Rapid Spanning Tree - Hirschmann PowerMICE User Manual

Rapid Spanning Tree

1 Rapid Spanning Tree
Note: The Spanning Tree protocol and the Rapid Spanning Tree protocol are
protocols for MAC bridges. They are described in the standards IEEE
802.1D-2004 and IEEE 802.1w. For this reason, the following description of
these protocols usually employs the term bridge instead of switch.
Local area networks are becoming ever larger. This is true both for their geo-
graphic size as well as for the number of stations they include. As the net-
works become larger, there are reasons why it often makes sense to imple-
ment several bridges:
D
reduce network load in subnetworks,
D
create redundant connections and
D
overcome distance.
Using many bridges with multiple, redundant connections between the sub-
networks can lead to loops and thus to the complete failure of the network.
The (Rapid) Spanning Tree Algorithm was developed to prevent this. The
Rapid Spanning Tree Protocol (RSTP) enables redundancy by interrupting
loops.
RSTP is a further development of the Spanning Tree Protocol (STP) and is
compatible with it. If a connection or a bridge fails, the STP requires up to 30
seconds to reconfigure. This was no longer acceptable in time-sensitive ap-
plications. The STP was therefore developed into the RSTP, leading to re-
configuration times of less than a second.
Note: The standard demands that all bridges of a network have to work with
the (Rapid) Spanning Tree Algorithm. If, however, both protocols are used
simultaneously, there are no advantages to using the faster reconfiguration
with RSTP.
Redundancy L3P
Release 3.0 01/07
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