From: Marut S@MS@DCTH-BKK (S@MS@DCTH-BKK)
Date: Sun Mar 25 2007 - 08:32:42 ART
Hi Group,
I have found something interesting about this topic.
Previously I understand that spantree mst xx root primary will make
switch to be root no matter what priority value of the other switches in
the domain. But from my testing result. I found that if other switch was
setup as priority 0. spanning-tree mst xx root primary is useless.
I have switches 1 & 3. Both run MST.
------------------------------------------------------------------------
-------------------------------------------------------
SW1#sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 0016.c859.7980 priority 32779 (32768 sysid
11) -------> SW1
Root address 000c.8555.7880 priority 32779 (32768 sysid
11) --------> SW3
SW1#sh run | i span
spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst configuration
SW3(config)#do sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 000c.8555.7880 priority 32779 (32768 sysid
11)
Root this switch for MST11
------------------------------------------------------------------------
-------------------------------------------------------
I want sw1 to be root switch
SW1(config)#span mst 11 root prim
SW1(config)#do sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 0016.c859.7980 priority 24587 (24576 sysid
11)
Root this switch for MST11
SW3(config)#do sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 000c.8555.7880 priority 32779 (32768 sysid
11)
Root address 0016.c859.7980 priority 24587 (24576 sysid
11)
------------------------------------------------------------------------
----------------------------------------------------------
Then I want to test if I setup priority for mst 11 at sw3 to be 0. Will
sw1 still adjust itself to be root ?
ANSWER IS NO
SW3(config)#span mst 11 pri 0
SW3(config)#do sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 000c.8555.7880 priority 11 (0 sysid 11)
Root this switch for MST11
SW1(config)#do sh span mst 11
##### MST11 vlans mapped: 11
Bridge address 0016.c859.7980 priority 24587 (24576 sysid
11)
Root address 000c.8555.7880 priority 11 (0 sysid 11)
SWITCH 1 NOT ADJUST ITSELF TO BE ROOT.
------------------------------------------------------------------------
-------------------------------------------------------------
THE CONCLUSION IS : if you asked to setup the switch to have best chance
to be the root switch. Don't use spanning-tree mst xx root primary. But
use spanning-tree mst xx priority 0 instead. (Try setup priority 0 at
sw1 first. Sw3 won't allow me to configure root primary command.). Seem
like spanning-tree mst xx root primary will adjust to the lowest value
at 4096 and no more ( Adjust only one time you enter this command. In
the show run you will see it as spanning-tree mst xx priority 4096..
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/cr/
cli3.htm#wp1946716
Anyway if both switch is setup as priority 0. tie-break is
mac-address. How could I forced mac-address of bridge-id ?
Best Regards,
Maruto
-----Original Message-----
From: William Walla [mailto:wwalla@gmail.com]
Sent: Sunday, 25 March, 2007 2:26 AM
To: Marut S@MS@DCTH-BKK
Subject: Re: Ask for help : Best chance to set the switch to be root
spantree vlan XX priority root
William Walla
713-252-6203
-----Original Message-----
From: "Marut S@MS@DCTH-BKK" <Marut.s@datacraft-asia.com>
Date: Saturday, Mar 24, 2007 2:08 pm
Subject: Ask for help : Best chance to set the switch to be root
Hi group,
I have a question about best chance for set up the switch to
be
the root switch. Spanning-tree vlan xx priority 0 command that should be
used.
But if other switch has been setup priority = 0 too. Tie
break
is mac-address.
Question is how could I setup mac-address for bridge-id ?
Regards,
Maruto
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