Datasheet
2017 Microchip Technology Inc. DS00002348A-page 31
KSZ8873MLL/FLL/RLL
3.8 IGMP Support
For Internet Group Management Protocol (IGMP) support in layer 2, the KSZ8873MLL/FLL/RLL provides two compo-
nents: IGMP snooping and IGMP send-back to the subscribed port.
3.8.1 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 pro-
tocol version number = 0x2.
3.8.2 IGMP SEND-BACK TO THE SUBSCRIBED PORT
Once the host responds the received IGMP packet, the host should know the original IGMP ingress port and send back
the IGMP packet to this port only, otherwise this IGMP packet will be broadcasted to all ports to downgrade the perfor-
mance.
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.
3.9 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 port 2 after the internal lookup. The KSZ8873MLL/FLL/RLL forwards the packet to both port 2
and port 3.
Multiple ports can be selected as “receive sniff” or “transmit sniff”. In addition, any port can be selected as the “sniffer
port”. All these per port features can be selected through registers 17, 33, and 49 for ports 1, 2, and 3, respectively.
3.10 Rate Limiting Support
The KSZ8873MLL/FLL/RLL provides a fine resolution hardware rate limiting from 64 kbps to 99 Mbps. The rate step is
64 kbps when the rate range is from 64 kbps to 960 kbps and 1 Mbps for 1 Mbps to 100 Mbps (100BT) or to 10 Mbps
(10BT) (refer to Data Rate Limit Table). The rate limit is independently on the “receive side” and on the “transmit side”
on a per port basis. For 10BASE-T, a rate setting above 10 Mbps means the rate is not limited. On the receive side, the
data receive rate for each priority at each port can be limited by setting up Ingress Rate Control Registers. On the trans-
mit side, the data transmit rate for each priority queue at each port can be limited by setting up Egress Rate Control
Registers. The size of each frame has options to include minimum IFG (Inter Frame Gap) or Preamble byte, in addition
to the data field (from packet DA to FCS).
For ingress rate limiting, KSZ8873MLL/FLL/RLL provides options to selectively choose frames from all types, multicast,
broadcast, and flooded unicast frames. The KSZ8873MLL/FLL/RLL counts the data rate from those selected type of
frames. Packets are dropped at the ingress port when the data rate exceeds the specified rate limit.
For egress rate limiting, the Leaky Bucket algorithm is applied to each output priority queue for shaping output traffic.
Inter frame gap is stretched on a per frame base to generate smooth, non-burst egress traffic. The throughput of each
output priority queue is limited by the egress rate specified.