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Gold

STP port priority and cost

What diffence in spanning tree between port cost and priority. I understand cost - default value is derived from the media speed of the interface. But for what is used port priority???

THX

3 REPLIES
Silver

Re: STP port priority and cost

STP decisions are based on the following in descending order:

1. Bridge ID - this is priority + MAC

2. Root Cost - added inwards

3. Sender bridge ID -

4. Port ID - the first 6 bits of which are priority.

For all of the above, lower values are better. Root Cost is second in the decision, port ID is last.

Thanks.

Re: STP port priority and cost

hi,,,

priority is used for the election of root port...lowest the priority and mac address value switch will become root bridge... and root bridge is the most important part of switching networks...so u can say the priority is the most important parameter...

rate this post if it helps

regards

Devang

Re: STP port priority and cost

Hi,

The Port Priority Parameter (in local switch) is used to influence the Switches that connect to the local switch and is influenced by the local switch for Spanning tree Convergence. The Port Priority Parameter will be carried in Spanning Tree BPDU for influencing the dependant switches in making Root Port Decisions.

The Port Cost Parameter is used to influence the port that would be designated as root port. The Port Cost parameter acts as a local parameter in deciding the Root Port in the Switch

Regards,

Sridhar.

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