Free CCNA | Spanning Tree Protocol (Part 2) | Day 21 | CCNA 200-301 Complete Course

Welcome to Jeremy’s IT Lab

In this section, Jeremy introduces his IT Lab and the free CCNA course. He encourages viewers to subscribe, like, comment, and share the videos. The focus of this video is on spanning tree.

Introduction

• Jeremy welcomes viewers to his IT Lab and the free CCNA course.

• He requests viewers to subscribe, like, comment, and share the videos.

Spanning Tree Part 1 Recap

This section provides a recap of part 1 of the spanning tree topic.

Recap

• Part 1 focused on the basic purpose of spanning tree and how to calculate a spanning tree topology.

Spanning Tree States and Timers

This section discusses the different states and timers in spanning tree.

Spanning Tree States

• There are four states in spanning tree: blocking, forwarding, listening, and learning.

• Blocking and forwarding are stable states.

• Listening and learning are transitional states.

Spanning Tree Timers

• Timers determine when switches move between each state.

• The BPDU (bridge protocol data unit) contains fields that determine these timers.

Optional Features of STP

This section explores optional features or tools that can enhance spanning tree protocol (STP).

Optional Features

• There are additional features known as the "spanning tree toolkit" that can be enabled to improve STP.

Spanning Tree Configurations

This section covers configurations related to spanning tree.

Default Configuration

• Spanning tree runs by default without any configuration required.

Changing Root Switch

• It is important to know how to change which switch becomes the root switch for better traffic flow.

Practice Question and ExSim

This section introduces a practice question from Boson Software's ExSim, a recommended set of practice exams for CCNA preparation.

ExSim Practice Exams

• Boson Software's ExSim is highly regarded as the best practice exams for CCNA.

• It is an essential tool for preparing for the CCNA certification.

• Jeremy personally recommends using ExSim to pass CCNA and CCNP exams on the first try.

Spanning Tree Port States

This section explains the different port states in spanning tree.

Port States

• There are four port states: blocking, listening, learning, and forwarding.

• Blocking and forwarding are stable states.

• Listening and learning are transitional states.

Blocking State

This section focuses on the blocking state in spanning tree.

Blocking State

• Non-designated ports are in a blocking state to prevent loops.

• Interfaces in a blocking state do not send/receive regular network traffic but receive STP BPDUs (bridge protocol data units).

• They do not learn MAC addresses from regular traffic.

Listening State

This section discusses the listening state in spanning tree.

Listening State

• Designated or root ports enter the listening state.

• Non-designated ports remain in the blocking state.

• The listening state lasts for 15 seconds by default.

Learning State

This section covers the learning state in spanning tree.

Learning State

• Learning is a transitional state that leads to the forwarding state.

• Only designated or root ports enter the learning state.

Conclusion

This summary provides an overview of Jeremy's IT Lab video on spanning tree. It covers the purpose of spanning tree, its operation, states and timers, optional features, configurations, and port states. The video also introduces Boson Software's ExSim practice exams for CCNA preparation.

New Section

This section explains the default duration of the Learning state in Spanning Tree Protocol and how it is determined by the Forward delay timer.

The Learning State

• The Learning state is 15 seconds long by default, determined by the Forward delay timer.

• The same timer is used for both the Listening and Learning states, taking a total of 30 seconds to move through both states and enter a forwarding state.

• In the Learning state, an interface learns MAC addresses from regular traffic that arrives on it, preparing to forward traffic by building up its MAC address table.

New Section

This section highlights the similarities and differences between the Listening and Learning states in Spanning Tree Protocol.

Similarities and Differences

• An interface in both the Listening and Learning states only sends or receives spanning tree protocol BPDUs.

• However, in the Learning state, an interface also learns MAC addresses from regular traffic that arrives on it, adding them to its MAC address table.

New Section

This section focuses on the Forwarding state in Spanning Tree Protocol and how root and designated ports operate in this state.

The Forwarding State

• Root and Designated ports are in a Forwarding state when they are stable.

• A port in the Forwarding state operates as normal, sending/receiving BPDUs and normal traffic.

• It continues to learn MAC addresses from frames that arrive on it, adding them to its MAC address table.

New Section

This section provides a summary of each spanning tree port state and introduces the Disabled state for administratively disabled interfaces.

Summary of Port States

• Disabled state is the spanning tree state of a shutdown, administratively disabled interface.

