Bridge Spanning Tree 5-11
Bridging
2. Type in the new Ageing Time, in seconds, then click on . The allowable
range is 10 to 1,000,000 seconds.
Bridge Spanning Tree
The Bridge Spanning Tree window allows you to display and modify the
9H42x-xx module’s bridge port information and protocol parameters relating to
the Spanning Tree Algorithm.
In a network design with multiple transparent bridges placed in parallel (i.e.,
attached to the same local network segment), only a single bridge should forward
data through the LAN, leaving the remaining bridges on the segment in a standby
state so that another can assume the bridging responsibility should the current
active bridge go down. The Spanning Tree Algorithm (STA) is the method that
bridges use to communicate with each other to ensure that only a single data
route exists between any two end stations.
In Transparent bridging, Spanning Tree must be used to prevent data loops (since
in an Ethernet environment, a packet propagated down multiple paths would
cause higher volumes of traffic and collisions that would cripple a network that
relies on carrier sense and collision detection). Spanning Tree selects a controlling
Root Bridge and Port for the entire bridged local area network, and a Designated
Bridge and Port for each individual network segment. The Root bridge is the one
that selects one of two or more available bridge paths between two end stations,
basing its decision on factors associated with each of the bridges in the path. A
Designated Port/Bridge for a network segment relays frames toward the Root
Bridge, or from the Root Bridge onto the network segment. When data passes
from one end station to another across a bridged local area network, it is
forwarded through the Designated Bridge/Port for each network segment
towards the Root Bridge, which in turn forwards frames towards Designated
Bridges/Ports on its opposite side.
During the Root Bridge selection process, all bridges on the network
communicate STA information via Bridge Protocol Data Units (BPDUs). It is with
BPDUs that the bridges collectively determine the current network topology and
ensure that all bridges have current topology information.
NOTE
Note that the Source Addresses Ageing Time is the same as the Ageing Time displayed
(and configured) via the Filtering Database window; setting the Ageing Time in the
Source Addresses window also changes the time in the Filtering Database window, and
vice versa.