LAN9303 Datasheet, PDF (70/366 Pages) SMSC Corporation – Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII

Small Form Factor Three Port 10/100 Managed Ethernet Switch with Single MII/RMII/Turbo MII
Datasheet
6.4.2 Forwarding Rules
Upon ingress, packets are filtered or forwarded based on the following rules:
„ If the destination port equals the source port (local traffic), the packet is filtered.
„ If the source port is in the Disabled state, the packet is filtered.
„ If the source port is in the Learning or Listening / Blocking state, the packet is filtered (unless the
Spanning Tree Port State Override is in effect).
„ If the packet is a multicast packet and it is identified as a IGMP packet and IGMP monitoring is
enabled (respectively), the packet is redirected to the IGMP monitor port(s). This check is not done
on special tagged packets from the host CPU port when an ALR lookup is not requested. Refer to
Section 6.4.10.1, "Packets from the Host CPU," on page 80 for additional information.
„ If the destination port is in the disabled state, 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 in the Forwarding state.)
„ If the destination port is in the Learning or Listening / Blocking state, the packet is filtered (unless
the Spanning Tree Port State Override is in effect). (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 in the Forwarding state.)
„ If the Filter bit for the Destination Address is set in the ALR table, the packet is filtered.
„ If the packet has a unicast destination MAC address which is not found in the ALR table and the
Drop Unknown bit is set, the packet is filtered.
„ If the packet has a multicast destination MAC address which is not found in the ALR table and the
Filter Multicast bit is set, the packet is filtered.
„ If the packet has a broadcast destination MAC address and the Broadcast Storm Control level has
been reached, the packet is discarded.
„ If Drop on Yellow is set, the packet is colored Yellow, and randomly selected, it is discarded.
„ If Drop on Red 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.
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 bit 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 on Ingress is set, Admit Non Member is cleared, and the source
port is not a member of the incoming VLAN, the packet is filtered.
„ If Enable Membership Checking on Ingress 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 in the Forwarding state.)
„ If the destination address was not found in the ALR table (as 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.
Revision 1.3 (08-27-09)
70
DATASHEET
SMSC LAN9303/LAN9303i