Hi Rob, Remember that port priority is only evaluated if you have multiple ports that connect to the same "upstream" bridge. Root port selection uses the following preference:
1. Lowest root cost 2. If root cost through two bridges are equal, use lowest bridge ID 3. If bridge IDs are equal, use lowest port ID (mixture of port number and port priority) In your output, it sounds like Cat3 is the root. In that case, Cat1 won't care about the priorities advertised by Cat2. If you want Cat2 to be the root, you need to give it a lower bridge ID (MSTP priority) on the desired VLANs. If your goal was to make Cat1 go through Cat2 to reach the root Cat3, you could use port cost, but that would have to be done on Cat1. Also note that the "Prio" value shown in "sh spann" does NOT display the port priority of the incoming BPDUs. It displays the local priority shown in BPDUs sent OUT from the bridge that displays that output. If you look on Cat2, you should see the desired priority in "sh spann," or from Cat1 you can do a "sh spann interface fa0/24 detail" (I think... going from memory) and if BPDUs are being received on this port you should see the advertised port priority. Hope that helps, Bob On Fri, Feb 10, 2012 at 12:04 PM, Rob Tyrrell <[email protected]> wrote: > I am having an issue with port-priority influencing the root cost of its > downstream neighbor. I have configured the port-priority according to the > DSG on Cat2 Fa0/24: > > Cat2-MST(config-if)#do sh run int f0/24 > Building configuration... > > Current configuration : 107 bytes > ! > interface FastEthernet0/24 > switchport mode dynamic desirable > spanning-tree mst 0 port-priority 64 > End > > But Cat 1 still shows the secondary link to Cat3 as its root port, and > does not appear to have learned the preferred priority to Cat2. > > > Cat1-MST(config-if)#do sh span > > MST0 > Spanning tree enabled protocol mstp > Root ID Priority 24576 > Address 0018.baf8.5a80 > Cost 0 > Port 21 (FastEthernet0/21) > Hello Time 3 sec Max Age 15 sec Forward Delay 15 sec > > Bridge ID Priority 32768 (priority 32768 sys-id-ext 0) > Address 000b.be96.d800 > Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec > > Interface Role Sts Cost Prio.Nbr Type > ------------------- ---- --- --------- -------- > -------------------------------- > Fa0/1 Desg FWD 200000 128.1 P2p > Fa0/4 Desg FWD 200000 128.4 P2p > Fa0/5 Desg FWD 200000 128.5 P2p > Fa0/11 Desg FWD 2000000 128.11 Shr > Fa0/21 Root FWD 200000 128.21 P2p > Fa0/23 Altn BLK 200000 128.23 P2p > > Interface Role Sts Cost Prio.Nbr Type > ------------------- ---- --- --------- -------- > -------------------------------- > > Fa0/24 Altn BLK 200000 128.24 P2p > > I have shut/no shut all relevant interfaces, but still no change. I have > even removed and re-added the port-priority config on Cat2. > > Any ideas what I may be missing? > > Thanks, > > Rob > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
