Spanning Tree Protocol Configuration; Mstp Global Configuration - Intellinet 561433 User Manual

User Manual

SPANNING TREE PROTOCOL CONFIGURATION

MSTP GLOBAL CONFIGURATION

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. It also provides
backup links, which automatically take over when a primary link goes down. The spanning tree algorithms
supported by this switch include these versions:
• STP – Spanning Tree Protocol (IEEE 802.1D)
• RSTP – Rapid Spanning Tree Protocol (IEEE 802.1w)
• MSTP – Multiple Spanning Tree Protocol (IEEE 802.1s)
The IEEE 802.1D Spanning Tree Protocol and IEEE 802.1w Rapid 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 to network performance 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.
BRIDGE PROTOCOL DATA UNITS
For STP to arrive at a stable network topology, the following information is used:
• The unique switch identifier
• The path cost to the root associated with each switch port
• The port identifier
STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU
contains the following information:
• The unique identifier of the switch that the transmitting switch currently believes is the root switch
• The path cost to the root from the transmitting port
• The port identifier of the transmitting port
The switch sends BPDUs to communicate and construct the spanning-tree topology. All switches connected
to the LAN on which the packet is transmitted will receive the BPDU. BPDUs are not directly forwarded by the
switch, but the receiving switch uses the information in the frame to calculate a BPDU, and, if the topology
changes, initiates a BPDU transmission.
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