Datasheet

 2017 Microchip Technology Inc. DS00002348A-page 27
KSZ8873MLL/FLL/RLL
3.4.2 IEEE 802.1Q VLAN SUPPORT
The KSZ8873MLL/FLL/RLL supports 16 active VLANs out of the 4096 possible VLANs specified in the IEEE 802.1Q
specification. KSZ8873MLL/FLL/RLL provides a 16-entries VLAN table that converts the 12-bits VLAN ID (VID) to the
4-bits Filter ID (FID) for address lookup. If a non-tagged or null-VID-tagged packet is received, the ingress port default
VID is used for lookup. In VLAN mode, the lookup process starts with VLAN table lookup to determine whether the VID
is valid. If the VID is not valid, the packet is dropped and its address is not learned. If the VID is valid, the FID is retrieved
for further lookup. The FID + Destination Address (FID+DA) are used to determine the destination port. The FID +
Source Address (FID+SA) are used for address learning.
Advanced VLAN features, such as “Ingress VLAN filtering” and “Discard Non PVID packets” are also supported by the
KSZ8873MLL/FLL/RLL. These features can be set on a per port basis, and are defined in registers 18, 34, and 50 for
ports 1, 2 and 3, respectively.
3.4.3 QOS PRIORITY SUPPORT
The KSZ8873MLL/FLL/RLL provides Quality of Service (QoS) for applications such as VoIP and video conferencing.
Offering four priority queues per port, the per-port transmit queue can be split into four priority queues: Queue 3 is the
highest priority queue and Queue 0 is the lowest priority queue. Bit [0] of registers 16, 32, and 48 is used to enable split
transmit queues for ports 1, 2, and 3, respectively. If a port's transmit queue is not split, high priority and low priority
packets have equal priority in the transmit queue.
There is an additional option to either always deliver high priority packets first or use weighted fair queuing for the four
priority queues. This global option is set and explained in bit [3] of register 5.
3.4.4 PORT-BASED PRIORITY
With port-based priority, each ingress port is individually classified as a high priority receiving port. All packets received
at the high priority receiving port are marked as high priority and are sent to the high-priority transmit queue if the cor-
responding transmit queue is split. Bits [4:3] of registers 16, 32, and 48 are used to enable port-based priority for ports
1, 2, and 3, respectively.
TABLE 3-10: FID+DA LOOKUP IN VLAN MODE
DA Found in
Static MAC
Table?
Use FID
Flag?
FID Match?
FID+DA Found in
Dynamic MAC
Table?
Action
No Don’t care Don’t care No
Broadcast to the membership ports
defined in the VLAN Table bits [18:16]
No Don’t care Don’t care Yes
Send to the destination port defined in
the Dynamic MAC Address Table bits
[53:52]
Yes 0 Don’t care Don’t care
Send to the destination port(s) defined
in the Static MAC Address Table bits
[50:48]
Yes 1 No No
Broadcast to the membership ports
defined in the VLAN Table bits [18:16]
Yes 1 No Yes
Send to the destination port defined in
the Dynamic MAC Address Table bits
[53:52]
Yes 1 Yes Do n’ t care
Send to the destination port(s) defined
in the Static MAC Address Table bits
[50:48]
TABLE 3-11: FID+SA LOOKUP IN VLAN MODE
FID+SA Found in Dynamic MAC Table? Action
No Learn and add FID+SA to the Dynamic MAC Address Table
Yes Update time stamp