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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

The VLAN classification determines a tag header for all frames. The tag header includes the following

information:

•

Priority Code Point (PCP)

•

Drop Eligible Indicator (DEI)

•

VLAN Identifier (VID)

•

Tag Protocol Identifier (TPID) type (TAG_TYPE). This field informs whether tag used for

classification was a C-tag or an S-tag.

The tag header determined by the classifier is carried with the frame through the switch and is used in

various places such as the analyzer for forwarding and the rewriter for egress tagging operations.

The device recognizes three kinds of tags based on the TPID, which is the EtherType in front of the tag:

•

Customer tags (C-TAGs), which use TPID 0x8100.

•

Service tags (S-TAGs), which use TPID 0x88A8 (IEEE 802.1ad).

•

Service tags (S-TAGs), which use a custom TPID programmed in SYS::VLAN_ETYPE_CFG.

For customer tags and service tags, both VLAN tags (tags with nonzero VID) and priority tags (tags with

VID = 0) are processed.

The tag header is either retrieved from a tag in the incoming frame or from a default port-based tag

header. The port-based tag header is configured in ANA:PORT:VLAN_CFG.

For double tagged frames, there is an option to use the inner tag instead of the outer tag

(VLAN_CFG.VLAN_INNNER_TAG_ENA).

In addition to the tag header, the port decides the number of VLAN tags to pop at egress

(VLAN_POP_CNT). If the configured number of tags to pop is greater than the actual number of tags in

the frame, the number is reduced to the number of actual tags in the frame.

The following illustration shows the flow chart for basic VLAN classification.

ANA:PORT:VLAN_CFG

Configures the port’s processing of VLAN information

in VLAN-tagged and priority-tagged frames.

Configures the port-based VLAN.

Per port

Table 29 •

VLAN Configuration Registers (continued)

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