From: Tim (ccie2be@nyc.rr.com)
Date: Tue Sep 13 2005 - 19:37:29 GMT-3
Guys,
With all due respect, I disagree with this thinking.
I haven't tested it, so I won't comment on the effectiveness of using
port-priority on the upstream non-root switch relative to the downstream
switch.
But, I'm sure using cost on the downstream switch will work.
Actually, now that I think about it, I'm pretty sure using port priority
will also work even when neither switch is the root switch because if there
are more than one physical links between the 2 non root switches, STP still
has to determine which physical link to put in block state.
So, let's say you have this topology:
Sw1 sw2 sw3
And between each pair of switches there are multiple physical links. Lets
also assume that sw3 is elected the root switch. Then relative to the root
switch, sw2 is the upstream switch from sw1's point of view.
Now, how does STP decide which physical link between sw1 and sw2 should be
forwarding and which should be blocking?
Wouldn't it go through the exact same process that sw2 and sw3 did?
tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Ralph
Sent: Tuesday, September 13, 2005 5:54 PM
To: terry.francona@gmail.com
Cc: ccielab@groupstudy.com
Subject: Re: Load Balancing Across Trunks
Yes Anthony, if you do not have control or access to the root switch for a
vlan there is really very little you can do to load balance traffic for that
vlan. If etherchannel is not allowed, you can use the switchport trunk
allowed vlan command; But I'm not sure if this is fault-tolerant because it
is not a spanning tree feature.
Ralph.
-----Original Message-----
From: Anthony Sequeira <terry.francona@gmail.com>
To: Group Study <ccielab@groupstudy.com>
Date: Tue, 13 Sep 2005 17:28:31 -0400
Subject: Load Balancing Across Trunks
It seems to be a simple task to load balance traffic on a VLAN basis across
your trunk links if you are dealing with only two switches that you
completely control. For example, if you are forbidden from using port cost,
just make one of your two switches the root for all VLANs and then set the
port priorities apropriately on this upstream switch for each VLAN.
But what if the root of a VLAN you need to load balance is on a third
switch out of your control? Now you can play with port-priority all you want
on your two switches but your configurations will have no effect.
Must we be able to control the root switch election in order to properly
load balance across trunk links using port priority? I have "labbed" this up
- and it seems that we do need this level of control.
Is there another way to control load balancing across trunk links beyond
port cost and port priority? I think not.....
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