KSZ9567RTXI-TR datasheet(30/232 Pages) MICROCHIP

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KSZ9567R

DS00002329D-page 30

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4.4.2.6

Aging

The lookup engine updates the age count information of a dynamic record in the ALU table whenever the corresponding

SA appears. The age count is used in the aging process. If a record is not updated for a period of time, the lookup engine

removes the record from the table. The lookup engine constantly performs the aging process and continuously removes

aging records. The aging period is about 300 seconds (±75 seconds) and can be configured longer or shorter (1 second

to 30 minutes). This feature can be enabled or disabled. Static entries are exempt from the aging process.

4.4.2.7

Forwarding

The device forwards packets using the algorithm that is depicted in Figure 4-3. Figure 4-3 shows stage one of the for-

warding algorithm where the search engine looks up the VLAN ID, static table, and dynamic table for the destination

address, and comes up with “port to forward 1" (PTF1). PTF1 is then further modified by spanning tree, IGMP snooping,

port mirroring, and port VLAN processes.

The ACL process works in parallel with the flow outlined above. The authentication and ACL processes have the highest

priority in the forwarding process, and the ACL result may override the result of the above flow. The output of the ACL

process is the final “port-to-forward 2" (PTF2) destination port(s).

The device will not forward the following packets:

• Error packets: These include framing errors, frame check sequence (FCS) errors, alignment errors, and illegal

size packet errors.

• MAC Control PAUSE frames: The device intercepts these packets and performs full duplex flow control accord-

ingly.

• “Local” packets: Based on destination address (DA) lookup. If the destination port from the lookup table matches

the port from which the packet originated, the packet is defined as “local”.

• In-Band Management packets.

FIGURE 4-3:

PACKET FORWARDING PROCESS FLOWCHART

Start

PTF1=NULL

VLAN ID Valid?

Get PTF1 from

Static Array

Static

Array

found

Get PTF1 from

Address Table

Address

Look-up

Table

found

Get PTF1 from

VLAN Table

PTF1

yes

not found

- Search VLAN table

- Ingress VLAN filtering

-Discard NPVID check

Search based on

DA or DA+FID

Search based on

DA+FID

PTF1

Spanning Tree

Process

Port Mirror

Process

IGMP / MLD

Process

PTF2

- Check receiving port s receive enable bit

- Check destination port s transmit enable bit

- Check whether packets are special (BPDU)

- IGMP / MLD packets are forwarded

to Host port

- Process does not apply to packets

received at Host port

-RX Mirror

-TX Mirror

- RX or TX Mirror

- RX and TX Mirror

Port

Authentication

& ACL

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