Confused about STP designated ports

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Trying to go through some exercises, and I'm really confused.

Imagine 4 switches arranged in a square.  They are connected around
the perimeter, but also in an "X" through the center.

SW A  ----------SW B
  |  \\                 / |
  |   \\               /  |
  |    \\             /   |
  |     \\           /    |
  |      \\         /     |
  |        \\     /       |
  |           X         |
  |        /      \\      |


SW C                 SW D

(I don't want to do any more...you get the idea).

All switches have the same priority, and links are a mixture of
100Mbps and 1 Gbps.

I set this same topology up in Packet Tracer, and arranged the
switches so that tha MAC addresses have the same relationships as they
do in the exercise.  I wanted to see how PT assigns things so I could
check my own work.

PT says SW A is the root bridge, SW B has one root, one DP, and one
blocked port.  SW D has one root and 2 DPs.  SW C has one root and 2
blocked ports.

Is there only one solution, or does it depend on the order that you do
things?  If I start with SW B and start calculating path costs and
assigning port designations, I get the same answer as PT.  But if I
start with, say, SW C I get something different.

BTW...this is page 196 of the LAN Switching and Wireless Study Guide.

Re: Confused about STP designated ports
I decided to make a screen cap, in case someone offers to help.

http://i80.photobucket.com/albums/j196/mitchb2/Capture.jpg

Re: Confused about STP designated ports

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According to your picture, Switch B should be the root because
as you said all the switches have the same priority, and Switch B has
the highest MAC address.

Not familiar with the document you are reading, but based on your pic -
I think things are wrong ..............









Re: Confused about STP designated ports

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Lowest  MAC gets elected.

From the Official Cert Guide:
"If a tie occurs based on the priority...the switch with the lowest
MAC address portion of the bridge is the root."

Re: Confused about STP designated ports

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You are correct.
Lesson learned - never attempt to answer tech posts
when you're on valium and vicodin after surgery.....
That's a big D'uh on my part !
;-)



Re: Confused about STP designated ports
On Fri, 13 Feb 2009 20:58:32 -0600, "John Agosta"

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Hey, I've been there!
Kudos that you're studying anyway.

Hope you're okay and everything went well.

Re: Confused about STP designated ports
Mitch@_._ wrote:
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Only post responses after significant amounts of zinfandel.

Re: Confused about STP designated ports

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Don't really care for wine.....



Re: Confused about STP designated ports

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Well, I'm not really "studying," just had a brain tart.....



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