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260 Intel® Blade Server Ethernet Switch Module IXM5414E
Forwarding The port is forwarding packets. For additional information, see “Forwarding state”
on page 266.
Disabled The port responds only to network management messages and must return to the
discarding state first. For additional information, see
“Disabled state” on page 268.
Note that the STP port state of disabled applies only to the port’s role within the
spanning tree, and should not be confused with the port’s administrative state of
enabled or disabled.
A port changes from one state to another as follows:
• From initialization (switch startup) to discarding
• From discarding to learning or to disabled
• From learning to forwarding or to disabled
• From forwarding to disabled or to discarding
• From disabled to discarding
When you enable STP, every port on every bridge in the network goes through the discarding state
and then goes through the learning state at startup. If properly configured, each port stabilizes to the
forwarding or discarding state.
No packets (except BPDUs and LACPDUs) are forwarded from, or received by, STP enabled ports
until the forwarding state is enabled for that port.
IEEE 802.1w STP port states
The IEEE 802.1w protocol definition speeds up the reconfiguration of the spanning tree using two
new mechanisms:
• Bridges exchange explicit acknowledgement frames
• Ports may be configured to transition directly to the forwarding state when the bridge is
reinitialized – this is appropriate for edge ports
The number of port states were reduced from five to three, specified in the original IEEE 802.1D
standard:
Discarding The port is blocked from forwarding or receiving packets and does not add
information to the forwarding database.
Learning The port is adding addresses to its forwarding database but not yet forwarding
packets.
Forwarding The port is adding addresses to its forwarding database and is forwarding packets.
Table 12. Relationship between IEEE 802.1D and IEEE 802.1w port states
IEEE 802.1D port
state
Admin. bridge
port state
MAC operational
IEEE 802.1w port
state
Active topology port
role
Disabled Disabled False Discarding Excluded, disabled
Disabled Enabled False Discarding Excluded, disabled
Blocking Enabled True Discarding
Excluded, alternate or
backup