From: anthony.sequeira@thomson.com
Date: Tue Feb 20 2007 - 22:15:41 ART
And forgive me if it was already mentioned in the thread....but WHY do
this?
So you can use ONE MAC address to create a unique Bridge ID for a whole
bunch of VLANs.
Anthony J. Sequeira
#15626
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Tuesday, February 20, 2007 7:40 PM
To: 'Lou Ioanni'; 'Gobind'; ccielab@groupstudy.com
Subject: RE: Bridge Priority
I think you'd have to sit there with a lot of math to verify that, but
it's
not accurate anyway, so save yourself some time. :)
The old way for Bridge ID was 16-bit priority + MAC address = 64 bits.
Now, the bridge ID is still 64 bits, but instead of having 16 bits for
priority (who has 65000 switches anyway?), there are 4 bits used for
priority and then 12 bits used for VLAN ID. So that's why you can get
some
strange values.
So the priority field is still 16 bits:
ppppvvvvvvvvvvvv
Where p = priority and v = vlan ID.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Lou
Ioanni
Sent: Tuesday, February 20, 2007 5:28 PM
To: Gobind; ccielab@groupstudy.com
Subject: Re: Bridge Priority
Right. You do not deduct vlan number from default to get priority. What
confused you is the way they map vlans to priorities ex. 2-32768,
3-4094,
etc
I never heard of such formula. I will be very surprised if there is
any.
Loizos Y.
CCIE#10702 R & S
Gobind <gobind@inbox.com> wrote:
So in no case this is true,right?:-
Bridge priority = Default bridge priority - Vlan Number
I heard it in CBT was got confused!
> -----Original Message-----
> From: louisccie_r_s@yahoo.com
> Sent: Tue, 20 Feb 2007 11:21:11 -0800 (PST)
> To: gobind@inbox.com, ccielab@groupstudy.com
> Subject: Re: Bridge Priority
>
> Yes each vlan has its own root depending on the priority. If
> priorities are the same then it uses the mac to select the root. Each
> vlan and priorities are combined to create a unique ID. Check the
> floowing link for a siminlar question and answers:
>
> http://www.velocityreviews.com/forums/t37177-bridge-priority-and-sysid
> ext-number.html
>
> Gobind wrote: If the sys-id-ext usually correlates to Vlan Number,it
> means like for Vlan Number 1 the sys-id-ext would be 1,right? it is
> taken automatically or manually? I am confused about the part that the
> If in a switch every Vlan has its own priority then when the Root
> Election occurs,does it occurs to every Vlan,lets say there are
> 3 Vlans and what if it have different Priority then is it also
> possible that on Switch would be Root Bridge for 1 Vlan and not other
> two(due to higher Priority)?
>
>
> -----Original Message-----
> From: louisccie_r_s@yahoo.com
> Sent: Tue, 20 Feb 2007 10:59:29 -0800 (PST)
> To: gobind@inbox.com, ccielab@groupstudy.com
> Subject: Re: Bridge Priority
>
>
> 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 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_chapter09186
> a008016
> 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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This archive was generated by hypermail 2.1.4 : Thu Mar 01 2007 - 07:38:47 ART