• Review the table provided in the video for a summary of each spanning tree port state.

New Section

This section encourages viewers to review the provided table and flashcard deck for further study.

Review and Flashcards

• Pause the video to review the table summarizing each spanning tree port state.

• Download the flashcard deck from the link in the video description for additional review.

New Section

This section introduces and explains additional timers used in Spanning Tree Protocol, including Hello, Forward Delay, and Max Age timers.

Timers Used in Spanning Tree

• The Hello timer determines how often the root bridge sends hello BPDUs, typically every 2 seconds.

• Other switches forward received BPDUs but do not originate their own.

• BPDUs are only forwarded on designated ports.

New Section

This section provides more details about how BPDUs are forwarded and updates information between switches.

Forwarding BPDUs

• Once network convergence occurs, only the root bridge sends BPDUs.

• Other switches forward these BPDUs on their designated ports, updating information like bridge root cost, bridge ID, port ID, etc.

• The process repeats every two seconds as new BPDUs are sent by the root bridge.

New Section

This section explains how interfaces wait for BPDUs using the Max Age timer and what happens when they cease to receive them.

Max Age Timer

• The Max Age timer indicates how long an interface waits to change the spanning tree topology after not receiving BPDUs.

• Root ports and non-designated ports expect to receive BPDUs, which are forwarded by other switches.

• If a failure occurs and an interface no longer receives BPDUs, the Max Age timer counts down until it reaches 0.

New Section

This section continues explaining the behavior of the Max Age timer when BPDUs are not received on an interface.

Max Age Timer (Continued)

• If another BPDU is received before the Max Age timer reaches 0, the timer resets to 20 seconds and no changes occur.

• If no additional BPDU is received, the switch reevaluates its STP choices, including root bridge and port roles.

• A non-designated port selected as designated or root port transitions from blocking to listening state, then learning state, and finally forwarding state. This transition takes a total of 50 seconds.

New Section

This section explains the duration of Listening and Learning states during forwarding transitions in Spanning Tree Protocol.

Forward Delay Timer

• The Forward delay timer determines the length of each transitional state (Listening and Learning) that a port goes through when moving to forwarding.

• With a default Forward delay timer of 15 seconds, it takes a total of 30 seconds for a switchport to move through both states and forward traffic.

New Section

This section introduces the concept of the max age timer and its role in determining when interfaces change their spanning tree topology.

Max Age Timer (Continued)

• The max age timer indicates how long an interface waits to change the spanning tree topology after ceasing to receive BPDUs.

• Each collision domain has one designated port, and BPDUs are forwarded out of designated ports.

• If a failure occurs and an interface no longer receives BPDUs, the max age timer counts down until it reaches 0.

New Section

This section provides an example scenario to demonstrate the behavior of the max age timer when BPDUs are not received on an interface.

Max Age Timer Example

• The root bridge sends BPDUs, which are forwarded by other switches.

• If a switch's interface receives a BPDU, the max age timer is reset. If not, it continues counting down.

• In case of a failure where an interface no longer receives BPDUs, the max age timer counts down until it reaches 0.

New Section

This section explains what happens when the max age timer reaches 0 and how interfaces reevaluate their STP choices.

Max Age Timer Conclusion

• When the max age timer reaches 0 without receiving another BPDU, interfaces reevaluate their STP choices.

• Non-designated ports may transition from blocking state to listening state, learning state, and finally forwarding state.

• It can take up to 50 seconds for a blocking interface to transition to forwarding due to these timers and transitional states.

New Section

This section concludes by summarizing why timers and transitional states exist in Spanning Tree Protocol.

Purpose of Timers and Transitional States

• Timers and transitional states ensure that loops aren't accidentally created in Spanning Tree Protocol.

New Section

This section discusses the process of creating a loop by blocking an interface and introduces the spanning tree BPDU (Bridge Protocol Data Unit).

Creating a Loop and Spanning Tree BPDU

• A blocking interface cannot move directly to forwarding state; it must go through the listening and learning states.

• Cisco's PVST+ uses the destination MAC address 0100.0ccc.cccd for its BPDUs.

• PVST is an older version that only supports Cisco's ISL for trunk encapsulation, while PVST+ is a newer version that supports dot1q.

• Regular spanning tree uses a destination MAC address of 0180.c200.0000.

• The BPDU (Bridge Protocol Data Unit) includes fields such as protocol identifier, protocol version identifier, and BPDU type.

