Spanning Tree Protocol Explained | Step by Step
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Spanning Tree Protocol / STP is a big topic on the CCNA exam. Many people struggle with STP so in this video, we try to break it down as much as possible. Spanning Tree follows a strict set of rules which when learnt, will allow you to answer any STP questions you get.
This video focus on the standard 802.1d (and PVST+) which is the original STP standard.
Election Process
1. Elect a Root Bridge
Switch with the lowest BID
2. Place all Root Bridge interfaces in to a Forwarding state
3. Each Non-Root switch elects a Root Port
Lowest cost
Lowest neighbour BID
Lowest neighbour port priority
Lowest neighbour port number
4. Elect a Designated Port
Lowest root cost
Lowest BID
Lowest neighbour port priority
Lowest neighbour port number
5. All other ports are placed in to a Blocking State
#ccna #cisco #networking
Just in case this is helpful for others, here are my notes from this video.
STP Overview
Spanning Tree Protocol
Types of STP
- Original STP
- STP / 802.1D
- PVST+
- Cisco improvement adding a per VLAN feature
- Cisco default
- RSTP / 802.1w
- Improved STP with much faster convergence
- Rapid PVST+
- Cisco improvement of RSTP adding per VLAN feature
- Makes a large network more efficient
Why STP?
- STP is used to prevent loops when using redundant switches
- Broadcast messages are sent all the time and Broadcast Storms are easy to trigger
- Loops also cause unstable MAC address tables because they're constantly being changed/updated
- Duplicate frames are being sent to the same host
How STP Works
- Switches in a loop 'drop' one of the ports
- Switch with the blocked port still receives the data but it ignores it
- Simple but how the switches choose the port to block can be tricky
Choosing the blocked port
- 1) Elect a root bridge
- King of switches
- 2) Place root bridge interfaces into a Forwarding state
- 3) Each non-root switch selects its Root Port
- This is the best route to the bridge
- 4) Remaining links choose a Designated Port
- 5) All other ports are put into a Blocking state
Roles
- Root Ports
- The best port to reach the Root Bridge
- Designated Port
- Port with the best route to the Root Bridge on a link
- Non-Designated Ports
- All other ports that are in a blocking state
States
- Disabled
- Port that is shutdown
- Blocking
- A port that is blocking traffic
- Must move to Listening state before moving to Forwarding
- Listening
- Not forwarding traffic and not learning MAC addresses
- Transitional State while changing from 1 role to another
- Held in this state for the Forward Delay timer (15 sec default)
- Learning
- Not forwarding traffic but learning MAC addresses
- Transitional State while changing from 1 role to another
- Held in this state for the Forward Delay timer (15 sec default)
- After this, the port can now move to a Forwarding state
- Forwarding
- Sending and receiving traffic like normal
- Can move directly to Blocking
Root Bridge Election
- Each switch has a BPDU. BPDU contains:
- Root Cost
- Cost of the root bridge
- BID (Bridge ID)
- The switch with the lowest overall BID will become the root bridge
- They look something like: 32769aaaa:aaaa:aaaa
- BID is made up of:
- STP priority
- Default value of 32768 + VLAN number
- For VLAN 1, the STP priority would be 32769
- MAC Address
- Each switch thinks it should be the root bridge
- They share their BPDUs with each other
- Once they all agree, the root bridge has been elected
- All ports on the root bridge enter a Forwarding State
- Each non-root switch will now choose the best path to the root bridge
- This is the Root Port
- This is based on Port Cost
- Cost is based on port speed
- Better speed, lower cost
- Each outgoing port to the root added together
- Can be set manually
- If a tie happens, they look at lowest neighbor BID
- If they tie, they use lowest neighbor port priority
- If they tie, lowest neighbor port number
- Select a Designated Port
- Look at lowest root cost to the bridge
- If that ties, lowest BID
- If that ties, lowest neighbor port priority
- If that ties, lowest neighbor port number
- Every port that is not a root port of designated port is put in a Blocking State
Downfall of STP -- Convergence
- The time it takes to do the work and become stable
Timers - Default (RSTP addresses the delay of convergence)
- Hello
- Every 2 seconds
- Lets everyone know everything is still alive
- MaxAge
- 10x Hello timer by default (20 seconds)
- The time the switch will wait before it realizes something is wrong
- Forward Delay
- 15 seconds
- The time between the Listening and Learning state
thanks a lot
Thanks sir
Thank you!
