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Re: Bridge Priority posted 02/20/2007
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I am not sure if you refering to a specific lab exercise, but in real environments you can select which switch you want to be the Root Bridge for specific vlans by lowering the priority from the default 32768. The lower the priority the more prefered to be the root (example 32000). If you want to FORCE a specific switch to be the root then you set priority 0. For example:

spanning-tree vlan 10-14 priority 0 (This will set this switch to be the root for vlans 10,11,12,13,14)

You can set a different root bridge for each group of vlans for load balancing. You can direct certain vlans traffic through one distribution switch and other vlans through the other distribution reduntant switch for load balancing L2 traffic.

Usually is good to set the L3 distribution switches as the Root bridges for the vlans attached to the access layer switches attached to it.

Thanks,

Loizos Y.
CCIE#10702 R & S 



Gobind <gobind@xxxxxxxxx> wrote: 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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