Redundancy
HMG-838PT & HMG-838EPT Web Configuration 7-7
Loop Protection Status:
Port: The port number.
Action: Display the configured action that the switch will react when loops occur.
Transmit: Display the configured transmit (Tx) mode.
Loops: The number of loops detected on a port.
Status: The current loop status detected on a port.
Loop: Loops detected on a port or not.
Time of Last Loop: The time of the last loop event detected.
7-3 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 allow 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.
7-3.1 Bridge Settings
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