• Flags in the BPDU are used to signal topology changes to other switches.

• The root identifier field contains information about the bridge priority, extended system ID (VLAN ID), and bridge system ID (MAC Address of the root bridge).

• The root path cost indicates whether a switch is the root bridge or not.

• The port identifier field specifies which interface sent the BPDU.

• Timers in the BPDU include message age, max age, hello, and forward delay.

New Section

This section provides additional details about timers in spanning tree and introduces optional features called "spanning tree toolkit."

Timers and Optional Features

• Message age starts at 0 at the root bridge and increases by 1 each time it is forwarded by another switch. It is subtracted from the max age when a switch receives the BPDU.

• Max age, hello, and forward delay are three timers used in spanning tree protocol.

• Spanning tree timers on the root bridge determine the timers for the rest of the switches in the network.

• Optional features, known as the spanning tree toolkit, can be enabled to improve the functionality of spanning tree protocol.

• Portfast is one such feature that can be enabled on interfaces connected to end hosts. It allows designated ports to bypass the listening and learning states, reducing the time it takes for them to start forwarding traffic.

New Section

This section explains why spanning tree goes through a process before putting a port in the forwarding state and clarifies that only interfaces connected to another switch can form a Layer 2 loop.

Spanning Tree Process and Layer 2 Loops

• Spanning tree goes through the listening and learning states before putting a port in the forwarding state to ensure no Layer 2 loops are formed.

• Interfaces connected to end hosts must go through 15 seconds of listening and 15 seconds of learning before they can start forwarding traffic.

• A little experiment is suggested using Packet Tracer to observe how link lights change during this process.

• The link light on a switch will initially be orange when an interface is not yet in the forwarding state but going through listening and learning states. After 30 seconds, it should turn green indicating that it is finally forwarding traffic.

• Only interfaces connected to another switch have the potential to form a Layer 2 loop.

The transcript provided does not include any further sections or timestamps beyond this point.

New Section

This section discusses the use of spanning tree in network configurations and introduces the concept of portfast and its potential risks.

Spanning Tree and Portfast

• Spanning tree must be enabled only on ports connected to end hosts to avoid causing a Layer 2 loop when connected to another switch. Listening and learning states help prevent loops.

• Portfast is enabled at the interface level using the command SPANNING-TREE PORTFAST. It allows for quick connection of switchports to end hosts without waiting for 30 seconds.

• Portfast should only be enabled on access ports, not trunk ports that are typically connected to other switches.

• The command spanning-tree portfast default enables portfast on all access ports but not trunk ports.

• Portfast can lead to Layer 2 loops if an employee unknowingly connects another switch or if network cabling is changed without caution.

New Section

This section explains how to enable portfast and introduces BPDU Guard as a protection against loops caused by portfast.

Enabling Portfast and BPDU Guard

• Portfast can be enabled at the interface level with the command spanning-tree portfast.

• A warning message emphasizes that portfast should only be enabled on ports connected to end hosts, not trunk ports.

• The command spanning-tree bpduguard enable configures BPDU Guard on an interface with the purpose of preventing loops caused by receiving BPDUs from other switches.

• The command spanning-tree portfast bpduguard default enables BPDU Guard on all portfast-enabled interfaces.

New Section

This section demonstrates how BPDU Guard disables a port upon receiving a BPDU from another switch.

BPDU Guard in Action

• When a BPDU arrives on a port with BPDU Guard enabled, the port is disabled to prevent loop formation.

• To re-enable a port that was disabled by BPDU Guard, use the commands shutdown and then no shutdown.

• If the problem causing the BPDU arrival is not resolved, the interface will be immediately disabled again upon receiving the next BPDU.

New Section

This section mentions additional optional spanning tree features such as Root Guard and Loop Guard.

Additional Spanning Tree Features

• Root Guard prevents a switch from accepting a new switch as the root bridge even if it receives a superior BPDU on an interface. The interface will be disabled.

• Loop Guard prevents forwarding on an interface even if it stops receiving BPDUs. The interface will be disabled.

• While these features are mentioned, they may not be required knowledge for the CCNA exam.

New Section

This section emphasizes knowing Portfast and BPDU Guard for the CCNA exam and briefly introduces two other optional spanning tree features: Root Guard and Loop Guard.

Importance of Portfast and BPDU Guard

• Portfast and BPDU Guard are important concepts to understand for the CCNA exam.

