Networking & Wireless forum

General discussion

Need feedback on a doc I wrote - STP-Root Port Election.

by Gerald C. Paciello / January 30, 2016 3:55 PM PST

I am currently studying for CCNA R&S 200-120 exam. and as I cover each topic, I like to write something about it. Your feedback is beneficial two fold; I check that my understanding is correct and I learn more from you guys.

Many thanks in advance.

Root Port Election Process.

The RB floods its CBPDU advertising a Cost to RB value of 0, because it is the RB so there is no cost to get to the RB, of course. The other switches will receive this CBPDU and add the cost of the port it received the CBPDU on, to the advertised Cost to RB value on the CBPDU received, which is 0.

For example, if the CBPDU comes in Fa0/1, the switch will ad 19 to 0 (if you look at the Port Costs table you can see that the cost for a 100Mbps link is 19) so, 19 + 0=19. So this switch will forward a copy of the CBPDU received advertising a Cost to RB value of 19. The next switch will receive this BPDU and again add the cost value of the port it received it in (let´s say that it is a 1Gbps link) to the Cost to RB value advertised in the BPDU received, which is 19, so 4 + 19=23. When this switch send its own BPDU, it will advertise a Cost to RB value of 23. This same process will repeat until the port with the lowest -cumulative- path-cost on each non-RB switch is elected Root Port.

Let´s follow this same example step by step:

1.RB floods a CBPDU advertising a Cost to RB of 0 (zero). This makes sense because there is a cost of 0 for the RB to get to the RB.

2.Non-RBs receive this CBPDU and they add the cost of its port to the advertised Cost to RB in the CBPDU. So Cost to RB-0 +100Mbps cost-19 = 19.

3.The non-RB sends a copy of the CBPDU advertising a Cost to RB of 19 (This is true for this non-RB on this step of our example. The other non-RBs in the topology might advertise a different Cost to RB value depending on the cost value of the port they received the CBPDU on.)

4.The next non-RB downstream receives the BPDU advertising a Cost to RB of 19. The port in which this BPDU came into is a 1Gbps port, which has a cost of 4. The switch adds 19 + 4 = 23 and sends out a BPDU with an advertised Cost to RB of 23.

5.The process repeats until all the RPs have been elected.

Discussion is locked
You are posting a reply to: Need feedback on a doc I wrote - STP-Root Port Election.
The posting of advertisements, profanity, or personal attacks is prohibited. Please refer to our CNET Forums policies for details. All submitted content is subject to our Terms of Use.
Track this discussion and email me when there are updates

If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.

You are reporting the following post: Need feedback on a doc I wrote - STP-Root Port Election.
This post has been flagged and will be reviewed by our staff. Thank you for helping us maintain CNET's great community.
Sorry, there was a problem flagging this post. Please try again now or at a later time.
If you believe this post is offensive or violates the CNET Forums' Usage policies, you can report it below (this will not automatically remove the post). Once reported, our moderators will be notified and the post will be reviewed.
Collapse -
Just FYI
by R. Proffitt Forum moderator / January 30, 2016 4:19 PM PST
Collapse -
Yes, you are right.
by Gerald C. Paciello / January 30, 2016 4:48 PM PST
In reply to: Just FYI

It´s me... same person... That is why the texts are identical....

So let me get this straight; you thought, for some odd reason, that I just copied something from somewhere, pasted it here and called my own. Claiming that I am taking the cert. exam....
Why, why would anyone do that... well... may be I am being too innocent here... but come on!!!

Anyway R.Proffitt (nice name dude), if you have the knowledge to judge my understanding on Root Port Election... please do so...

Thanks again....

Collapse -
Oh, I think Bob has the nous.
by Dafydd Forum moderator / January 30, 2016 4:54 PM PST
In reply to: Yes, you are right.

Dafydd.

Collapse -
It's also a rehash of something I read long ago.
by R. Proffitt Forum moderator / January 30, 2016 4:57 PM PST
In reply to: Yes, you are right.

I know it's now hard to re-hash content like this but a fast re-read of some Cisco PDF sounds like yours is OK. I didn't claim it was a copy but how to write about port election without duplicating prior works is, you can't avoid it.

Collapse -
Right again...
by Gerald C. Paciello / January 30, 2016 5:08 PM PST

You could compare the technical writing. I mean I am NOT a technical writer, heck!.. I am not a writer of any kind. But if you don´t see much difference (not in what it says but how it is said)... well, kudos for me then. Thanks for the complement!

Thanks again man!

Collapse -
Also...
by Gerald C. Paciello / January 30, 2016 5:10 PM PST

I do have other docs on learningnetwork.com, search for Spanning Tree Protocol - CCNA by GCP.pdf if interested.

Collapse -
so it's plagearism?
by Dafydd Forum moderator / January 30, 2016 5:16 PM PST
In reply to: Also...

Dafydd.

Collapse -
Locking.
by R. Proffitt Forum moderator / January 31, 2016 7:31 AM PST

It appears you are promoting your content but do try to complete your works and turn them into an E-book. That way you can put it up on say the Kindle.

Locked.

Popular Forums
icon
Computer Newbies 10,686 discussions
icon
Computer Help 54,365 discussions
icon
Laptops 21,181 discussions
icon
Networking & Wireless 16,313 discussions
icon
Phones 17,137 discussions
icon
Security 31,287 discussions
icon
TVs & Home Theaters 22,101 discussions
icon
Windows 7 8,164 discussions
icon
Windows 10 2,657 discussions

FALL TV PREMIERES

Your favorite shows are back!

Don’t miss your dramas, sitcoms and reality shows. Find out when and where they’re airing!