PT-7828 User’s Manual
Featured Functions
3-38
change. The main benefit of RSTP is that the configuration decision is made locally rather than
network-wide, allowing RSTP can carry out automatic configuration and restore a link faster than
STP.
STP Example
The LAN shown below has three segments, with adjacent segments connected using two possible
links. The various STP factors, such as Cost, Root Port, Designated Bridge Port, and Blocked Port
are shown in the figure.
y
Bridge A has been selected as the Root Bridge, since it was determined to have the lowest
Bridge Identifier on the network.
y
Since Bridge A is the Root Bridge, it is also the Designated Bridge for LAN segment 1. Port 1
on Bridge A is selected as the Designated Bridge Port for LAN Segment 1.
y
Ports 1 of Bridges B, C, X, and Y are all Root Ports sine they are nearest to the Root Bridge,
and therefore have the most efficient path.
y
Bridges B and X offer the same Root Path Cost for LAN segment 2. However, Bridge B was
selected as the Designated Bridge for that segment since it has a lower Bridge Identifier. Port
2 on Bridge B is selected as the Designated Bridge Port for LAN Segment 2.
y
Bridge C is the Designated Bridge for LAN segment 3, because it has the lowest Root Path
Cost for LAN Segment 3:
y
The route through Bridges C and B costs 200 (C to B=100, B to A=100)
y
The route through Bridges Y and B costs 300 (Y to B=200, B to A=100)
y
The Designated Bridge Port for LAN Segment 3 is Port 2 on Bridge C.
