Table of Contents
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RUGGEDCOM ROX II
CLI User Guide
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Section 5.36.1, "RSTP Operation"
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Section 5.36.2, "RSTP Applications"
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Section 5.36.3, "MSTP Operation"
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Section 5.36.4, "Configuring STP Globally"
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Section 5.36.5, "Configuring STP for Switched Ethernet Ports and Ethernet Trunk Interfaces"
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Section 5.36.6, "Managing Multiple Spanning Tree Instances Globally"
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Section 5.36.7, "Managing Multiple Spanning Tree Instances Per-Port"
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Section 5.36.8, "Viewing the Status of RSTP"
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Section 5.36.9, "Viewing RSTP Per-Port Statistics"
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Section 5.36.10, "Clearing Spanning Tree Protocol Statistics"
Section 5.36.1
RSTP Operation
The IEEE 802.1D Spanning Tree Protocol (STP) was developed to enable the construction of robust networks
that incorporate redundancy while pruning the active topology of the network to prevent loops. While STP is
effective, it requires that frame transfer halt after a link outage until all bridges in the network are guaranteed to be
aware of the new topology. Using the values recommended by IEEE 802.1D, this period lasts 30 seconds.
The Rapid Spanning Tree Protocol (RSTP), first introduced by IEEE 802.1w and significantly improved in IEEE
802.12D-2004, was a further evolution of the IEEE 802.1D Spanning Tree Protocol. It replaced the settling
period with an active handshake between bridges that guarantees the rapid propagation of topology information
throughout the network.
The following sections further describe the operation of RSTP:
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Section 5.36.1.1, "RSTP States and Roles"
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Section 5.36.1.2, "Edge Ports"
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Section 5.36.1.3, "Point-to-Point and Multipoint Links"
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Section 5.36.1.4, "Path and Port Costs"
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Section 5.36.1.5, "Bridge Diameter"
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Section 5.36.1.6, "eRSTP"
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Section 5.36.1.7, "Fast Root Failover"
Section 5.36.1.1
RSTP States and Roles
RSTP bridges have roles to play, either root or designated. One bridge - the Root Bridge - is the logical center of
the network. All other bridges in the network are Designated bridges. RSTP also assigns each port of the bridge
a state and a role. The RSTP state describes what is happening at the port in relation to address learning and
frame forwarding. The RSTP role basically describes whether the port is facing the center or the edges of the
network and whether it can currently be used.
RSTP Operation
Chapter 5
Setup and Configuration
513
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