Specifications
Micrel, Inc.
KSZ8895MQ/RQ/FMQ
VLAN Table
The VLAN table is used for VLAN table look-up. If 802.1q VLAN mode is enabled (Register 5 bit 7 = 1), this table is
used to retrieve VLAN information that is associated with the ingress packet. There are three fields for FID (filter ID),
Valid, and VLAN membership in the VLAN table. The three fields must be initialized before the table is used. There is
no VID field because 4096 VIDs are used as a dedicated memory address index into a 1024x52-bit memory space.
Each entry has four VLANs. Each VLAN has 13 bits. Four VLANs need 52 bits. There are a total of 1024 entries to
support a total of 4096 VLAN IDs by using dedicated memory address and data bits. Refer to Table 17 for details.
FID has 7-bits to support 128 active VLANs.
Address Name Description Mode
Initial Value
suggestion
Format of Static VLAN Table (Support Max 4096 VLAN ID entries and 128 Active VLANs)
12 Valid
1, the entry is valid.
0, entry is invalid.
R/W 0
11−7
Membership
Specifies which ports are members of the VLAN.
If a DA look-up fails (no match in both static and
dynamic tables), the packet associated with this VLAN
will be forwarded to ports specified in this field.
E.g., 11001 means Ports 5, 4, and 1 are in this VLAN.
R/W 11111
6−0
FID
Filter ID. KSZ8895MQ/RQ/FMQ supports 128 active
VLANs represented by these seven bit fields. FID is the
mapped ID. If 802.1q VLAN is enabled, the look-up will
be based on FID+DA and FID+SA.
R/W 0
Table 16. VLAN Table
If 802.1q VLAN mode is enabled, KSZ8895MQ/RQ/FMQ assigns a VID to every ingress packet when the packet is
untagged or tagged with a null VID, the packet is assigned with the default port VID of the ingress port. If the packet
is tagged with non-null VID, the VID in the tag is used. The look-up process starts from the VLAN table look-up based
on VID number with its dedicated memory address and data bits. If the entry is not valid in the VLAN table, the
packet is dropped and no address learning occurs. If the entry is valid, the FID is retrieved. The FID+DA and FID+SA
lookups in MAC tables are performed. The FID+DA look-up determines the forwarding ports. If FID+DA fails for look-
up in the MAC table, the packet is broadcast to all the members or specified members (excluding the ingress port)
based on the VLAN table. If FID+SA fails, the FID+SA is learned. To communicate between different active VLANs,
set the same FID; otherwise set a different FID.
The VLAN table configuration is organized as 1024 VLAN sets, each VLAN set consists of four VLAN entries, to
support up to 4096 VLAN entries. Each VLAN set has 52 bits and should be read or written at the same time
specified by the indirect address.
The VLAN entries in the VLAN set are mapped to indirect data registers as follow:
• Entry0[12:0] maps to the VLAN set bits[12-0] {register119[4:0], register120[7:0]}
• Entry1[12:0] maps to the VLAN set bits[25-13]{register117[1:0], register118[7:0], register119[7:5]}
• Entry2[12:0] maps to the VLAN set bits[38-26]{register116[6:0], register117[7:2]}
• Entry3[12:0] maps to the VLAN set bits[51-39]{register114[3:0], register115[7:0], register116[7]}
In order to read one VLAN entry, the VLAN set is read first and the specific VLAN entry information can be extracted.
To update any VLAN entry, the VLAN set is read first then only the desired VLAN entry is updated and the whole
VLAN set is written back. The FID in the VLAN table is 7-bit, so the VLAN table supports unique 128 flow VLAN
groups. Each VLAN set address is 10 bits long (Maximum is 1024) in the indirect address register 110 and 111, the
bit[9-8] of VLAN set address is at bit[1-0] of register 110, and the bit[7-0] of VLAN set address is at bit[7-0] of register
111. Each Write and Read can access up to four consecutive VLAN entries.
March 12, 2014
94
Revision 1.7