From: Edison Ortiz (edisonmortiz@gmail.com)
Date: Tue Feb 20 2007 - 15:43:33 ART
The formula is Bridge Priority + sys-id-ext
sys-id-ext usually correlates to the VLAN number
In situations where you have a trunk port, the interface will be listed for
each VLAN that is participating on the trunk port
and each VLAN will have a different Bridge Priority ID for the switch.
sh spanning-tree | inc Bridge ID
Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)
Bridge ID Priority 24580 (priority 24576 sys-id-ext 4)
Bridge ID Priority 24581 (priority 24576 sys-id-ext 5)
Bridge ID Priority 24582 (priority 24576 sys-id-ext 6)
Bridge ID Priority 24583 (priority 24576 sys-id-ext 7)
Bridge ID Priority 24584 (priority 24576 sys-id-ext 8)
Bridge ID Priority 24585 (priority 24576 sys-id-ext 9)
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
----- Original Message -----
From: "Gobind" <gobind@inbox.com>
To: <ccielab@groupstudy.com>
Cc: <bdennis@internetworkexpert.com>
Sent: Tuesday, February 20, 2007 1:27 PM
Subject: Bridge Priority
> Hi Guys,
>
> I have some confusion wiht the Bridge Priority.In Some CBTs I am getting
> to hear that:-
>
> Bridge Priority is Default Priority(32768) - Vlan Number
>
> I asked my friend,he said Default Priority is Default Priority + Vlan
> Number
>
> In one Cisco Dumentation it is written:-
>
> "Each VLAN on each network device has a unique 64-bit bridge ID
> consisting of a bridge priority value, an extended system ID, and an STP
> MAC address allocation"
>
> Source:- http://www.cisco.com/en/U
> S/products/hw/switches/ps708/products_configuration_guide_chapter09186a008016
> 0a5b.html#wp1040218
>
> I am really confused(maybe I am getting it wrong) what Priority(in STP
> is),also I am not getting if the Priority is Default priority + Vlan
> Number or - Vlan Number then what Vlan Number is it refering to? I mean
> the Trunk belongs to every Vlan then which Vlan Number it takes while
> making the election.(when it sends BPDU i.e.)
>
> Gobind
>
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