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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

134

The rewriter performs five steps related to VLAN editing for each frame and destination:

VLAN popping - Zero, one, or two VLAN tags are popped from the frame.

ES0 lookup - ES0 is looked up for each of the frame’s destination ports. The action from ES0

controls the pushing of VLAN tags.

VLAN push decision - Deciding the number of new tags to push and which tag source to use for

each tag. Tag sources are: Port and ES0 (tag A and tag B).

Constructing the VLAN tags - The new VLAN tags are constructed based on the tag sources’

configuration.

VLAN pushing - the new VLAN tags are pushed.

3.13.1.1 VLAN Popping

The rewriter initially pops the number of VLAN tags specified by the VLAN_POP_CNT parameter

received with the frame from the classifier or VCAP IS1. Up to two VLAN tags can be popped. The

rewriter itself does not influence the number VLAN tags being popped.

3.13.1.2 ES0 Lookup

For each of the frame’s destination ports, VCAP ES0 is looked up using the ES0 key. See VCAP ES0,

page 92 for more information about ES0. The action from an ES0 hit is used in the following to determine

the frame’s VLAN editing.

3.13.1.3 VLAN Push Decision

After popping the VLAN tags, the rewriter decides whether to push zero, one, or two new VLAN tags to

the outgoing frame according to the port’s tagging configuration in register TAG_CFG and the action from

a potential VCAP ES0 hit. The up to two tags can originate from either the port (port tag) or ES0 (ES0 tag

A and ES0 tag B).

By default, the port can push one tag according to the port’s configuration in TAG_CFG. If the ES0 lookup

results in an entry being hit, the ES0 action can overrule the port configuration and push two tags by itself

(ES0 tag A and ES0 tag B) or it can combine port tagging and ES0 tagging.

The following illustration shows an overview of the available tagging options.

Figure 42 •

Tagging Overview

DMAC

SMAC

Outer tag

Inner tag

EtherType

Payload

(1) Port tag is controlled by REW:PORT:TAG_CFG.TAG_CFG.

Optional port tag(1)

ES0 tag A

No tag

Force port tag

No tag

ES0 tag B

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