From: Joseph Brunner (joe@affirmedsystems.com)
Date: Wed Oct 03 2007 - 21:23:45 ART
Yikes! I'm a NCO and Brian's a 4-star general, but anyway.
As a student of Brian's VOL II. Workbook dojo I learned we change stp PORT
PRI to influence root path selection going downstream (root to leaf), while
we influence COST to influence root path selection going upstream (leaf to
root). Just remember COST is added OUT of a port as the BPDU leaves the
bridge its added.
As far as setting root bridge.
Read the task. it may say something like "Sw2 should be the root for odd
vlans, while sw3 is the root for even vlans. Each switch will become
secondary for the other root bridge's vlans (I.E. Sw3 will be root for odd
vlans if switch 2 is unavailable)".
Right then, we can determine
1. we need to always beat sw1 & sw4 that wont ever be any vlan's root
2. we can use spanning-tree vlan 1,3,5 root primary on sw2 and
spanning-tree vlan 2,4,6 root secondary on sw 2 also (the opposite on sw3).
My other recommendation is don't let MST throw your for a loop. Each
instance's root port selection is tweaked with the
spanning-tree mst 2,4 cost 250 (notice its per INSTANCE)
spanning-tree mst 2,4 port-priority 0 (notice its per INSTANCE)
Whereas the non-MST commands are per vlan for the same thing.
_____
From: slevin kremera [mailto:slevin.kremera@gmail.com]
Sent: Wednesday, October 03, 2007 7:45 PM
To: Rich Collins
Cc: Cisco certification; Joseph Brunner; Brian Dennis
Subject: Re: mst priority
that was my second doubt too
joe /Brian ur thoughts
On 10/3/07, Rich Collins <nilsi2002@gmail.com > wrote:
I would say your first choice is easier and cleaner if you are allowed to
configure on both switches. I would use the second method if you are not
allowed to touch one switch and have to then modify cost or port-priority.
Actually I have a question to the first method.
It is preferable to set priority 0 or set to root?
Rich
On 9/29/07, slevin kremera <slevin.kremera@gmail.com> wrote:
There is a mst configuration between sw1-sw2-sw3 and there are 2
instances.Also there is etherchannel pagp configured between these 3
instance 1 13-14-15
instance 2 16-17-18..........
i want instance 1 to take one etherchannel and instance 2 to take
other.Myconfusion is..shud i set spanning-tree mst 1 priorty 0 on sw1
and instance 2
priority 0 on switch 2
or
go to etherchannel 1 in sw1 and set instance 1 with lower priority
goto etherchannel 2 in sw1 and set instance 2 with lower priority
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