Much appreciated!
You are just the best! Thank you
I have never ever seen this kind of clear explanations... this is awesome... keep it up...
Thanks Dakshina!
minute 9.58(32768 or 32769)??@@Certbros
@@bardo4860 it's 32769. 32768+vlan. Default vlan is 1
@@bardo4860 I wondered too but below is an explanation
@@jeevankumar-mr6zn Thanks
Time: Your video was longer than other Spanning Tree informative videos but your video has more information. My time watching your video was time well spent.
Thanks man!
It's 0549 and its usually really quiet when I study this early in the morning, and the "Arrogant ****" came out of nowhere!! Educational and HILARIOUS, now I have to subscribe!
I was watching this video... and that comment got me like a curveball. He said it so straightforward yet out of nowhere.
it's reason why I'm subscribing, and why I'm in the comment section lol
This will forever be the best STP breakdown out there.
This is definitely the best explanation of STP I've ever watched. I feel like I actually know something more now instead of being more lost.
Thanks! Glad it helped!
the best explanation of STP on the internet
That will be written on my gravestone 😂
unexpected laugh at 10:04
HAHA! Thanks man!
That made me laugh so hard my headphones fell off at work lol
I laughed so hard at it XD
Much funnier I think is 12:28
Oh man, I so needed that after frying my brain today learning SPT for the first time. Thank you, sincerely.
This is the best and most straightforward breakdown of this topic I've ever seen. I was struggling even with the excellent Wendell book. I truly hope you continue making more videos like these! It's invaluable
Thanks! Working on the next lot
@@Certbros Mr can you please give me your phone number and your E mail because I have a question that I don't know how to solve it only one question
agreed with this. the book references illustrations on previous pages. doesnt help for people with ADD constantly flipping back and forth while trying to focus on the content lol
@@abdulrahmanismailali1064 Bruh......
You clarified this subject for me after I spent almost a week banging my head against the wall. Thank you so much. Thank you for the humorous *bleep* with the arrogant router comment. Made my day.
Good to hear it helped!
My God! I cannot believe I actually understood STP. I do not have a background in networking and have always struggled with understanding network concepts. I am very grateful to you for making these videos. Thank you and keep them coming!
Thanks Nikhil! Glad it helped you out.
This is one of the best Network Tech vids I've ever seen. Not only was each concept clearly explained, but the visual aid for each step of the STP process was outstanding and clear as well.
Thanks Alex!!
I was let down by my local college by not having teachers to teach networking. I had to do the learning all by myself to get my networking specialisation. Your channel is like treasure to me. Such complex topics explained really beautifully. Thanks guys for making this free!
I'm amazed by how clearly you've explained it. Also you made me chuckle a couple of times. Props for that. Thank you very much for making this video!!
Thanks for the comment Juan. You're welcome
Amazing analysis!! Such a high level networking subject, that too many people mess up, is analysed here in such a way that, even a 10 years old child would do understand. I wish you were my teacher, and I was present in your teaching classrooms. Education needs teachers like you. Thank you!
Thanks for the support Yiannis! Good to hear the video helped!
"Now you may not notice, the switches are arrogant * * * *'s, they all think they should be the root bridge" They bloody well are you legend! Watched this 2 times and it all clicked right into place, also because of this legendary quote i will probably not forget this! Thx so very much!
I came here to comment this
Hi, I've recently bought your course for Ccna, 30% through so far and I adore it. The lab work has definitely helped me define the knowledge of the lessons and keep the skills in ny head through trial and error.
Thank you very much! Really happy to hear you're enjoying the course. More content will be added very soon.
This was by far the greatest STP explanation that I have watched. Great work guys. Keep it up. And quality was superb too.
Thanks Mohammad!!! Appreciate your support bro!
This is an extremely well put together presentation on STP. This will definitely help me to get many of those STP questions on the CCNA exam correct. Thank you for sharing! You rock!
Some of the best explanations i've seen for these topics are on your channel! Keep it up!
Thanks Zeam
I loved your Clear and Precise EXPLANATIONS. Good job. Pls don't stop. Thank you for this.
