Avaya C360 Manager, Installation And Configuration Manual

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Spanning Tree Protocol
Issue 2 July 2005 131
Spanning Tree Protocol
Overview
C360 switches support both common Spanning Tree protocol (802.1d) and the enhanced Rapid
Spanning Tree protocol (802.1w). IEEE 802.1w is a faster and more sophisticated version of the
802.1d (STP) standard. Spanning Tree makes it possible to recover connectivity after an outage
within a minute or so. RSTP, with its "rapid" algorithm, can restore connectivity to a network
where a backbone link has failed in much less time.
In order to configure the switch to either common Spanning Tree or Rapid Spanning Tree
protocol, use the
set spantree version
CLI command.
Spanning Tree Protocol
The Spanning Tree Algorithm ensures the existence of a loop-free topology in networks that
contain parallel bridges. A loop occurs when there are alternate routes between hosts. If there is
a loop in an extended network, bridges may forward traffic indefinitely, which can result in
increased traffic and degradation in network performance.
The Spanning Tree Algorithm:
●
Produces a logical tree topology out of any arrangement of bridges. The result is a single
path between any two end stations on an extended network.
●
Provides a high degree of fault tolerance. It allows the network to automatically reconfigure
the spanning tree topology if there is a bridge or data-path failure.
The Spanning Tree Algorithm requires five values to derive the spanning tree topology. These
are:
1. A multicast address specifying all bridges on the extended network. This address is
media-dependent and is automatically determined by the software.
2. A network-unique identifier for each bridge on the extended network.
3. A unique identifier for each bridge/LAN interface (a port).
4. The relative priority of each port.
5. The cost of each port.
After these values are assigned, bridges multicast and process the formatted frames (called
Bridge Protocol Data Units, or BPDUs) to derive a single, loop-free topology throughout the
extended network. The bridges exchange BPDU frames quickly, minimizing the time that
service is unavailable between hosts.