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The Switch supports Spanning Tree Protocol (STP), Rapid Spanning Tree Protocol (RSTP) and Multiple
Spanning Tree Protocol (MSTP) as defined in the following standards.
• IEEE 802.1D Spanning Tree Protocol
• IEEE 802.1w Rapid Spanning Tree Protocol
• IEEE 802.1s Multiple Spanning Tree Protocol
The Switch also allows you to set up multiple STP configurations (or trees). Ports can then be assigned to
the trees.
13.1 STP/RSTP Overview
(R)STP detects and breaks network loops and provides backup links between switches, bridges or
routers. It allows a Switch to interact with other (R)STP-compliant switches in your network to ensure that
only one path exists between any two stations on the network.
The Switch uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allows faster convergence of the
spanning tree than STP (while also being backwards compatible with STP-only aware bridges). In RSTP,
topology change information is directly propagated throughout the network from the device that
generates the topology change. In STP, a longer delay is required as the device that causes a topology
change first notifies the root bridge and then the root bridge notifies the network. Both RSTP and STP flush
unwanted learned addresses from the filtering database. In RSTP, the port states are Discarding,
Learning, and Forwarding.
Note: In this user's guide, "STP" refers to both STP and RSTP.
13.1.1 STP Terminology
The root bridge is the base of the spanning tree.
Path cost is the cost of transmitting a frame onto a LAN through that port. The Switch supports both the
short and the long path cost methods. The original short path cost method uses a 16-bit value. The long
path cost method allows the Switch to use longer path length (32-bit values) for high-speed links. The
default cost is assigned according to the speed of the link to which a port is attached. The slower the
media, the higher the cost.
Table 39 STP Path Costs
Path Cost
Path Cost
Spanning Tree Protocol
DEFAULT VALUE
LINK SPEED
(SHORT)
10Mbps
100
100Mbps
19
MES3500-24S/MGS3520 Series User's Guide
C
H A P T E R
DEFAULT VALUE
(LONG)
2,000,000
200,000
126
13
ALLOWED RANGE
1 to 200,000,000
1 to 200,000,000
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