Brilliant! Best explanation I've seen of STP! Keep up the great work!
Thanks man!!
This is so very clearly explained I just don’t know what to say but WoW Well Explained and Thanks!
This really help connects everything from the book and pieced them together, will try to watch the video a few more times to nail this down, thank you!!!
Thanks Eric. Glad it was helpful! STP can be pretty sticky at first. Keep going and you will nail it.
Well worth subscribing to someone who makes such clear explanations. Unlike some others.
Thanks Brian
You have an amazing talent to teach others these network concepts. I learned so much from you. Thank you BRO!
your explanations are like the computer in the film Matrix that people connect behind their heads.
After watching the video you become an expert in the stuff.
"I know spanning tree"
@@Certbros Top Tier Reply
Very clear step by step explanation, caught by surprise of your sense of humor. Keep it up :)
Haha thanks Nick!
I have never ever seen this kind of clear explanations... this is just perfect and thank you very much
Thanks Paulos!! Glad to hear it!
Thank you so much for this lucid explanation. STP for me previously was a nightmare. Your video is exactly what I needed to get over this scarecrow!
Eugene Che, CCNA student writing from Buea Cameroon, Central Africa.
Thanks Eugene! STP can be confusing!
Love that you put where you're from! Thanks form England!
love you video! the animations makes it so easy to understand. amazing job guys keep it up!
Very well done, helped me understand the topic and it has been a while since I went through this at school. Thank you for making it available.
Thanks Robert! Glad you liked it.
The explanation is just mind blowing, easy to comprehend!!!!
Awesome!!! it is the shortest and clear video explanation of STP that I never seen. Congratulations!!! and tanks.
Thanks Daniel!
This video was very clear and informative. Thank you for taking the time to make and post it. Great work!
Thanks for taking the time to comment!
HOW HAVE I ONLY NOW FOUND YOURE CHANEL????? this is so well explained! Im studying IT and struggle with learning youre so good at explaining thank you!
Thank you for this explanation. It's clear and precise. Thank you.
Thank you for a very clear and understandable lesson on this. Helped me out a lot!
You're welcome! Thank for the comment!
This best and simplest explanation video of STP I have ever seen...thank you so much...
You're welcome Ragesh. Good to hear it helped you out
Amazing, I've been trying to get me head around it for a couple of days now. This was a godsend
Thanks Andrew! It's pretty simple when you break it down.
I’ve watched a lot of videos and on this topic, this explanation is far more in-depth explanation and understanding. And the kind of video I’m looking for that gives understanding. I’ll have to rewatch it, but definitely thanks for these kind of detail understanding videos. People that really want to learn and understand this stuff appreciate these kind of videos.
Thanks Ardent! Glad to hear this helped you out
Brilliant and very clear explanation. Thank you
I prefer hearing to reading things at times because I usually read to relax. Plus I can listen while at work so it constantly refreshes in my head. Thank you guys.
Thanks Anthony! Glad you liked it!
wow!
such a crisp and pretty straight explanations i have ever seen in this topic 👍
Thanks! Appreciate it 👍
I have to agree with the consensus here. Your videos are awesome, informative, and helpful. The best part is it's in clear to understand ENGLISH. Other videos are in broken English and it makes already difficult to understand concepts even more difficult. Thanks for all of your hard work and wish me luck on my exam.
Thanks!! Glad you liked the videos!
Thank you so much for this! You explained it very clearly and in simple terms.
Thanks John
Best STP explanation i have seen so far! Thanks for the great video.
Thanks Marios!
Love the quick math you did there at 12:29
Thanks! It took a few takes to get it right 🤣
@@Certbros haha
damn! this is by far the best and clear explanation of STP I've ever seen. THANKS MAN
Thanks Bashir! Appreciate it 👍
Thank you! Made such a complex topic simple
This is fantastic! Thanks!
Thank you!
Really appreciate the explanation. Thank you for making it easy.
amazing, i learn through diagrams and examples like this. Makes it so much easier to picture in my head. I can't learn from text alone.
Great Video, took me about a day to go through it and fully understand it. Thanks for the animations, they really help.
Thanks. Glad it helped you out!
