About Spaning Tree configuration and switch backbone performance

[asanes]

Hello,, there is a backbone of catalyst 5000 swicth, there are more than 15 vlans conigured in that backbone. Recently, I was looking for all stp configurations for each vlan, what i found was that not all switchs in the backbone(all 5 switchs are connected via trunk) has all vlans configured, i also have some problems in finding the root bridge for some vlans, even in one vlan there were 2 root bridge. the commands i used to find out the stp info were: sh spant (vlan #), sh spant summary. How can i find the root bridge for the remaining vlans?, isn´t neccesary that all switchs in the backbone has the same vlans configured?. Another doubth i have is that for some vlans the root bridge is a switch that has no ports connectad in that vlan, plus, the only switch in the backbnone that has ports connected to that vlan has a neighbor switch that has one port bloqued,, how much can i improve the performance of the switching network changing the root switch to the switch connected to the vlan???

Thanks ahead for all of your recommendations,,

[steve.barlow]

To help you troubleshoot, before any failures occur, map out your STP domain, roots, and blocked ports. It will save you tons of time when something fails. You can't really do this when something is going wrong, you need that info before hand. Understanding data flows before and after a failure is critical.

Go to a switch that has all vlans and do the sh spant (vlan #), if a switch doesn't have the vlan you are looking for, go to a switch that does. Map who is root for each vlan. Ideally your core switches should have all vlans for failover, but depending on your design it may not be required (i.e. if layer 3 routing can work around failures).

Without seeing your design and configs, generally I would set two switches as the STP root (set spant root ...), one froot or even numbered vlans and secondary root for odd numbered vlans and the other one root for odd numbered vlans and secondary for even numbered vlans. If HSRP is involved, make sure the HSRP active router is closely connected to the STP root for that vlan. STP and HSRP should always be closely tied. Most efficient traffic flow this way. Make sure they have all vlans configured on them and that all core switches are connected into them. This makes it easier to map out which ports are blocked and traffic flows, and in the even of failure, you can know how the data will flow. All other switches should be connected to each root (may even be channeled depending on port density issues) in case of failure.

Hope it helps.

Steve