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STA operates at two levels, the Switch and the Port level. In
addition, STA uses several timers to periodically ensure the
integrity of switches/bridges and their ports in a network.
The following paragraphs introduce the key information and
terminology needed to understand the STA parameters. Please
note that the word “bridge” now refers to TE100-S55.
AT THE BRIDGE LEVEL
Root Bridge: A network must first establish a starting point
from which all data forwarding path values are calculated,
compared, and determined. The Root Bridge is the unit with the
lowest Bridge Identifier
1
(Bridge Priority + MAC address).
Bridge Priority: This is a user changeable parameter. This
parameter enables all bridges in the network to establish a Root
Bridge. A change to the Bridge Priority may cause the network to
re-establish a new Root Bridge. A high Bridge Priority increases
the chance for a bridge to be selected as the Root Bridge (the
smaller the number, the higher the priority).
Root Path Cost: From each bridge, Root Path Cost is the total
Path Cost of reaching the Root Bridge from a Designated Bridge.
A Root Bridge has Root Path Cost of 0.
Designated Bridge: From each LAN segment, the bridge that
has the lowest Root Path Cost to the Root Bridge becomes the
Designated Bridge. It forwards data packets for that LAN
segment. In case all bridges on a segment have the same Root
Path Cost, the bridge with the lowest Bridge Identifier becomes
the Designated Bridge.
1 The bridge MAC address is only used to decide the Root Bridge when
there are 2 or more bridges with the same Bridge Priority.