MDS213 Datasheet, PDF (59/120 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps + 1Gbps Ethernet Switch

MDS213
Data Sheet
Whenever an IP Multicast data packet (destination MAC = 01-00-5e-xx-xx-xx, and destination IP address is within
the range of 224.0.1.0 and 239.255.255.255) is received, the Search Engine will use the MCT table to look up the
IP Multicast address of the incoming packet. Frame Engine then will use the result from the search (VLAN Index) to
forward this IP Multicast packet to its member ports according to the VLAN Port Mapping Table.
15.3.1 MCT Table
The MCT table is an internal table within the MDS213 chip that has a total of 2K entries. The CPU setups and read
the table one entry at a time through microcode in the HISC. There are two types of overlapped MCT entries, one
used for layer-2 MAC address based unicast switching, and the other for IP Multicasting.
15.3.1.1 MCT Structure For Unicast Frame
The MCT table is used by the Search Engine to forward unicast frames. By looking up a destination MAC address
from this table, the associated port number is found and used for packet forwarding decisions. The content of the
table is set up by the Search Engine at the reception of an incoming frame, if the Search Engine is not fully
occupied. When the Search Engine is too busy handling frame forwarding decisions, microcode in the HISC engine
will be assigned to do the learning job by setting up new MAC to Port associations.
An entry in this table can be setup by microcode in HISC through a CPU software command for static layer-2 packet
filtering based on either the source or destination address. An entry can be cleared by microcode in the HISC
through a CPU software command, during VLAN deletion, port link down, or when it is aged out. It will also be
cleared and a new one set up when a port change of a MAC address is detected.
Byte ^{3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 9 8 7 6 5 4 3 2 1 0}
1098765432109876543 210
0
MAC3
MAC2
MAC1
4
S
S D Port number
MAC5
P
MAC0 T
MAC4
8
Next Handle
12
T: Time stamp, used for aging. Set to 1 after MAC is found, and cleared to 0 when aged.
MAC[5:0]:MAC Address
S: Source MAC address filtering
D: Destination MAC address filtering
SP: Transmit Speed. 1- Gbps, 0-100Mbps
Next Handle: Pointer to the next entry in a hashed link list.
15.3.2 MCT structure for IP Multicast Packet
An IP Multicast entry in the MCT table can be setup or torn down by microcode in HISC through a CPU software
command for IP Multicasting. Whenever an IP multicast data packet is received, the Search Engine will use this
table to look up the IP Multicast address and VLAN ID of the incoming packet. If the IP Multicast address is found,
an internal VLAN Index from the MCT entry will be used by the Search Engine and Frame Engine to forward the IP
Multicast packet to the specific IP Multicast group members in a VLAN. If not, the packet will be forwarded to the
VLAN it belongs to.
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Zarlink Semiconductor Inc.