Peavey MediaMatrix Nion Hardware Manual page 73


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.

A network topology, such as either of the examples in the Commonly used fault tolerant
techniques for CobraNet networks (on page 68) 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.
What we know

CobraNet modules can crash in the presence of excessive network traffic (data storms).

Excessive traffic is almost always caused by the presence of a loop but can, in some cases,
be a consequence of normal operation.

Loops, in conjunction with the use of Spanning Tree or an analogous feature such as
RSTP, MSTP or Meshing (a proprietary HP protocol), can be intentionally used to create
fault tolerant network topologies.

Different topologies can cause loop effects.

Loops and use of Spanning Tree will typically only apply to networks that use more than
one switch. Use of more than one switch is common.
Mitigation

Do not use topologies that intentionally employ loops when their use can be avoided.

Check for the presence of, and remove any, unintended loops.

Do not use Rapid Spanning Tree (RSTP or MSTP). Use STP.
June 11, 2012 Version 1.6.4b.1
NION Hardware Manual
69