• Other optional spanning tree features like Root Guard and Loop Guard exist but may not be necessary knowledge for the exam.

• It is recommended to search online for more information about these optional features if desired.

New Section

This section explains how to configure spanning tree mode on switches.

Configuring Spanning Tree Mode

• The command spanning-tree mode allows configuring the spanning mode used by switches.

• There are three options available for spanning tree mode configuration.

New Section

In this section, the speaker discusses how to enable and configure the root bridge in a spanning tree network.

Enabling Classic Spanning Tree

• To enable classic spanning tree for a lab, use the command SPANNING-TREE MODE PVST.

• The root bridge can be manually configured by manipulating the bridge priority of a switch.

• By default, SW1 is the root bridge in the given topology.

Configuring Root Bridge

• SW3 can be configured as the root bridge by using the command SPANNING-TREE VLAN <vlan number> ROOT PRIMARY.

• This sets the STP priority to 24576 and makes SW3 the root bridge.

• The command SPANNING-TREE VLAN <vlan number> ROOT SECONDARY can be used to configure a secondary root bridge with a priority of 28672.

New Section

In this section, we learn about configuring primary and secondary root bridges in a spanning tree network.

Configuring Primary Root Bridge

• The command SPANNING-TREE VLAN <vlan number> ROOT PRIMARY sets the switch as the primary root bridge for that VLAN.

• The actual command applied is SPANNING-TREE VLAN <vlan number> PRIORITY 24576.

Configuring Secondary Root Bridge

• The command SPANNING-TREE VLAN <vlan number> ROOT SECONDARY sets the switch as the secondary root bridge for that VLAN.

• The actual command applied is SPANNING-TREE VLAN <vlan number> PRIORITY 28672.

New Section

This section covers load balancing in spanning tree networks and how different interfaces are disabled based on VLAN configurations.

Load Balancing and Interface Blocking

• Spanning tree load balancing allows for efficient utilization of interface bandwidth.

• In a network with multiple VLANs, blocking the same interface in each VLAN is wasteful.

• By configuring different root bridges for different VLANs, different interfaces can be disabled based on the VLAN configuration.

New Section

This section presents a quiz question related to configuring primary and secondary root bridges for different VLANs.

Quiz Question: Configuring Primary and Secondary Root Bridges

• Two VLANs (10 and 20) are active in the network.

• SW3 is the default root bridge for both VLANs.

• The task is to configure SW1 as the primary root bridge for VLAN10 and the secondary root bridge for VLAN20, and vice versa for SW2.

• The commands spanning-tree root should be used to configure the switches accordingly.

New Section

This section concludes the discussion on configuring primary and secondary root bridges and introduces spanning-tree port settings.

Configuring Primary and Secondary Root Bridges (Continued)

• SW1 should be configured as the primary root bridge for VLAN10 and secondary root bridge for VLAN20 using specific spanning-tree root commands.

• SW2 should be configured as the primary root bridge for VLAN20 and secondary root bridge for VLAN10 using specific spanning-tree root commands.

Load Balancing Across Interfaces

• Load balancing in spanning tree networks ensures that different connections are used in different VLANs, distributing the load across interfaces.

New Section

This section covers spanning-tree port settings, including cost and port priority configurations.

Spanning Tree Port Settings

• Two main settings can be configured on a spanning tree port: cost and port priority.

• Both settings are configured on a per-VLAN basis, similar to bridge priority configuration.

• The cost represents the root cost and determines the path selection in spanning tree networks.

New Section

In this section, the instructor discusses the reasons for changing values related to root port and designated port selection process. The range of cost and port-priority settings for spanning tree interfaces is also explained.

Changing Root Port and Designated Port Selection Process

• To change the result of the root port or designated port selection process.

• Configuring the cost of an interface (range from 1 to 200 million).

• Setting the port-priority (increments of 32, from 0 to 224).

New Section

This section covers the essential spanning tree interface settings required for CCNA certification. The lab video will provide practical examples to reinforce these concepts.

Spanning Tree Interface Settings

• Cost configuration range from 1 to 200 million.

• Port-priority configuration range from 0 to 224.

• Lab video practice recommended for hands-on experience.

New Section

This section summarizes various topics covered in relation to spanning tree, including states, timers, BPDU structure, and optional features like portfast and BPDU guard. Basic configurations such as setting up a root bridge and load balancing across different VLANs are also discussed.

