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TOPIC: Spanning Tree Protocol

Spanning Tree Protocol 10 years 1 month ago #16173

  • zenzippy
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Hi all, first post :)

Really trying very hard to understand this at the moment. This is pretty hard to explain without a diagram...

Say if I had 6 switches,

3 of the switches were joined together one on top of the other from segment 1 to segment 2 with 100Mb fastEthernet links
Now the other 3 switches were arranged in the same fashion, though this time they had 10Mb ethernet links.

So basicaly we have redundancy with two paths between both segments.. The root bridge will be the one in the middle of the first three switches.
How many ports on the designated switch will be designated ports, I thought 2 because thats the only path to the root bridge with the lowest cost...

Is that correct? because it doesn't say anything about how many ports on designated switches are allowed.

TIA
zenzippy
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Re: Spanning Tree Protocol 10 years 1 month ago #16177

  • zenzippy
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I suppose it would be a root port, not a designated port on the second port towards the root bridge...
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Re: Spanning Tree Protocol 10 years 1 month ago #16307

  • Dove
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Its Root Ports not a Designated Ports.

Ports in Desgnated switch which is having the least cost to reach the Root Bridge is call the Root ports. As well as the ports which is used to pass the data from one segment to another segment is call the Designated port.

so as per your setup two Root Ports are thr.


Regards
Dove

Dove
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Re: Spanning Tree Protocol 10 years 1 month ago #16356

  • zenzippy
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Ok

It says in the cisco book the spanning tree protocol must select one root port on non root bridges.

So its possible to have two root ports on one switch?

Thanks.
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Re: Spanning Tree Protocol 10 years 1 month ago #16366

  • jwj
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It's possible with Per VLAN Spanning Tree or Multiple Spanning Trees. PVST is the normal spanning tree that newer Cisco switches run.
-Jeremy-
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Re: Spanning Tree Protocol 10 years 1 month ago #16372

  • Dove
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No, its not possible. If a switch having two ports connecting to root switch then it will block one port which is having the highest cost based on its selection algorithm.

So a switch can have one root port and another one will be blocked.


Hope it will clear you.


Regards,
Dove.

Dove
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