Spanning -Tree D calculation I have a pkt file attached on this post also my topology(based on my own calculations). both on the zip file. Calculating an d Spanning-Tree Topology. By Keith Bogart. [email protected] Cisco. TS Training Team. As an instructor, I enjoy teaching students how the d. The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology STP was originally standardized as IEEE D but the functionality of spanning tree (D), rapid spanning tree (w), and multiple spanning On this root bridge the preferred and non-preferred links are calculated.
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Spanning-tree is a protocol that runs on our switches that helps us to solve loops. In the picture above we have two switches. These switches are connected to each other with a single cable so there is a single point of failure.
To get rid of this single point of failure we will add another cable:. With the extra cable we now have redundancy. Unfortunately for us redundancy also brings loops.
Why do we have a loop in the scenario above? Let me describe it to you:. Do you see where this is going?
We have a loop! Both switches will keep forwarding over and over again until the following happens:. Besides ARP requests there are many frames that are broadcasted. Spanning-tree will help us to create a loop-free topology by blocking certain interfaces. Topoloby have three switches and as you can see we have added redundancy by connecting the switches in a triangle, this also means we have a loop here.
EOS Section 24.2: Spanning Tree Overview
I have added the MAC addresses but simplified them for this example:. In this BPDU there are two pieces of information that spanning-tree requires:.
The BPDU is sent between switches as shown in the following picture:. So who will become the root bridge? Since the priority is the same on all switches it will be the MAC address that is the tiebreaker.
The ports on our root bridge are always designated which means they are in a forwarding state. Take a look at the following picture:. Take a look at my example:. Each interface has a certain cost and the path with the lowest cost will be used. So which port are we going to shut down? You may cancel your monthly membership at any time.
The cost is 19 because the line speed connecting the switches is fast ethernet megwhich is assigned a cost value of 19 by STP. In other words, BPDUs must continue to be received in order f. Ask a question or join the discussion by visiting our Community Forum.
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Introduction to Spanning-Tree |
Explained As Simple As Possible. Full Access to our Lessons. More Lessons Added Every Week! Alan, The cost is 19 because the line speed connecting the switches is fast ethernet megwhich is assigned a cost value of 19 by STP.
In other words, BPDUs must continue to be received in order f Continue reading in our forum. Atlast my assumption is correct. Thanks for your lab work and confirmation. Send this to a friend Your email Recipient email Send Cancel.