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KSZ8765CLXCC View Datasheet(PDF) - Micrel

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KSZ8765CLXCC Datasheet PDF : 153 Pages
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Micrel, Inc.
KSZ8765CLX
Functional Overview: Switch Core
The internal look-up table stores MAC addresses and their associated information. It contains a 1k unicast address table
plus switching information. The KSZ8765CLX is guaranteed to learn 1k addresses and distinguishes itself from a hash-
based look-up table, which, depending on the operating environment and probabilities, may not guarantee the absolute
number of addresses it can learn.
Learning
The internal look-up engine updates its table with a new entry if the following conditions are met:
The received packet’s source address (SA) does not exist in the look-up table.
The received packet is good; the packet has no receiving errors and is of legal length.
The look-up engine inserts the qualified SA into the table, along with the port number and time stamp. If the table is full
then the last entry of the table is deleted first to make room for the new entry.
Migration
The internal look-up engine also monitors whether a station is moved. If this occurs, it updates the table accordingly.
Migration happens when the following conditions are met:
The received packet’s SA is in the table, but the associated source port information is different.
The received packet is good; the packet has no receiving errors and is of legal length.
The look-up engine will update the existing record in the table with the new source port information.
Aging
The look-up engine will update the time stamp information of a record whenever the corresponding SA appears. The time
stamp is used in the aging process. If a record is not updated for a period of time, the look-up engine will remove the
record from the table. The look-up engine constantly performs the aging process and will continuously remove aging
records. The aging period is 300 ±75 seconds. This feature can be enabled or disabled through Register 3 bit [2].
Forwarding
The KSZ8765CLX will forward packets using an algorithm that is depicted in the following flowcharts. The next figure
shows stage one of the forwarding algorithm where the search engine looks up the VLAN ID, static table, and dynamic
table for the destination address, and then comes up with port to forward 1 (PTF1). PTF1 is then further modified by the
spanning tree, IGMP snooping, port mirroring, and port VLAN processes and authentication to come up with port to
forward 2 (PTF2), as shown in the figure below. The authentication and ACL have highest priority in the forwarding
process, ACL result will overwrite the result of the forwarding process. This is where the packets will be sent.
The KSZ8765CLX will not forward the following packets:
Error packets: These include framing errors, frame check sequence (FCS) errors, alignment errors, and illegal size
packet errors.
IEEE 802.3x PAUSE frames: KSZ8765CLX intercepts these packets and performs full-duplex flow control
accordingly.
Local packets: Based on destination address (DA) lookup, if the destination port from the look-up table matches the
port from which the packet originated, the packet is defined as local.
July 23, 2014
28
Revision 1.0
 

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