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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

109

3.9.3

Forwarding Engine

The analyzer determines the set of ports to which each frame is forwarded, in several configurable steps.

The resulting destination port set can include any number of front ports, excluding the CPU port. The

CPU port is handled through te CPU extraction queue mask.

The analyzer request from the port modules is passed through all the processing steps of the forwarding

engine. As each step is carried out, the destination port set (DEST) and CPU extraction queue mask

(CPUQ) are built up.

In addition to the forwarding decision, the analyzer determines which frames are subject to learning (also

known as learn frames). Learn frames trigger insertion of a new entry in the MAC table or update of an

existing entry. Learning is presented as part of the forwarding, because in some cases, learning changes

the normal forwarding of a frame, such as secure learning.

During the processing, the analyzer determines a local frame property. The learning-disabled flag,

LRN_DIS is used in the SMAC Learning step:

•

If the learning-disabled flag is set, learning based on (SMAC, VID) is disabled.

•

If the learning-disabled flag is cleared, learning is conducted according to the configuration in the

SMAC learning step.

The following illustration shows the configuration steps in the analyzer.

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