System information

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4.3.6 Rapid Spanning Tree
The Spanning Tree Protocol (STP), defined in the IEEE Standard 802.1d, creates a
spanning tree within a mesh network of connected layer-2 bridges (typically Ethernet
switches) and prevents loops when you establish redundant links. Those links become
important when one of the links goes down.
As mentioned, multiple active paths between network nodes cause a bridge loop. Bridge
loops create several problems. First, 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.
Spanning tree allows a network design to include spare (redundant) links to provide
automatic backup paths if an active link fails, without the danger of bridge loops, or the need
for manually enabling or disabling these backup links.
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 with
document 802.1w. RSTP is a refinement of STP and 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.
Click the folder Rapid Spanning Tree from the Switch Management menu and then three
options within this folder will be displayed as follows.
1. RSTP Switch Settings: Set up system priority, max Age, hello time, etc.
2. RSTP Physical Port Settings: Set up physical, ability and edge status of port.