CHAPTER 6: OPERATIONAL GUIDE
OPERATIONAL GUIDE
MULTINET4 MULTI-PORT SERIAL SERVER & MANAGED SWITCH – INSTRUCTION MANUAL
6–5
6.3
RSTP
The Rapid Spanning Tree Protocol (RSTP) constructs a system linking the elements of a
bridged local area network so as to supply redundancy, provide for quick recovery from
failure of a segment, and eliminate loops. The protocol can be said to be "spanning" in that
it connects all elements in the system and to be a "tree" in that it connects these elements
while remaining implicitly free of loops.
The original Spanning Tree Protocol (STP) was defined by IEEE standard 802.1D. The faster
RSTP was first defined in IEEE 802.1W and RSTP supersedes STP in IEEE 802.1D (2004). STP
consumes 45 to 60 seconds to recover from a failure because it needs to recalculate the
entire tree after a failure. RSTP can recover in less than one second because it enables
ports to actively communicate information about special conditions. Multinet4 supports
both protocols, so that you can configure a port to use the older STP if it is necessary to
accommodate a legacy bridge.
This appendix provides a high-level summary of the protocol to enable understanding of
your options in configuring RSTP. For a more detailed understanding see the freely
available IEEE 802.1D (2004) standard.
Access RSTP functionality in Multinet4 with the following screens:
•
Bridge: Global Settings, described in
section 4.4.2.1: Bridge: Global
Settings
.
•
RSTP: Port Settings, described in
section 4.4.3.2: RSTP: Port Settings
.
•
RSTP: Bridge Status, described in
section 4.4.3.3: RSTP: Bridge Status
.
•
RSTP: Port Status, described in
section 4.4.3.4: RSTP: Port Status
.
6.3.1
RSTP Setup
When first configured with RSTP the bridges in a system exchange messages with one
another to elect a
root bridge
and to discover the shortest path from each bridge to the
root bridge. The ports that enable the shortest paths are put into forwarding mode. All
other ports are assigned backup or alternate roles. When a stable tree has been
established and traffic is being transmitted the system is said to have achieved
convergence
.
