From: Daniel Valle (danielfrvalle@gmail.com)
Date: Thu Aug 21 2008 - 16:06:23 ART
Just to complete the explanation:
Sw2 receives bpdus via 3 trunks. It compares the Bridge ID, as it's the
same, it'll check for the path cost, the path cots, as I said, Is
manipulated via the port-cost command in the root or alternate port. if it
is still the same, then it'll check the port-id sent by SW1. The port-id is
the port-priority+ port-number. the port chosen will be the one with the
lowest port-id, i.e, if the port-priority is the same, than the interface
number will be the tie-breaker.
This is why we usually configure port-priority in one switch and the
port-cost in the other one.
I think that's it.
Daniel.
On 8/21/08, Daniel Valle <danielfrvalle@gmail.com> wrote:
>
> Mark,
>
> Cost we use in the incoming switch, for example.. if SW1 is the root, the
> Cost must be applied in SW2, otherwise it'll not any effect ( this is
> similar to IGP metrics. the metric that matters is always the inbound
> interface)
>
> port priority is to be configured in the designated port. i.e, in your
> case, you should configure port priority in SW1 ( which is the root)
>
> if you have a 3rd switch SW1==SW2==SW3, you must use port-priority in the
> SW2 port to influence SW3 decision.
>
> resuming: use Port-priority in designated ports and use port-cost in root
> or alternative(blocked) ports
>
>
> HTH,
>
> Daniel
>
>
>
> On 8/21/08, Mark Stephanus Chandra <mark.chandra@gmail.com> wrote:
>>
>> Dear All Expert,
>>
>> I'm kinda confuse with the used of SPT port-priority and SPT path cost.
>>
>> Actually when I do my IEWB vol 2 lab 11.
>>
>> To influence path decision, when doing SPT.
>>
>> SW1 --------------- SW2
>>
>> SW1 is the root bridge
>>
>> Actually SW 1 have three trunk connection to SW2, let say FA0/15,fa0/14
>> and
>> fa0/13
>>
>> so the command is, SW1 should use Fa0/15 as its primary link to SW2, when
>> fa0/15 fail, then it choose fa0/13 and the last is fa0/14.
>>
>> So, if I configure fa0/15 with spt cost 1 , do i have the same result if i
>> configure fa0/15 with spt port-priority of let say 15 (the default is 128
>> right ?)
>>
>> So kinda confuse when do we have to use spt priority or cost
>>
>> Thanks in advance
>>
>>
>>
>>
>> --
>> Mark Stephanus Chandra
>>
>>
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>>
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