Allied Telesis SwitchBlade x3100 Series Manual page 384

Introduction
TABLE 4-11
State
Forwarding
Disable
Excluded
For Rapid STP (explained in 4.5.3.5), the "blocking" and "listening" states shown above are combined
Note:
into a single "discarding" state
4.5.3.4 Convergence
The process by which the switches in the extended LAN come to agreement about the logical spanning tree
topology is known as convergence. This process includes several key steps:
The switches set their ports to the listening state. They elect a root bridge by exchanging hello messages to
•
determine which switch has the lowest bridge ID.
The root bridge initiates calculation of root path costs. Each switch uses information received from other
•
switches, along with its own port cost information, to compute its own root path cost. It forwards this cost
information along to other switches; eventually, the correct root path cost for every path in the extended
LAN will be computed.
Each switch elects a root port for that switch.
•
The switches elect a designated bridge for each physical LAN, based on the root path cost for the switches
•
Any port that is determined not to be a root port or a designated port is set to the blocking state.
•
After the expiration of forwarding delay timers, every root port and designated port is set to the forward-
•
ing state. Once this is done, traffic may flow over the extended LAN, without any network loops being
present.
If a link or switch fails, or the network topology otherwise changes, the network starts the convergence pro-
cess again to reach a new spanning tree topology.
4-64
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
Spanning Tree Port States
Meaning
The normal state for a port. The port is
enabled and receiving and transmitting traffic
data frames as well as BPDUs, and is adding
source MAC address information for all
frames to the forwarding database.
No BPDUs are received or transmitted on the
port
Port has been removed from STP operations.
Spanning Tree Protocol (STP and RSTP)
Transition
The switch places ports into this
state upon expiration of a forwarding
delay timer while in the learning
state, unless something has caused
the port to be placed in the blocking
state.
The switch places ports into this
state based on manual actions.
When a port is originally designated
as taking part in STP, and is then
removed from STP, the port can have
a role of DESIGNATED and a state
of EXCLUDED.