements open standard 802.1D IEEE algorithm by exchanging
BPDU (Bridge Protocol Data Unit) with other switches to detect loops
and remove the loop by shutting down the selected bridge interface.
 STA (Spanning Tree Algorithm) is used in this process and this
algorithm guarantees that only one path between two devices is
active.
 STP is enabled by default on all Cisco Switches.

3. How STP works???
 The working of BPDU is to make elections between switches and check
for lower Bridge ID
 Bridge ID= Priority + MAC address
 The switch with lower Bridge ID will be Root Bridge and other switches
will become not root bridge
 The port of root bridge will become Designated port and the port in
front of designated port is either called Root Port or Blocked Port
(depend on its cost and Switch ID)
 Then Blocked port will automatically off for prevent from loop with in
network

4. Port Roles
 Designated Port
 Root Port
 Non Designated (Blocked) Port
 Disabled Port

5. Designated Port
 Designated port exist on root switches as well as on non root switches
 Its working is to receive packet which is coming through root port
 Only one designated port is allowed per segment
 On root switch, all ports are designated port
 Designated port also populate MAC address on MAC table

6. Root Port
 Root port exist on non root switch and is the switch port with the best
path to the root bridge
 The working of root port is to forward packet toward root switch
 Root port also populate MAC address in MAC Table

7. Non Designated (Blocked) Port
 Non Designated port is a switch port that is blocked
 It is also called a blocked port or sometime alternate port
 It can not forward packets to next switch
 It can not populate MAC address in MAC table

8. Disabled Port
 Disable port is the port which is blocked by Network
Administrator
 It can not send packet to another switch
 Also it can not populate MAC address on MAC table
 A disable port is not a part of Spanning Tree process

9. Path Cost
 This information get by summing up the individual port
cost along the path from the destination to the root
bridge
 These are default path costs
 10 Gb/s have 2 cost
 1 Gb/s have 4 cost
 100 Mb/s have 19 cost
 10 Mb/s have 100 cost

10. Port States
STP introduce five port states
 Blocking
 Listening
 Learning
 Forwarding
 Disabled

11. Blocking State
 The port is a non designated port and does not participate in frame
forwarding
 Its time is 20 sec or unlimited
Listening State
 At this state switch is not only receive BPDU frame, it also send BPDU
frame to next switch, by that port is participating in active topology
 Its time is 15 sec

12. Learning State
 In this state Switch is populating MAC Address in MAC Table
 Its time is 15 sec
Forwarding State
 At this state port is forwarding and receiving BPDU frame and it is a
part of STP process
 Its time is unlimited
Disabled State
 This state does not participate in Spanning Tree process because port
is administratively disabled
 Its time is Unlimited

14. “
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Thanks….
Credits
• https://www.youtube.com/channel/UCb8pwZvymO1mMIXUbwuyHQg (for
Video)
• https://www.youtube.com/watch?v=pgpmOoLl_r4 (STP Concept)