From: Anthony Sequeira (terry.francona@gmail.com)
Date: Wed Sep 14 2005 - 10:33:21 GMT-3
Lee - thanks for the confirmation of what I am seeing in my lab setup and
for your succinct reminder of how port-priority comes into play. Or in my
case - DOES NOT!
I will now play with port cost to practice how it can effect the
spanning-tree topology when I have a configuration like this!
Tim - it sounds like YOU might need to re-read the Cisco Press book
recommendation you gave us ;-)
On 9/14/05, Tim <ccie2be@nyc.rr.com> wrote:
>
> Anthony,
>
> I'd be very interested in seeing how you tested this.
>
> If your topology is like this:
>
> Root bridge --- sw1 ==== sw2
>
> Where there are multiple physical paths between sw1 and sw2, there must be
> someway that STP puts the redundant ports on sw2 into a blocked state and
> determines which port will forward.
>
> In your testing, what did you find was the way STP determined this?
>
> Tim
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Anthony Sequeira
> Sent: Wednesday, September 14, 2005 12:31 AM
> To: Group Study
> Subject: Re: Load Balancing Across Trunks
>
> I have confirmed through lab tests that you cannot use port-priority on
> two
> downstream switches from the root to control the choice of trunk port for
> the traffic.
> Certainly, as Tim suggested in this thread, if you use Root Guard to block
> the backbone device - you can then get yourself in a situation where you
> can
> use port-priority, since now you can control the election of the root
> device.
> I am waiting for someone to PROVE otherwise - but at this point - it looks
> like load-balancing using port-priority is only an option when one of the
> two switches you are trying to load balance between is the root!
>
> On 9/13/05, Anthony Sequeira <terry.francona@gmail.com> wrote:
> >
> > 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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