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Product Overview

VMDS-10488 VSC7511 Datasheet Revision 4.2

2.3.2

Basic and Advanced Frame Classification

The basic and advanced frame classification in the ingress processing module receive all frames. The

basic and advanced classifiers determine a range of frame properties such as VLAN, Quality of Service

(QoS) class, and drop precedence level. This information is carried through the switch together with the

frame and affects policing, drop precedence marking, statistics collecting, security enforcement, Layer-2

forwarding, and rewriting.

The classification is a combination of a basic classification using configurable logic and more advanced

classification using a TCAM.

The classification engine understands up to two VLAN tags and can look for Layer-3 and Layer-4

information behind two VLAN tags. If frames are triple tagged, the higher-layer protocol information is not

extracted.

The following illustration shows the basic and advanced frame classification.

Figure 2 •

Basic and Advanced Frame Classification

The basic classification classifies each frame to a VLAN, a QoS class, a drop precedence (DP) level,

DSCP value, and an aggregation code. The basic classification also performs a general frame

acceptance check. The output from the basic classification may be overwritten or changed by the more

intelligent advanced classification using the IS1 TCAM.

Frame Acceptance The frame acceptance filter checks for valid combinations of VLAN tags against

the ingress port’s VLAN acceptance filter where it is possible to configure rules for accepting untagged,

priority-tagged, C-, and S-tagged frames. In addition, the filter also enables discarding of frames with

illegal MAC addresses (for instance null MAC address or multicast source MAC address).

VLAN Every incoming frame is classified to a VLAN by the basic VLAN classification. This is based on

the VLAN in the frame, or if the frame is untagged or the ingress port is VLAN unaware, it is based on the

ingress port’s default VLAN. A VLAN classification includes the whole TCI (PCP, DEI, and VID) and also

the TPID (C-tag or S-tag).

For double-tagged frames, it is selectable whether the inner or the outer tag is used.

The device can recognize S-tagged frames with the standard TPID (0x88A8) or S-tagged frames using a

custom programmable value. One custom value is supported by the device.

QoS, DP, and DSCP Each frame is classified to a Quality of Service (QoS) class and a drop

precedence level (frame color: green/yellow). The QoS class and DP level are used throughout the

device for providing queuing, scheduling, and congestion control guarantees to the frame according to

what is configured for that specific QoS class and color.

Basic Classification

Frame Data

Advanced Classification

IS1 First Lookup

Key:

- port mask

- inner and outer VLAN tags (VID, PCP, DEI, TPID)

- SMAC, DMAC

- SIP, DIP

- TCP/UDP ports

- frame type, DSCP, range checkers

IS1 Third Lookup

IS1 Second Lookup

IS1

QoS class

DP level

VLAN tag

header

Discard

Aggregation

code

VLAN pop count

Frame data

Classified VLAN

DP level

Classified DSCP

VLAN pop cnt

QoS, DP, and DSCP

PCP fromtag (inner or outer)

DSCP fromframe, trusted values only

Remap/rewrite of DSCP

Port default

VLAN

VLAN tag fromframe

Port VLAN

Frame Acceptance

Untagged, S-tagged, C-tagged

Special frames

Aggregation Code

L2-L4 frame data

DSCP value

QoS class

Customlookup

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