Loop scenarios

A loop is present on the network. A number of scenarios can be seen:

• The switches are powered up and stable. STP has logically removed all loops. CobraNet devices are then powered up. No loop effects will be seen.
• CobraNet devices are powered up and stable. One or more switches are powered up (or powered down then up). A momentary data storm may occur long enough to cause CM-1 failures.
• A network topology, such as either of the examples in the Commonly used fault tolerant techniques for CobraNet networks section, is in use and functioning properly with redundant links having been removed by STP. A link between switches is then broken. STP creates a new path and the network continues to work properly. Later, the bad link is repaired. When the link is reestablished, a loop is momentarily created until STP removes it.
• Rapid Spanning Tree (RSTP) is a newer variant of Spanning Tree (STP) in which management of the links is accomplished an order of magnitude faster than standard Spanning Tree. The net effect of this operating characteristic is that a network using RSTP can experience data storm like events in the course of its normal operation while resolving loops.