Hi Rene,
very interest read and clear understanding…may appreciate update MSTP,RSTP,PVSTP…
Fantastic explanation …
Please correct the port number with Fa0/14
Fa0/24 is a designated port and in (FWD) forwarding mode.
• Fa0/17 is a root port and in (FWD) forwarding mode.
Thanks Jagan! I also wrote this post on MST:
I agree 
its ultimate… very informative in easy way.i am very thank full to you Rene for making concecpt so straight and easy…
Thanks & fixed 
thnx . it was very helpful
Great, great, great … Thanks. So I am preparing the CCNA certification but I’ve spent lot of time on reading the 640-802 version rather than the 200-120, what would be your advices ? Thanks in advance.
It’s best to switch to the 200-120 material, there have been quite some changes to CCNA.
Rene
Very clear and helpful description. I especially appreciate the clarity and clean look of the visuals.
Is this info that is also available in your “Mastering CCNA” book?
Rene,
What happens when link between Switch C to Switch A goes down.
how the port types vary in this case?
Which will become non designated port?
Regards,
Veerender
Hi Veerender,
With the link between Switch A and Switch C gone, it will look like this:
SwitchA is the root bridge so it’s interfaces are always designated.
Interface Fa0/14 on Switch B will be the root port, and Fa0/16 on Switch C will also become a root port.
Interface Fa0/16 on Switch B will be a designated port.
There won’t be a non-designated port in this example, there’s also no loop in the topology.
Rene
Rene,
That was very helpful.
Veerender
Dear Rene,
The pictures are not appearing , please fix it.
Thank you , and appreciated.
Hey Rene,
In regard to the STP timers you say -
“Forward Delay: It takes 15 seconds to move to the forwarding state”
Forward Delay is the amount both the Listening and Learning states last. By default, each state lasts 15 seconds.That’s a total of 30 seconds to move to the forwarding state not 15.
Hi Alfredo,
You are right, I just rewrote this sentence so it makes more sense.
Rene
Dear Rene,
Thank you for this post. I would like to ask you one question and confirm about another one.
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You wrote that we can change priority of a switch. If we do not change it based on which principle it is assigned automatically to the switches?
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On your first example one of the ports of switch C is in blocking mode. Let’s suppose that there is some data to send from switch B to switch C. Switch B will forward the data directly to switch C, right? If there is some data to send from switch C to switch B then switch C will forward the data through switch A, right?
Thank you for your time.
Best regards,
Aisha
Dear Aisha,
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Spanning-tree uses the Bridge ID to determine who will be the root bridge. The Bridge ID consists of the priority + MAC address. If you don’t touch the priority then the MAC address will be the tie-breaker.
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Switch B and C will both send frames towards Switch A. Switch B will learn the source MAC addresses from hosts behind Switch C on its uplink to Switch A since Switch C doesn’t forward anything out its blocked interface.
Rene
Hallo René,
So we have to block a link (port on the Switch C toward Switch B) for avoiding a loop ?
But it is not efficient for the bandwidth utilization (we have to go through Switch A to reach Switch C), how can we improve that ?
Thks in advance
Hi Prince,
That’s right, this is an “issue” with spanning-tree, it just blocks the link so it won’t be used. There are two methods to work around this:
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Use PVST where we have a different topology for each VLAN: https://networklessons.com/cisco/per-vlan-spanning-tree-pvst/
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Don’t use the same VLAN on more than one switch, this means we need a design with routers. Instead of “switching” traffic we “route” it. The advantage is that routing protocols can do load balancing on multiple links.
Rene