KSZ9567RTXI datasheet(38/232 Pages) MICROCHIP

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KSZ9567R

DS00002329D-page 38

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• 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.

4.4.8

MULTIPLE SPANNING TREE SUPPORT

Multiple Spanning Tree Protocol (MSTP) is an extension of RSTP that allows different VLANs to have different spanning

tree configurations. The VLAN Table, Address Lookup Table and Static Address Table all contain a 3-bit field which can

be used to specify one of eight spanning trees. Each port contains state registers for specifying unique states for each

of the spanning trees.

4.4.9

TAIL TAGGING MODE

Tail tagging is a method to communicate ingress and egress port information between the host processor and the switch.

It is useful for spanning tree protocol, IGMP/MLD snooping, IEEE 1588, and other applications. As shown in Figure 4-

5, the tail tag is inserted at the end of the packet, between the payload and the 4-byte CRC / FCS.

When the switch forwards a received

packet to the host port, one tail tagging byte is added to the packet by the

switch to indicate to the host processor the port that the packet was received on. The format is shown in

Table 4-13

In the opposite direction, the host processor must add two tail tag bytes to each packet that it sends to the switch to

indicate the intended egress ports. When multiple priority queues are enabled, the tail tag is also used to indicate the

priority queue. The format is shown in Table 4-14

. This tail tag is removed by the switch before the packet leaves the

switch. If the Lookup bit (bit 10) is set, packet forwarding follows the standard forwarding process, and bits [9:0] are

ignored. When the Lookup bit is not set, bits [8:0] determine the forwarding ports and priority queue, while the Override

bit (bit 9) determines whether port blocking is overridden.

Tail tagging applies only to the host port, never to any other ports of the switch.

FIGURE 4-5:

TAIL TAG FRAME FORMAT

TABLE 4-13:

RECEIVE TAIL TAG FORMAT (FROM SWITCH TO HOST)

Bits

Description

PTP Message Indication

0 = Is not a PTP message. A 4-byte receive timestamp has not been added.

1 = Is a PTP message. A 4-byte timestamp has been added before the tail tag.

6:3

Reserved

2:0

Received Port

000 = Packet received at Port 1

001 = Packet received at Port 2

010 = Packet received at Port 3

011 = Packet received at Port 4

100 = Packet received at Port 5

101 = Packet received at Port 6

110 = Packet received at Port 7

DEST

ADDRESS

SOURCE

ADDRESS

802.1Q

TAG

(4)

ETYPE or

LENGTH

TAIL

TAG

2 (From Host)

1 (To Host)

PAYLOAD

46 (42) - 1500

FCS

BYTES

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