VSC7440 datasheet(26/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

time stamping, and accounting. Although the VCAP IS2 is located in the ingress path of the device, it has

both ingress and egress capabilities.

The VCAP IS2 engine embeds powerful protocol awareness for well-known protocols such as LLC,

SNAP, ARP, IPv4, IPv6, and UDP/TCP. IPv6 is supported with full matching against both the source and

the destination IP addresses.

For each frame, up to two lookup keys are generated and matched against the VCAP entries.

3.2.4

Policing

Each frame is subject to one or more of the following policing operations.

•

Single-rate priority policers. Ingress port number and QoS class determine which policer to use.

•

Single-rate port policers. Ingress port number determines which policer to use.

•

VCAP single-rate policers. IS2 action selects which VCAP single-rate policer to use.

•

VCAP dual-rate policers. IS2 action selects which VCAP dual-rate policer to use.

•

Single-rate global storm policers. Frame characteristicS such as broadcast, unicast, multicast, or

learn frame select which policer to use.

•

Single-rate service broadcast, unicast, and multicast (BUM) policers for flooded frames. Service

classification and destination MAC address select which policer to use.

Each frame can trigger the following policers:

•

One BUM policer

•

One priority policer or one dual-rate VCAP policer

•

One port policer

•

One VCAP policer

•

Two port policers

•

Eight storm policers

Dual-rate policers are MEF-compliant, supporting both color-blind and color-aware operation. The initial

frame color is derived from the drop precedence level from the frame classification. The MEF coupling

mode is also configurable for each policer.

Dual-rate policers ensure Service Level Agreement (SLA) compliance. The outcome of this policing

operation is to mark each accepted frame as in-profile (green) or out-of-profile (yellow). Yellow frames

are treated as excess or discard-eligible and green frames are committed. Frames that exceed the

yellow/excess limits are discarded (red).

The two port policers and eight storm policers can be programmed to limit different types of traffic, such

as CPU-forwarded frames, learn frames, known or unknown unicast, multicast, or broadcast.

3.2.5

Layer 2 Forwarding

After the policers, the Layer 2 forwarding block of the analyzer handles all fundamental Layer 2

forwarding operations and maintains the associated MAC table, the VLAN table, and the aggregation

table. The device implements an 16K MAC table and a 4K VLAN table.

The main task of the analyzer is to determine the destination port set of each frame. The Layer 2

forwarding decision is based on various information such as the frame’s ingress port, source MAC

address, destination MAC address, and the VLAN identifier, as well as the frame’s VCAP actions,

mirroring, and the destination port’s link aggregation configuration.

Layer 2 forwarding of unicast and Layer 2 multicast frames is based on the destination MAC address and

the VLAN.

The switch can also L2-forward IPv4 and IPv6 multicast frames using additional Layer-3 information,

such as the source IP address. The latter enables source-specific IPv4 multicast forwarding (IGMPv3)

and source-specific IPv6 multicast forwarding (MLDv2). This process of L2-forwarding multicast frames

using Layer 3 information is called “snooping”, which is different from L3-forwarding (routing) of multicast

frames.

The following describes some of the contributions to the Layer 2 forwarding.

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