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Spanning tree protocol
STP (Spanning Tree Protocol) prevents loops in networks with multiple connected switches by using the IEEE 802.1D standard and BPDUs to manage port states. It establishes a root bridge based on the lowest bridge ID and assigns port roles (designated, root, non-designated, and disabled) to maintain a loop-free topology. Five port states (blocking, listening, learning, forwarding, and disabled) guide STP's operation, each with specific timing and functional criteria for handling data frames.
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Spanning tree protocol
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- 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 DesignatedPort Root Port Non Designated (Blocked) Port Disabled Port
- 5. Designated Port Designatedport 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 Rootport 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 Disableport 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 Thisinformation 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 introducefive port states Blocking Listening Learning Forwarding Disabled
- 11. Blocking State Theport 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 Inthis 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. “ ” Thanks…. Credits • https://www.youtube.com/channel/UCb8pwZvymO1mMIXUbwuyHQg (for Video) •https://www.youtube.com/watch?v=pgpmOoLl_r4 (STP Concept)