Summary of Topics Covered

• Different spanning tree states and timers used.

• Structure of a spanning tree BPDU.

• Optional features like portfast and BPDU guard.

• Basic configurations including root bridge setup and load balancing across VLANs.

New Section

This section introduces a quiz with three questions related to spanning tree concepts covered in the video. Additionally, one practice question from Boson Software's ExSim for CCNA is presented.

Quiz Questions on Spanning Tree

• Three quiz questions covering spanning tree concepts.

• One practice question from Boson Software's ExSim for CCNA.

New Section

This section presents a quiz question regarding network connectivity issues and possible solutions related to spanning tree.

Quiz Question: Network Connectivity Issue

• Scenario: Unable to connect to the network for half a minute after connecting a PC to a switch.

• Two options that could fix the issue and allow quicker network access (choose two):

• Enable portfast on the switch port connected to the PC (Answer A).

• Reduce the STP forward delay timer (Answer C).

New Section

This section provides explanations for the correct answers of the previous quiz question, emphasizing the benefits of using portfast and adjusting STP timers.

Explanation of Correct Answers

• Answer A (Enable portfast): Allows switchports to bypass listening and learning states, providing immediate forwarding state after connecting a PC.

• Answer C (Reduce forward delay timer): Shortening this timer enables quicker transition from listening and learning states to forwarding state.

New Section

This section presents another quiz question related to STP port priority identification based on packet capture analysis.

Quiz Question: STP Port Priority Identification

• Scenario: Packet capture indicates an STP port ID of 0x8002.

• The correct answer is C, indicating an STP port priority of 128. The hexadecimal value "8 0" corresponds to decimal 128.

New Section

This section introduces a quiz question about preventing Layer 2 loops when connecting switches together.

Quiz Question: Preventing Layer 2 Loops

• Scenario: Preventing Layer 2 loops when a user connects a switch to a switch port.

• The correct answer is D, using BPDU guard as the spanning tree optional feature.

New Section

This section presents a practice question from Boson ExSim for CCNA, focusing on reducing forwarding time for switch ports.

Practice Question from Boson ExSim

• Scenario: Decreasing the time it takes for switch ports on SwitchA to begin forwarding.

• The correct answer is D, indicating that all access ports on SwitchA will use PortFast.

New Section

This section provides an explanation of the correct answer for the previous practice question and highlights the benefits of enabling PortFast on access ports.

Explanation of Correct Answer

• All access ports on SwitchA will use PortFast to enable faster connectivity for hosts.

• Without PortFast, switch ports transition through STP listening and learning states before entering the forwarding state.

New Section

This section emphasizes the importance of explanations provided by Boson ExSim practice exams and their usefulness in understanding correct answers.

Importance of Explanations in Practice Exams

• Boson ExSim provides detailed explanations for correct and incorrect answers.

• Understanding why an answer is correct or incorrect enhances learning experience.

STP Listening and Learning States

This section discusses the STP (Spanning Tree Protocol) listening and learning states. It also provides references to additional resources for further study.

STP Listening and Learning States

• The video recommends the official cert guide by Wendell Odom as a valuable resource for understanding STP states.

• Cisco documentation is also suggested for free online reading.

• Boson ExSim practice exams are highly recommended, as they were used by the speaker for their CCNA and CCNP certifications. A link to access these practice exams is provided in the video description.

Supplementary Materials and Practice Lab

This section highlights supplementary materials available for this video, including a review flashcard deck and a packet tracer practice lab.

Supplementary Materials

• A review flashcard deck compatible with the software 'Anki' can be downloaded from the link provided in the video description.

• Additionally, there is a packet tracer practice lab that viewers are encouraged to try on their own. This lab offers further practice with the configurations covered in the video.

Acknowledgements

The speaker expresses gratitude towards JCNP-level channel members who have supported their work.

Acknowledgements

• The speaker thanks several individuals who are JCNP-level channel members, mentioning them by name.

• They express appreciation for their support and apologize if any names were mispronounced.

• The list of JCNP-level members mentioned was accurate as of May 17th, 2020. Viewers who signed up recently may not see their names listed but will be acknowledged in future videos.

Conclusion and Call to Action

The speaker concludes the video by thanking viewers for watching and encourages them to engage with the channel.

Conclusion and Call to Action

• Viewers are thanked for watching the video.

• The speaker requests viewers to subscribe to the channel, like the video, leave a comment, and share it with others.