KSZ9563RNXC-TR datasheet(36/226 Pages) MICROCHIP

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KSZ9563R

DS00002419D-page 36

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4.4.7

RAPID SPANNING TREE SUPPORT

There are three operational states assigned to each port for the Rapid Spanning Tree Protocol (RSTP):

Discarding State

Learning State

Forwarding State

4.4.7.1

Discarding State

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 host 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 pro-

cessor should discard those packets. When the port's learning capability (learning disable = '1') is disabled, port

related entries in the ALU table and static MAC table can be rapidly flushed.

4.4.7.2

Learning State

Ports in “learning state” learn MAC addresses, but do not forward user traffic.

• Learning State: Only packets to and from the host processor are forwarded. Learning is enabled.

• Port setting for Learning State: transmit enable = “0”, receive enable = “0”, learning disable = “0”.

• Software action: The processor should program the Static Address Table with the entries that it needs to receive

(e.g., 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 4.4.9, "Tail Tagging Mode"

for details). Address learning is enabled on the port in this state.

4.4.7.3

Forwarding State

Ports in “forwarding states” fully participate in both data forwarding and MAC learning.

• Forwarding state: Packets are forwarded and received normally. Learning is enabled.

• Port setting: transmit enable = “1”, receive enable = “1”, learning disable = “0”.

• Software action: The host processor should program the Static Address Table with the entries that it needs to

receive (e.g., BPDU packets). The “overriding” bit should be set so that the switch will forward those specific pack-

ets to the processor. The processor may send packets to the port(s) in this state (see Section 4.4.9, "Tail Tagging

Mode" for details). Address learning is enabled on the port in this state.

RSTP uses only one type of BPDU called RSTP BPDUs. They are similar to STP configuration BPDUs with the excep-

tion of a type field set to “version 2" for RSTP and “version 0" for STP, and a flag field carrying additional information.

Learning State

Port Setting

Software Action

Only packets to and from the

processor are forwarded.

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. Address learning

is enabled on the port in this state.

Forwarding State

Port Setting

Software Action

Packets are forwarded and

received normally.

Learning 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 proces-

sor. The processor can send packets to the port(s) in

this state. Address learning is enabled on the port in

this state.

TABLE 4-12:

SPANNING TREE STATES (CONTINUED)

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