port Priority

mcse_696

if you have 2 switch they are connected with to links i want to change the priority of the port that is block on which switch i have to change the priority i tried to change on the switch its have the block port nothing changed please help

EdTheLad

Change the spanning-tree port cost on the upstream switch.The port prioity would only be needed if the two ports on the local switch were connected to the upstream switch via a hub.Port cost is sent in the bpdu, so you need to lower the cost on the upstream switch to make the current port forwarding.

mcse_696

ok as i read if you want to change the cost of the link to become root port you have work on 2 switchs they are connecting directly ,however if i dont want play with path cost i have the other choise port priority on which switch i must change the port priority just confusing to understand
lowest sender port priority could you explain with simple way please i m just studing and i stuck on lowest sender port priority where should I do the configuration of port priority

APA

There is a specific order called 'spanning-tree tiebreakers' which are used to make decisions on port status....... These are contained within BPDU's

During this time the two switches compare the following in order until one starts sending a superior BPDU

1) Lowest Root Bridge ID
2) Lowest Root Path Cost Path to Root Bridge
3) Lowest Sender Bridge ID
4) Lowest Sender Port ID(Priority)

Quite possible nothing is occuring because the upstream switch is still sending superior BPDU's due to the first three tie-breakers......

Double check your spanning-tree config on both switches..... The switch which currently has a blocking port must start sending superior BPDU's for the port to move to forwarding state...

Hope this helps

EdTheLad

A.P.A wrote:

There is a specific order called 'spanning-tree tiebreakers' which are used to make decisions on port status.......

1) Root Bridge Priority
2) Lowest Cost Path to Root
3) Sender Bridge ID
4) Sender Bridge Port ID(Priority)

Quite possible nothing is occuring because the upstream switch is still sending superior BPDU's due to the first three tie-breakers......

Double check your spanning-tree config on both switches..... The switch which currently has a blocking port must start sending superiot BPDU's for the port to move to forwarding state...

Hope this helps

Yep, got a bit muddled, the priority is sent by the upstream switch, the cost is local.Ram update successful.

APA

yeah Ed that's right... the path cost is local to the switch but it adds this to the 'Root Path Cost Value' which is within the BPDU....

Each switch adds it's path cost value to the root path cost value in the BPDU which makes it a cumulative value as it passes from switch to switch....

APA

by the way MCSE.... i just re-read your second post...

port priority in fixed port density switches is always 128.(port number)

eg.. Fa 0/24 = Port Priority 128.24

but you can modifiy this... it is done on a per interface basis

interface fa 0/24
spanning-tree port-priority (value)

hope this helps