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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

105

In order for a frame to be routed, the frame’s VLAN tags must all be valid, and routing must be enabled

for the number of VLAN tags in the frame.

The settings in BASIC_TPID_AWARE_DIS define each of three processed VLAN tags of which TPID

values are valid for routing. The settings in RT_TAG_CTRL define the number of valid VLAN tags that

must be present in routable frames.

Example: If routing is enabled for single-tagged frames with TPID=0x8100, configure the following:

•

BASIC_TPID_AWARE_DIS = 0x7FFE. This invalidates all TPIDs except TPID = 0x8100 for outer

most VLAN tag.

•

RT_TAG_CTRL = 0x2. This enables routing of frames with one accepted tag only.

In this example, if an untagged frame is received, it is not routable because routing is not enabled for

untagged frames. If a single-tagged frame is received with for instance TPID=0x88A8 or a double-tagged

frame is received with for instance TPID=0x8100 for outer tag and TPID=0x8100 for inner tag, they are

not routable because not all their VLAN tags are valid.

Example: To configure routing on a VLAN unaware port where routing is enabled for untagged frames

only, set RT_TAG_CTRL = 0x1 to enable routing of untagged frames only.

3.16.1.4 Frame Acceptance Filtering

The following table lists the registers associated with frame acceptance filtering.

Based on the configurations in the FILTER_CTRL register, the classifier can discard certain frame types

that are normally not allowed to enter the network, such as the following.

•

Frames with a multicast source MAC address (bit 40 in address is set)

•

Frames with a null source or null destination MAC address (address = 0x000000000000)

The VLAN acceptance filter decides whether a frame’s VLAN tagging is allowed on the port. It has three

stages where each stage checks one of the up to three processed VLAN tags. Each stage is

programmable independently of the other stages in ANA_CL:PORT:VLAN_FILTER_CTRL. The following

illustration shows the flowchart for the VLAN acceptance filter.

Table 68 •

Frame Acceptance Filtering Registers

Description

Replication

ANA_CL::FILTER_CTRL

Configures filtering of special frames

Per port

ANA_CL::VLAN_FILTER_CTRL

Configures VLAN acceptance filter

Three per port

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