Spanning tree on new switch stack

[bravenet12]

I am about rip and replace my current 3750G stack with a 3750X stack. I have trunked over vlan and vtp info and implemented a config so it should be ready to go other then moving cables onto it. However one thing I want to correct with our current setup is that the root bridge on our vlans including vlan 1 is on a separate set of switches that we control, however I would like this new stack to be the root bridge for all of our vlans. It will be the central set of switches that all other switches trunk into.  I have pre-set higher spanning-tree priorities for each vlan on the new stack so I expect as I move lines into it that the tree will be re-calculated with it as the root bridge. I've ensured that there are no root guards on any of the other switches trunks and priorities are all at default levels for each vlan. Should I enforce root guard on the trunk interfaces of the new master stack?  Most of the trunks are port-channels to the other switches - do I need to set root guard on the Port channel interface or on the individual ports that make up the Port channel? On both? Any other recommendations in regards to implementing spanning-tree with the new stack? I know using port channels eliminates a lot of potential for loops but not every trunk is and I'd still like to have spanning-tree on. Thanks

[Reza Sharifi · Accepted solution]

root guard needs to be enabled on the physical interface that make up the Portchannel.

have a look at the config duide.  I did not find a good explanation in the config guid for the 3750, so this document is for 6500 series.

Loop guard uses the ports known to spanning tree.  Loop guard can take advantage of logical ports provided by the Port  Aggregation Protocol (PAgP). However, to form a channel, all the  physical ports grouped in the channel must have compatible  configurations. PAgP enforces uniform configurations of root guard or  loop guard on all the physical ports to form a channel.

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/stp_enha.html#wp1036858

HTH