Your videos are awsome!! you explain really good the information and I can easily learn with them! thanks
Thanks Hermes!
Fixing to have a skills assessment done for a job promotion and this helped a ton! Very informative! Thank you!
Thanks Preston! Did you get the promotion?
Thank you for the detailed information
it was great to see a video with suhc a depth on the topic
This channel is top notch. Thanks for the videos!
This was very informative, Thanks for making this. You guys are awesome !!!!!
Thanks!
the most incredible explanation i ever seen in youtube thank u if you have more videos please let me know.
"You may not notice, but switches are arrogant ***"... Best discription of a switch, ever.
Hahaha!
This video explain it all quite perfectly, and is quite entertaining to watch and learn at the same time, the graphics and animation is clean, and the narrator has a special sense of humor too
Thanks Justin! Really appreciate the comment! Glad you liked it. 👍
Thank You Certbros. You are my type of bros.
Vraiment très bien expliqué merci encore chapeau
Thanks!
Great video, I like how you explained things slowly and clearly. Liked, commented and subscribed.
Thanks bro. Appreciate it!!
Great and clear explanations, Thanks so much!!!
Thanks Jose!
This was incredibly simple explanation. 👍
Helpful information. Thanks so much.
I understood clearly STP after watching this video.
Thumbs up👍👍👍
Thanks for the video very clear and concise
Great vid. Right on point and easy to follow
Thanks Rae!
This is the best vid ever.... Never laughed soo hard listening to a lesson
Love the breakdown, thank you for making this
Thanks David! You're welcome. Glad you liked it.
I am preparing to take Huawei R-S Certification. And a lot of videos explain how to implement in the Switche OS. But none of them explain how it really works like you guys do. Very cool video. Great Job.
10:03
I was not expecting that 😂
😂
This stands out. great work and talent. thank you.
Thanks man!
Love u guys , I'm already waiting for your CCNA course
Thanks Mauricio! I really appreciate your support. 🙏
You can get the course as a pre-launch if you'rere interested, the link is in the description.
Good luck with your studies!
Thanks for making the process simple to understand.
No problem Lisa! Thanks for the comment!
An excellent explanation. I am stuck with this topic and just by playing this once, -all questions are cleared now ! Thanks for the great explanation
Awesome man keep going!
phenomenal content. thank you!
Very helpful to get the mecanism of STP. Thanks
That was a lot but conveyed in a very clear and comprehensive manner. Thank you very much!
Great to hear you liked the video Antonio! Thanks for the comment.
Really god explanied ! Thank you very much.
It will help me for my job :)
Thats actually rly high quality learning course
Good stuff - clearly explained. Keep up the good work! Subscribed
Thanks Alex!
neat and clean video !!
Your vids are very explanatory 👍
Awesome! It can't be clearer than this. Thank you.
Thanks!
I have so much confusion and after watching your animated videos very crispal clear videos
Thank you bro
We need more videos like this
Please don't stop posting it
Thank you
Thank you Kiran! Really glad you liked the videos 👍
best video about STP, pleaze keep uploading the other ccna videos through the animation. God bless you
Thanks Yasir. A lot more videos planned for this year.
thank you you have been such a good help . Im so gratefull
No problem. Thanks!
Really great video man thanks a lot for uploading.
Thanks for the comment!
My new favorite channel !!!
Awesome thanks Scooby!
Subscribed, great explaination!
Nice demonstration and clear presentation.
Thanks Joel!
This is legendary. Blesss
Very informative video!
Great video, well explained, well animated.
Thanks!
Extremely helpful - thank you! :)
In particular I appreciate the way you explain the concepts in very simplistic terms first, followed by then explaining an issue that happen... how the issue would happen... and then how that issue is addressed.
Then you move on to explain how yet a different issue could happen - and again explain what would happen, etc.
By doing it this way it allows viewers to understand the concepts, but also recognize if they are having the issues you explain as potential issues.
Thanks again! :)
PS. perhaps I missed it... but do you have any videos on VLT Fault Domains?
Hi there, we just covered this Video in our German IT class. Thanks for uploading this!
That's awesome!!! Tell your class I say hi!
Very useful, as was the OSPF video. Found the Cisco online material a bit confusing. I'm glad I found this channel
Great to hear! Glad to have you.