CBT nuggets, ccnp switch, STP

aocferreiraaocferreira Posts: 50Member ■■□□□□□□□□
Hello,

i think there's a mistake on stp videos for CBT nuggets series. According to attached pic, can you please confirm?



From switch E point of view, shouldn't Root Port be the one towards switch C ?
And from switch F point of view, shouldn't root port be the one towards switch C?

Later on the video, he says that root port of E goes towards D and root port of F goes towards D also.

Please confirm.

Thanks in advance.

Comments

  • tomtom1tomtom1 Posts: 375Member
    I think you're correct. The process of electing the root port should be like this.

    1) Lowest port cost
    2) If equal port cost, lowest BID of the switch
    3) If equal port cost and BID, the lowest port number is used

    So when we run that logic against the given topology, switch C should be preferred over switch D unless we're both missing something :)
  • Vask3nVask3n Posts: 517Member
    I made a quick and dirty edit to show the root ports should be, let me know if there are any errors on the diagram.

    Working on MS-ISA at Western Governor's University
  • aocferreiraaocferreira Posts: 50Member ■■□□□□□□□□
    Vask3n, that was also my conclusion.

    tomtom1, thanks for feedback also.

    So, it seems that they got this wrong...
  • theodoxatheodoxa Posts: 1,340Member
    Root Path Cost is the same going E-D-A or E-C-A. The other paths would all have a higher Root Path Cost. So, the root port would face either D or C. Lowest Sender BID should win. All the switches seem to have default priority, so lowest MAC Address determines who has the lowest Sender BID. I can't read the full MAC Address for Switch D, but if it follows the apparent pattern, C should have the lowest Sender BID.

    Lowest Root Path Cost
    Lowest Sender Bridge ID
    Lowest Sender Port ID
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  • Danielh22185Danielh22185 Posts: 1,195Member
    theodoxa wrote: »
    Root Path Cost is the same going E-D-A or E-C-A. The other paths would all have a higher Root Path Cost. So, the root port would face either D or C. Lowest Sender BID should win. All the switches seem to have default priority, so lowest MAC Address determines who has the lowest Sender BID. I can't read the full MAC Address for Switch D, but if it follows the apparent pattern, C should have the lowest Sender BID.

    Lowest Root Path Cost
    Lowest Sender Bridge ID
    Lowest Sender Port ID

    ^^ This guy nailed it. Yet also brings up a good point. You cannot see the entire MAC address listing for Switch D. However it does seem to follow a pattern and I would assume it should be 32768.0000.0000.000d. Which would make the ports facing switch C the root port as others have already confirmed.


    Lowest Root Path Cost
    Lowest Sender Bridge ID (MAC address in this case the priority values match on all the switches)
    Lowest Sender Port ID

    On that note I am going to re-watch this nugget just to confirm for fun and would be good practice for me.
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  • JeanMJeanM Posts: 1,117Member
    Pretty surprising when these errors are discovered in the training material that gets released isn't it ? icon_sad.gif
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  • Danielh22185Danielh22185 Posts: 1,195Member
    JeanM wrote: »
    Pretty surprising when these errors are discovered in the training material that gets released isn't it ? icon_sad.gif

    Happens all the time!
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