KSZ8895MQX Datasheet, PDF (39/108 Pages) Microchip Technology – Integrated 5-Port 10/100 Managed Ethernet Switch with MII/RMII Interface

KSZ8895MQX/RQX/FQX/MLX
TABLE 3-8: TAIL TAG RULES (CONTINUED)
Ingress to Port 5 (Host to KSZ8895MQX/RQX/FQX/MLX)
0,0,1,1
x,1,x,x
1,x,x,x
Queue 3 is used at destination port
Whatever send packets to specified port in bit [3:0]
Bit [6:0] will be ignored as normal (address look-up for destination)
Egress from Port 5 (KSZ8895MQX/RQX/FQX/MLX to Host)
Bit [1:0]
0,0
0,1
1,0
1,1
Source
Port 1 (packets from port 1)
Port 2 (packets from port 2)
Port 3 (packets from port 3)
Port 4 (packets from port 4)
3.5.5 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.
3.5.5.1 IGMP Snooping
The KSZ8895MQX/RQX/FQX/MLX 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.
3.5.5.2 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 broadcast 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 [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.
3.5.6 PORT MIRRORING SUPPORT
KSZ8895MQX/RQX/FQX/MLX 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 KSZ8895MQX/RQX/FQX/MLX will forward the packet to both Port 4 and Port
5. KSZ8895MQX/RQX/FQX/MLX 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 KSZ8895MQX/RQX/FQX/MLX will forward the packet to
both Ports 1 and 5.
• “Receive and Transmit” Mirror on a Port
- 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 pro-
grammed 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 KSZ8895MQX/RQX/FQX/MLX 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 KSZ8895MQX/RQX/FQX/MLX 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.
 2016 Microchip Technology Inc.
DS00002246A-page 39