If I understand your topology correctly, switches 3 and 4 share an Ethernet segment. If I remember Spanning Tree correctly, one of these two will be the "designated bridge" for that segment. That bridge will be forwarding packets toward the root. All other bridges on that segment (in this case, the other switch) will block their link if it creates a loop.
I believe the designated bridge is the one on that segment with the lowest priority. If the priority is the same, the one with the lowest bridge ID (mac address) becomes the designated bridge. Changing the path cost on the link between 3 and 4 shouldn't have much affect on the switch that is the designated bridge - it will be forwarding anyway. Changing the path cost on the other switch should affect which of its links are forwarding and which are blocked. My guess is you don't have to actually change the path cost on both switches on floor 1 and floor 4. I think if you change the path cost on one of those two switches (the designated bridge) it actually won't have any affect (and thus you really don't need to...). You can also try setting which bridge is the designated one by making its priority lower than the other one - but DON'T make its priority lower than the root! Rob. CCIE 6922 ""steve skinner"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > guys, > > another question .. > > in on of my sites i have clusters of 3548 switches .. > At each end of the cluster i have a link to the distribution layer... > i have multiple uplink to each switch (6 in cluster).. > and in the middle we have set the spanning-tree cost on one interface of the > uplinks to much higher than default ...(that way switch 1 -3 use > distribution link 1 and switch 4-6 use distribution link 6 )..what i am > finding odd is that on switches 3 and 4 (the middle of my cluster) i have to > increase the cost on both switches`uplinks sometimes > and others just 1 switch, other times.(to force it into blocking)... > > floor 1 i had to do both > floor 2 just switch 3 > floor 4 both > floor 5 just switch 3 > floor 6 just switch 3 > > what i dont understand is why...??? > > i should have to set the uplink ports from 3 to 4 to > both having high costs ... > > why does it sometimes work with just one... > > any idea`s.. > > _________________________________________________________________ > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37879&t=37663 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
