RSTP convergence takes many seconds

Another myth is that RSTP convergence takes many seconds. In certain situations and with some equipment this may be true. However, some vendors are offering devices that will converge RSTP in sub-50ms with little to no planning or effort.

Advanced network planning may be required to achieve these speeds in certain situations, but it is possible with certain vendor's RSTP deployment. Problems with spanning tree in many instances arise from poor planning, design, and deployment. Spanning tree should be segmented and designed in small domains to be successful. A spanning tree domain is an area in which BPDUs will propagate.

While advanced features of MSTP can be utilized, so can building manual spanning tree domains with legacy RSTP by disabling or blocking BPDUs on certain planned segments. In this way you create domains of segments and rings where spanning-tree is enabled, and keep the segments manageable. It is also essential to chose a root bridge and backup root bridge carefully. Path-costs should be modified so that the network administrator knows exactly what will happen to the traffic in the event of a failed segment anywhere in the network.

December 17, 2011

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