User’s Manual of NS2503-24P/2C
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4.8 Spanning Tree Protocol
4.8.1 Theory
The Spanning Tree protocol can be used to detect and disable network loops, and to provide backup links between switches,
bridges or routers. This allows the switch to interact with other bridging devices in your network to ensure that only one route
exists between any two stations on the network, and provide backup links which automatically take over when a primary link
goes down. The spanning tree algorithms supported by this Managed Switch include these versions:
STP – Spanning Tree Protocol (IEEE 802.1D)
MSTP – Multiple Spanning Tree Protocol (IEEE 802.1s)
STP
- The Spanning Tree Protocol (STP) is a standardized method (
IEEE 802.1D
) for avoiding loops in switching networks.
Enable STP to ensure that only one path at a time is active between any two nodes on the network.
MSTP
- The Multiple Spanning Tree Protocol (MSTP) is a standardized method (
IEEE 802.1S
) for providing simple and full
connectivity for frames assigned to any given VLAN throughout a Bridged Local Area Network comprising arbitrarily
interconnected Bridges, each operating MSTP, STP , or RSTP. MSTP allows frames assigned to different VLANs to follow
separate paths, each based on an independent
Multiple Spanning Tree Instance (MSTI)
, within
Multiple Spanning Tree
(MST)
Regions composed of LANs and or MST Bridges. These Regions and the other Bridges and LANs are connected into a
single
Common Spanning Tree (CST)
.
The
IEEE 802.1D Spanning Tree
Protocol and
IEEE 802.1s Multiple Spanning Tree
Protocol allow for the blocking of links
between switches that form loops within the network. When multiple links between switches are detected, a primary link is
established. Duplicated links are blocked from use and become standby links. The protocol allows for the duplicate links to be
used in the event of a failure of the primary link. Once the Spanning Tree Protocol is configured and enabled, primary links are
established and duplicated links are blocked automatically. The reactivation of the blocked links (at the time of a primary link
failure) is also accomplished automatically without operator intervention.
This automatic network reconfiguration provides maximum uptime to network users. However, the concepts of the Spanning
Tree Algorithm and protocol are a complicated and complex subject and must be fully researched and understood. It is possible
to cause serious degradation of the performance of the network if the Spanning Tree is incorrectly configured. Please read the
following before making any changes from the default values.
The Switch STP performs the following functions:
Creates a single spanning tree from any combination of switching or bridging elements.
Creates multiple spanning trees – from any combination of ports contained within a single switch, in user specified
groups.
Automatically reconfigures the spanning tree to compensate for the failure, addition, or removal of any element in
the tree.
Reconfigures the spanning tree without operator intervention.
