Planet IGSW-2840, User Manual

Page: 155 / 671

User’s Manual of IGSW-2840
155
Fast Ethernet link (default port cost = 200,000). Gigabit ports could be used, but the port cost should be increased from the
default to ensure that the link between switch B and switch C is the blocked link.
4.7.1 STA
STP uses a distributed algorithm to select a bridging device (STP-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.
RSTP is designed as a general replacement for the slower, legacy STP. RSTP is also incorporated into MSTP. RSTP achieves
must faster reconfiguration (i.e., around one tenth of the time required by STP) by reducing the number of state changes before
active ports start learning, predefining an alternate route that can be used when a node or port fails, and retaining the forwarding
database for ports insensitive to changes in the tree structure when reconfiguration occurs.
4.7.1.1 Spanning Tree Information
STA Information
This screen displays a summary of the current bridge STA information that applies to the entire Industrial Managed Switch using
the STP Information screen..
Figure 4-7-1 STA Information screenshot
The page includes the following fields:
Object Description
•
Spanning Tree State
Shows if the Industrial Managed Switch is enabled to participate in an
STA-compliant network.