Transient phenomena in bridged local area networks

The transient behavior of the bridged LAN (local area network) following failures is described. It is noted that, in the presence of an intermittent failure, the bridged LAN may experience high transient traffic periods called storms as well as virtual-circuit disconnects. In most cases observed, storms last less than a hello time. The peak traffic on the LAN during the storm is proportional to the peak forwarding rates of the bridges connected to the LAN. Some storms may not remain as local problems but propagate towards other parts of the network. The presence of separate RDB (routing database) tables for each port increases the probability of virtual-circuit disconnects. Some virtual-circuit disconnect problems can be prevented by setting certain time-out values appropriately, but this solution has the disadvantage of masking component failures from the network manager. Other means to detect and reduce the frequency of storms and virtual-circuit disconnects are also suggested. These point to a need for better network management tools for bridged LANs.