Prevention of broadcast storms by setting threshold values to high or low discards excessive broadcast, multicast, or unicast MAC traffic. In addition, configuration of values for rising thresholds on a switch will shut the port down.

STP problems include broadcast storms, loops, dropped BPDUs and packets. The function of STP is to ensure that no logic loops occur in a network by designating a root bridge. The root bridge is the central point of a spanning-tree configuration that controls how the protocol operates.

The location of the root bridge in the extended router and switch is necessary for effective troubleshooting. The show commands on both the router and the switch can display root-bridge information. Configuration of root bridge timers set parameters for forwarding delay or maximum age for STP information. Manually configuring a device as a root bridge is another configuration option.

If the extended router and switch network encounters a period of instability, it helps to minimize the STP processes occurring between devices.

If it becomes necessary to reduce BPDU traffic, put the timers on the root bridge at their maximum values. Specifically, set the forward delay parameter to the maximum of 30 seconds, and set the max_age parameter to the maximum of 40 seconds.

A physical port on a router or switch may be part of more than one spanning tree if it is a trunk.

Note: VTP runs on Catalyst switches not routers.

It is advisable to configure a Catalyst switch neighboring a router to operate in VTP transparent mode until Cisco supports VTP on its routers.

The Spanning-Tree Protocol (STP) is considered one of the most important Layer 2 protocols on the Catalyst switches.  By preventing logical loops in a bridged network, STP allows Layer 2 redundancy without generating broadcast storms.

Minimize spanning-tree problems by actively developing a baseline study of the network.

Web Links VLAN Tech Notes http://www.cisco.com/en/US/tech/ tk389/tk689/tech_tech_notes_list.html