KSZ8873MLL_11 Datasheet, PDF (37/108 Pages) Micrel Semiconductor – Integrated 3-Port 10/100 Managed Switch with PHYs

Micrel, Inc.
KSZ8873MLL/FLL/RLL
Ingress to Port 3 (Host -> KSZ8873MLL/FLL/RLL)
Bit [1,0]
0,0
0,1
1,0
1,1
Bit [3,2]
0,0
0,1
1,0
1,1
Egress from Port 3 (KSZ8873MLL/FLL/RLL->Host)
Bit [0]
0
1
Destination Port
Normal (Address Look up)
Port 1
Port 2
Port 1 and 2
Frame Priority
Priority 0
Priority 1
Priority 2
Priority 3
Source Port
Port 1
Port 2
Figure 8. Tail Tag Rules
IGMP Support
For Internet Group Management Protocol (IGMP) support in layer 2, the KSZ8873MLL/FLL/RLL provides two
components:
IGMP Snooping
The KSZ8873MLL/FLL/RLL traps IGMP packets and forwards them only to the processor (port 3). The IGMP packets are
identified as IP packets (either Ethernet IP packets, or IEEE 802.3 SNAP IP packets) with IP version = 0x4 and protocol
version number = 0x2.
IGMP Send Back to the Subscribed Port
Once the host responds the received IGMP packet, the host should knows the original IGMP ingress port and send back
the IGMP packet to this port only, otherwise this IGMP packet will be broadcasted to all port to downgrade the
performance.
Enable the tail tag mode, the host will know the IGMP packet received port from tail tag bits [0] and can send back the
response IGMP packet to this subscribed port by setting the bits [1,0] in the tail tag. Enable “Tail tag mode” by setting
Register 3 bit 6. The tail tag will be removed automatically when the IGMP packet is sent out from the subscribed port.
Port Mirroring Support
KSZ8873MLL/FLL/RLL supports “Port Mirroring” comprehensively as:
“receive only” mirror on a port
All the packets received on the port are mirrored on the sniffer port. For example, port 1 is programmed to be
“receive sniff” and port 3 is programmed to be the “sniffer port”. A packet received on port 1 is destined to port 2
after the internal lookup. The KSZ8873MLL/FLL/RLL forwards the packet to both port 2 and port 3. The
KSZ8873MLL/FLL/RLL can optionally even forward “bad” received packets to the “sniffer port”.
“transmit only” mirror on a port
All the packets transmitted on the port are mirrored on the sniffer port. For example, port 1 is programmed to be
“transmit sniff” and port 3 is programmed to be the “sniffer port”. A packet received on port 2 is destined to port 1
after the internal lookup. The KSZ8873MLL/FLL/RLL forwards the packet to both port 1 and port 3.
“receive and transmit” mirror on two ports
All the packets received on port A and transmitted on port B are mirrored on the sniffer port. To turn on the “AND”
feature, set register 5 bit [0] to ‘1’. For example, port 1 is programmed to be “receive sniff”, port 2 is programmed
to be “transmit sniff”, and port 3 is programmed to be the “sniffer port”. A packet received on port 1 is destined to
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