From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Tue Apr 04 2006 - 02:54:43 GMT-3
Hi Wayne ,
Some additional notes !!! From the point of view of Exam !!!
Pls. see my reply inline
Thanks and Regards
Arun
-----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
CCIE
> KH49279
> Sent: Tuesday, April 04, 2006 5:58 AM
> To: ccielab@groupstudy.com
> Subject: STP and Preferences
>
> Group,
>
> I just want to make sure I am understanding something. I am sure I do, but
> the warm fuzzy is necessary right now.
>
> For STP on a 3550.
>
>
> Root Bridge
>
> If I have a two trunk links between sw1 and sw2 and I want a particular
> bridge (in this case sw1) to be root
> 1) I could use the 'spanning-tree vlan x,y,z root primary command to make
> the bridge root bridge for the vlans x,y,z.
> 2)I can also use the 'spanning-tree vlan x,y,z priority n' global command
to
> assign a value to influence the natural election process for the root
> bridge.
>
[arun]
Use the first one if you are not sure of what is the priority configured on
the other switches and you are not bothered to find priority of other
switches .
Use the second one if you clearly know the priority configured on all the
other switches or will to find out their priorities .
Note : From the exam point of view both are same and valid , unless and
untill you specifically asked not use the priority command !!!
[arun]
> Port Preference
>
> I will assume that I have three ways to make a particular port prefered
over
> another.
> 1) interface command spanning-tree port-priority n to influence the
natural
> selection
> 2) interface command spanning-tree cost n to influence the natural
selection
> 3) allow the tie-breaker to occur being lowest mac address for the
> interface.
>
[arun]
If you want make a port blocking or root port you can follow the above
techniques . In doing so we can keep the following rules in mind ...
1) If you are changing the port priority change it on Root Bridge . If you
do it on non-root bridge you will not achive any thing from it .
Note : Default port priority is 128. Lower prioriy will be preferred .
2) If you are changing port cost that do it on non-root bridge .If you do it
on root bridge you will not achive any thing from it .
Note : Default depends on Bandwidth ( For fast ethernet it is 19 )... Lower
cost will be prefered .
3) I am not sure Mac address could influence the blocking port-rootport
selection .
4) If the question says do not modify priority or cost ...than think of
changing the Bandwidth ( using the command "bandwidth <bw> " ) on the
non-root bridge . This will have in-direct effect on cost thus can control
the root-port & blocking port selection .
[arun]
>
> TIA,
>
> Wayne
>
>
> Dream as if you'll live forever. Live as if you'll die today. - James Dean
>
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