Peavey MediaMatrix NION Hardware Manual page 68

Appendix A - Troubleshooting
Many Ethernet switches contain some variant of the Spanning Tree Protocol (STP, RSTP or
MSTP) that detects and logically removes loops. Standard STP should not allow a connection
to be made until it is sure that the connection will not cause a loop. MSTP and RSTP can
behave a little differently. If a new connection is made through a port that the protocol
previously considered to be an edge port. (i.e. it cannot be connected to another switch), then
the port will be immediately enabled. If this connection is such that it can create a loop, then a
data storm can occur. Explicitly setting ports within an RSTP/MSTP managed switch to be
edge or bridge ports, per their usage, may alleviate this problem.
Commonly used fault tolerant techniques for CobraNet networks
Intentional creation of a loop, with reliance on STP to remove it, in order to create a spare
connection that will be automatically activated when a link in the network goes down.
Use of the primary and secondary Ethernet connections on a CobraNet interface along
with redundant and interconnected switches. Proper use of CobraNet DualLink with
redundant networks will intentionally create a loop that is automatically removed or
restored by STP.
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.
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