Datasheet

 2017 Microchip Technology Inc. DS00002335B-page 27
KSZ8863MLL/FLL/RLL
3.6 Rapid Spanning Tree Support
There are three operational states of the Discarding, Learning, and Forwarding assigned to each port for RSTP:
Discarding ports do not participate in the active topology and do not learn MAC addresses.
Discarding state: The state includes three states of the disable, blocking, and listening of STP.
Port setting: “transmit enable = 0, receive enable = 0, learning disable = 1"
Software action: The processor should not send any packets to the port. The switch may still send specific packets to
the processor (packets that match some entries in the static table with “overriding bit” set), and the processor should
discard those packets. When disabling the port’s learning capability (learning disable=’1’), set the register 2 bit 5 and bit
4 flushes rapidly the port related entries in the dynamic MAC table and static MAC table.
Note: The processor is connected to port 3 via the MII interface. Address learning is disabled on the port in this state.
Ports in Learning states learn MAC addresses, but do not forward user traffic.
Learning state: Only packets to and from the processor are forwarded. Learning is enabled.
Port setting: “transmit enable = 0, receive enable = 0, learning disable = 0”
TABLE 3-12: SPANNING TREE STATES
Disable State Port Setting Software Action
The port should not for-
ward or receive any pack-
ets. Learning is disabled.
“transmit enable = 0,
receive enable = 0,
learning disable =1”
The processor should not send any packets to the port. The
switch may still send specific packets to the processor (packets
that match some entries in the “static MAC table” with “overrid-
ing bit” set) and the processor should discard those packets.
Address learning is disabled on the port in this state.
Blocking State Port Setting Software Action
Only packets to the pro-
cessor are forwarded.
Learning is disabled.
“transmit enable = 0,
receive enable = 0,
learning disable =1”
The processor should not send any packets to the port(s) in
this state. The processor should program the “Static MAC
table” with the entries that it needs to receive (for example,
BPDU packets). The “overriding” bit should also be set so that
the switch will forward those specific packets to the processor.
Address learning is disabled on the port in this state.
Listening State Port Setting Software Action
Only packets to and from
the processor are for-
warded. Learning is dis-
abled.
“transmit enable = 0,
receive enable = 0,
learning disable =1”
The processor should program the “Static MAC table” with the
entries that it needs to receive (for example, BPDU packets).
The “overriding” bit should be set so that the switch will forward
those specific packets to the processor. The processor may
send packets to the port(s) in this state. See Section 3.7, "Tail
Tagging Mode" for details. Address learning is disabled on the
port in this state.
Learning State Port Setting Software Action
Only packets to and from
the processor are for-
warded. Learning is
enabled.
“transmit enable = 0,
receive enable = 0,
learning disable = 0”
The processor should program the “Static MAC table” with the
entries that it needs to receive (for example, BPDU packets).
The “overriding” bit should be set so that the switch will forward
those specific packets to the processor. The processor may
send packets to the port(s) in this state. See Section 3.7, "Tail
Tagging Mode" for details. Address learning is enabled on the
port in this state.
Forwarding State Port Setting Software Action
Packets are forwarded and
received normally. Learn-
ing is enabled.
“transmit enable = 1,
receive enable = 1,
learning disable = 0”
The processor programs the “Static MAC table” with the entries
that it needs to receive (for example, BPDU packets). The
“overriding” bit is set so that the switch forwards those specific
packets to the processor. The processor can send packets to
the port(s) in this state. See Section 3.7, "Tail Tagging Mode"
for details. Address learning is enabled on the port in this state.