VSC7440 datasheet(187/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

170

In addition to the PTP header modifications, address swapping and rewriting can also be enabled for

PTP frames. For PTP carried over UDP it can be useful to also swap MAC addresses, swap IP

addresses, change UDP port numbers, and preset the IPv4 TTL or IPv6 hop limit.

3.22

Analyzer Layer 2 Forwarding and Learning

The analyzer Layer 2 (ANA_L2) block performs the following tasks:

•

Determining forwarding decisions

•

Tracking network stations and their MAC addresses through learning and aging

•

Tracking and setting limits for number station learned per FID/ports

•

Scanning and updating the MAC table

The analyzer Layer 2 block makes a forwarding decision based on a destination lookup in the MAC table.

The lookup is based on the received Destination MAC address together with either the classified VID for

multicast traffic or the classified FID for unicast traffic. If an entry is found in the MAC table lookup, the

associated entry address is used for selecting forwarding port or ports. A flood forwarding decision is

made if no entry is found and forwarding to unknown destinations is permitted

(ANA_L3:VLAN:VLAN_CFG.VLAN_SEC_FWD_ENA).

The analyzer Layer 2 block performs a source lookup in the MAC table to determine if the source station

is known or unknown by looking at if there is an entry in the MAC table. If a MAC table entry exists, a port

move detection is performed by looking at whether the frame was received at the expected interface

specified. The source check can trigger the following associated actions.

•

Disabling forwarding from unknown or moved stations

•

Triggering automated learning

•

Sending copy to CPU

If the source station is known, the entry AGE_FLAG is cleared to indicate that source associated with the

entry is active. The AGE_FLAG is part of the aging functionality to remove inactive MAC table entries.

For more information, see Automated Aging (AUTOAGE), page 183.

The following subsections further describe the main analyzer Layer 2 blocks.

3.22.1

Analyzer MAC Table

The analyzer Layer 2 block contains a MAC table with 16,384 entries containing information about

stations learned or known by the device. The table is organized as a hash table with four buckets on each

row. Each row is indexed based on a hash value calculated based on the station’s (FID, MAC) pair.

The filtering ID (FID) used is either the FID from the VLAN table if a unicast MAC is looked up or else it is

the classified VID. It is possible to enforce use of FID for multicast (ANA_L3:COMMON:SERVICE_CFG).

MAC table organization is depicted in the following illustration.

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