Chapter 4. Web Configuration & Operation
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CHAPTER 4
WEB OPERATION & CONFIGURATION
Shutdown Port:
A loop-detected port is shutdown for a period of time configured in “Shutdown Time”.
Shutdown Port and Log:
A loop-detected port is shutdown for a period of time configured in “Shutdown Time”
and the event is logged.
Log Only:
The event is logged and the port remains enable.
Tx Mode:
Enable or disable a port to actively generate loop protection PDUs or to passively look for looped PDUs.
4.3.8 Spanning Tree
For some networking services, always-on connections are required to ensure that end users’ online related activities
are not interrupted due to unexpected disconnections. In these circumstances, multiple active paths between
network nodes are established to prevent disconnections from happening. However, multiple paths interconnected
with each other have a high tendency to cause bridge loops that make networks unstable and in worst cases make
networks unusable. For example, the MAC address table used by the switch or bridge can fail, since the same MAC
addresses (and hence the same network hosts) are seen on multiple ports. Second, a broadcast storm occurs. This is
caused by broadcast packets being forwarded in an endless loop between switches. A broadcast storm can consume
all available CPU resources and bandwidth.
To solve problems causing by bridge loops, spanning tree allows a network design to include redundant links to
provide automatic backup paths if an active link fails, without the danger of bridge loops, or the need for manually
enabling/disabling these backup links.
The Spanning Tree Protocol (STP), defined in the IEEE Standard 802.1s, can create a spanning tree within a mesh
network of connected layer-2 bridges (typically Ethernet switches) and disable the links which are not part of that tree,
leaving a single active path between any two network nodes.
To provide faster spanning tree convergence after a topology change, an evolution of the Spanning Tree Protocol
“Rapid Spanning Tree Protocol (RSTP)”, is introduced by IEEE 802.1w. RSTP is a refinement of STP; therefore, it shares
most of its basic operation characteristics. This essentially creates a cascading effect away from the root bridge where
each designated bridge proposes to its neighbors to determine if it can make a rapid transition. This is one of the
major elements which allows RSTP to achieve faster convergence times than STP.
The other extension of RSTP is IEEE 802.1s Multiple Spanning Tree protocol (MSTP) that allows different VLANs to
travel along separate instances of spanning tree. Unlike STP and RSTP, MSTP eliminates the needs for having different
STP for each VLAN. Therefore, in a large networking environment that employs many VLANs, MSTP can be more useful
than legacy STP.
Summary of Contents for MSW-4424C Series
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