LAN9353 Datasheet, PDF (210/523 Pages) Microchip Technology – Interfaces at up to 200Mbps via Turbo MII

LAN9353
• If the packet has a broadcast destination MAC address and the Broadcast Storm Control level has been reached,
the packet is discarded.
• If the Drop on Yellow field in the Buffer Manager Configuration Register (BM_CFG) is set, the packet is colored
Yellow and randomly selected, it is discarded.
• If the Drop on Red field in the Buffer Manager Configuration Register (BM_CFG) is set and the packet is colored
Red, it is discarded.
• If the destination address was not found in the ALR table (an unknown or a broadcast) and the Broadcast Buffer
Level is exceeded, the packet is discarded.
• If there is insufficient buffer space, the packet is discarded.
• If the destination address was not found in the ALR table (an unknown or a broadcast) or the destination address
was found in the ALR table with the ALR result indicating multiple destination ports and the port forward states
resulted in zero valid destination ports, the packet is filtered.
• For cases where the packet is not filtered, the ALR Override Enable bit in the Switch Engine ALR Override Regis-
ter (SWE_ALR_OVERRIDE) is checked for the source port and, if set, the packet is redirected to the specified
override destination.
When the switch is enabled for VLAN support, these following rules also apply:
• If the packet is untagged or priority tagged and the Admit Only VLAN field in the Switch Engine Admit Only VLAN
Register (SWE_ADMT_ONLY_VLAN) for the ingress port is set, the packet is filtered.
• If the packet is tagged and has a VID equal to FFFh, it is filtered.
• If Enable Membership Checking field in the Switch Engine Port Ingress Configuration Register (SWE_PORT_IN-
GRSS_CFG) is set, Admit Non Member field in the Switch Engine Admit Non Member Register (SWE_AD-
MT_N_MEMBER) is cleared and the source port is not a member of the incoming VLAN, the packet is filtered.
• If Enable Membership Checking field is set and the destination port is not a member of the incoming VLAN, the
packet is filtered. (This rule is for a destination MAC address which is found in the ALR table and the ALR result
indicates a single destination port. When there are multiple destination ports or when the MAC address is not
found, the packet is sent to only those ports that are members of the VLAN. This rule is also suppressed if ALR
Result Override is enabled.)
• If the destination address was not found in the ALR table (an unknown or broadcast) or the destination address
was found in the ALR table with the ALR result indicating multiple destination ports and the VLAN broadcast
domain containment resulted in zero valid destination ports, the packet is filtered.
• For the last three cases, if the VID is not in the VLAN table, the VLAN is considered foreign and the membership
result is NULL. A NULL membership will result in the packet being filtered if Enable Membership Checking is set.
A NULL membership will also result in the packet being filtered if the destination address is not found in the ALR
table (since the packet would have no destinations).
10.3.3 TRANSMIT PRIORITY QUEUE SELECTION
The transmit priority queue may be selected from five options. As shown in Figure 10-2, the priority may be based on:
• The static value for the destination address in the ALR table
• The precedence bits in the IPv4 TOS octet
• The DIFFSERV mapping table indexed by the IPv4 TOS octet or the IPv6 Traffic Class octet
• The VLAN tag priority field using the per port Priority Regeneration table
• The port default with separate values for packets with or without a broadcast destination address.
DS00001925A-page 210
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