Specifications
Micrel, Inc.
KSZ8895MQ/RQ/FMQ
IGMP Support
There are two parts involved to support the Internet Group Management Protocol (IGMP) in Layer 2. The first part is
IGMP snooping, the second part is this IGMP packet to be sent back to the subscribed port. Describe them as
follows.
• IGMP Snooping
The KSZ8895MQ/RQ/FMQ traps IGMP packets and forwards them only to the processor (Port 5 SW5-MII/RMII).
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. Set register 5 bit [6] to ‘1’ to enable IGMP snooping.
• 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 port to downgrade
the performance.
Enable the tail tag mode, the host will know the IGMP packet received port from tail tag bits [1:0] and can send
back the response IGMP packet to this subscribed port by setting the bits [3:0] in the tail tag. Enable “Tail tag
mode” by setting Register 12 bit 1.
Port Mirroring Support
The KSZ8895MQ/RQ/FMQ supports “port mirror” comprehensively as:
• “Receive Only” mirror on a port
All the packets received on the port will be mirrored on the sniffer port. For example, Port 1 is programmed to be
“rx sniff,” and Port 5 is programmed to be the “sniffer port.” A packet, received on Port 1, is destined to Port 4
after the internal look-up. The KSZ8895MQ/RQ/FMQ will forward the packet to both Port 4 and Port 5.
KSZ8895MQ/RQ/FMQ can optionally forward even “bad” received packets to Port 5.
• “Transmit Only” mirror on a port
All the packets transmitted on the port will be mirrored on the sniffer port. For example, Port 1 is programmed to
be “tx sniff,” and Port 5 is programmed to be the “sniffer port.” A packet, received on any of the ports, is destined
to Port 1 after the internal look-up. The KSZ8895MQ/RQ/FMQ will forward the packet to both Ports 1 and 5.
• “Receive and Transmit” mirror on two ports.
All the packets received on port A AND transmitted on port B will be 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 “rx sniff,” Port 2 is programmed
to be “transmit sniff,” and Port 5 is programmed to be the “sniffer port.” A packet, received on Port 1, is destined
to Port 4 after the internal look-up. The KSZ8895MQ/RQ/FMQ will forward the packet to Port 4 only, since it does
not meet the “AND” condition. A packet, received on Port 1, is destined to Port 2 after the internal look-up. The
KSZ8895MQ/RQ/FMQ will forward the packet to both Port 2 and Port 5.
Multiple ports can be selected to be “rx sniffed” or “tx sniffed.” And any port can be selected to be the “sniffer port.”
All these per port features can be selected through Register 17.
VLAN Support
The KSZ8895MQ/RQ/FMQ supports 128 active VLANs and 4096 possible VIDs specified in IEEE 802.1q.
KSZ8895MQ/RQ/FMQ provides a 128-entry VLAN table, which correspond to 4096 possible VIDs and converts to
FID (7 bits) for address look-up max 128 active VLANs. If a non-tagged or null-VID-tagged packet is received, then
the ingress port VID is used for look-up when 802.1q is enabled by the global register 5 control 3 bit 7. In the VLAN
mode, the look-up process starts from VLAN table look-up to determine whether the VID is valid. If the VID is not
valid, the packet will then be dropped and its address will not be learned. If the VID is valid, FID is retrieved for
further look-up by the static MAC table or dynamic MAC table. FID+DA is used to determine the destination port. The
following table describes the different actions in different situations of DA and FID+DA in the static MAC table and
dynamic MAC table after the VLAN table finish a look-up action. FID+SA is used for learning purposes. The following
table also describes learning in the dynamic MAC table when the VLAN table has done a look-up in the static MAC
table without a valid entry.
March 12, 2014
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Revision 1.7