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WITCH
6-50
RSTP
The Spanning Tree Algorithm (STA) can be used to detect and disable
network loops, and to provide backup links between switches, bridges or
routers. This allows the switch to interact with other bridging devices (that
is, an STA-compliant switch, bridge or router) in your network to ensure
that only one route exists between any two stations on the network, and
provide backup links which automatically take over when a primary link
goes down.
STA uses a distributed algorithm to select a bridging device
(STA-compliant switch, bridge or router) that serves as the root of the
spanning tree network. It selects a root port on each bridging device
(except for the root device) which incurs the lowest path cost when
forwarding a packet from that device to the root device. Then it selects a
designated bridging device from each LAN which incurs the lowest path
cost when forwarding a packet from that LAN to the root device. All ports
connected to designated bridging devices are assigned as designated ports.
After determining the lowest cost spanning tree, it enables all root ports
and designated ports, and disables all other ports. Network packets are
therefore only forwarded between root ports and designated ports,
eliminating any possible network loops.
Once a stable network topology has been established, all bridges listen for
Hello BPDUs (Bridge Protocol Data Units) transmitted from the Root
Bridge. If a bridge does not get a Hello BPDU after a predefined interval
(Maximum Age), the bridge assumes that the link to the Root Bridge is
down. This bridge will then initiate negotiations with other bridges to
reconfigure the network to reestablish a valid network topology.
RSTP (Rapid Spanning Tree Protocol, IEEE 802.1w) is designed as a
general replacement for the slower, legacy Spanning Tree Protocol (STP,
IEEE 802.1D). RSTP achieves much faster reconfiguration (i.e., around 1
to 3 seconds, compared to 30 seconds or more for STP) by reducing the
number of state changes before active ports start learning, predefining an
Summary of Contents for GSW-1676
Page 1: ...GSW 1676 GSW 2476 User Manual...
Page 2: ......
Page 16: ...FIGURES xvi...
Page 58: ...CONFIGURING THE SWITCH 6 10 Figure 6 3 Status Overview...
Page 62: ...CONFIGURING THE SWITCH 6 14 Web Click STATUS Statistics Figure 6 4 Port Statistics...
Page 71: ...STATIC MAC 6 23 Figure 6 13 Counter Configuration...
Page 109: ...802 1X 6 61 Figure 6 32 802 1X Configuration...
Page 113: ...802 1X 6 65 Web Click 802 1X Statistics Figure 6 33 802 1X Statistics...
Page 128: ...TROUBLESHOOTING A 4...
Page 138: ...SPECIFICATIONS C 4...
Page 144: ...GLOSSARY Glossary 6...
Page 148: ...INDEX Index 4...
Page 149: ......
Page 150: ...GSW 1676 GSW 2476 E052010 CS R02 149100011100H...