Datasheet

KSZ8895MQX/RQX/FQX/MLX
DS00002246A-page 40  2016 Microchip Technology Inc.
3.5.7 VLAN SUPPORT
The KSZ8895MQX/RQX/FQX/MLX supports 128 active VLANs and 4096 possible VIDs specified in IEEE 802.1q.
KSZ8895MQX/RQX/FQX/MLX 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. Ta ble 3 -9 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. Ta bl e 3-1 0 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.
Advanced VLAN features are also supported in KSZ8895MQX/RQX/FQX/MLX, such as “VLAN ingress filtering” and
“discard non PVID” defined in bits [6:5] of the port Register Control 2. These features can be controlled on a port basis.
3.5.8 RATE LIMITING SUPPORT
The KSZ8895MQX/RQX/FQX/MLX provides a fine resolution hardware rate limiting. The rate step is 64 kbps when the
rate limit is less than 1 Mbps rate for 100BT or 10BT. The rate step is 1 Mbps when the rate limit is more than 1 Mbps
rate for 100BT or 10BT (refer to Data Rate Selection Table which follow the end of the Port Register Queue 0-3 Ingress/
Egress Limit Control section). 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 transmit
side, the data transmit rate for each priority queue at each port can be limited by setting up Egress Rate Control Reg-
isters. 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).
3.5.8.1 Ingress Rate Limit
For ingress rate limiting, KSZ8895MQX/RQX/FQX/MLX provides options to selectively choose frames from all types,
multicast, broadcast, and flooded unicast frames by bits [3-2] of the port rate limit control register. The KSZ8895MQX/
RQX/FQX/MLX 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 or the flow control takes effect without packet dropped when the ingress
rate limit flow control is enabled by the port rate limit control register bit 4. The ingress rate limiting supports the port-
TABLE 3-9: FID+DA LOOK UP IN VLAN MODE
DA Found in
Static MAC Table
USE FID Flag? FID Match?
DA+FID Found in
Dynamic MAC Table
Action
No Do Not Care Do Not Care No
Broadcast to the membership ports
defined in the VLAN table bit [11:7].
No Do Not Care Do Not Care Yes
Send to the destination port defined
in the dynamic MAC table bit
[58:56].
Yes 0 Do Not Care Do Not Care
Send to the destination port(s)
defined in the static MAC table bit
[52:48].
Yes 1 No No
Broadcast to the membership ports
defined in the VLAN table bit [11:7].
Yes 1 No Yes
Send to the destination port defined
in the dynamic MAC table bit
[58:56].
Yes 1 Yes Do Not Ca re
Send to the destination port(s)
defined in the static MAC table bit
[52:48].
TABLE 3-10: FID+SA LOOK UP IN VLAN MODE
SA+FID Found in Dynamic MAC Table Action
No The SA+FID will be learned into the dynamic table.
Yes Time stamp will be updated.