MDS212 Datasheet, PDF (61/111 Pages) Zarlink Semiconductor Inc – 12-Port 10/100Mbps Ethernet Switch

MDS212
Data Sheet
17.2.2 Blocking Multicast Packets Back To The Source Trunk
For local multicast packets, the Frame Engine needs to block the multicast packets from being sent to the same
Trunk Group as the receiving (source) port. To do it, the Search Engine utilizes the Trunk Group ID (TGID) in ECR1
Register.
The Frame Engine compares the TGID of the source and forwarding ports. If the two TGIDs are the same, the
Frame Engine blocks the forwarding port for this multicast packet. The Switch Engine provides the TGID of the
source port.
Example:
The following demonstrates the port trunking scheme for multicast packet forwarding.
4 Trunk Group in a switch:
Group 0: port 0,1,2 in device 0
Group 1: port 4, 5,6 in device 0
Group 2: port 1, 2,3 in device 1
Group 3: port 4, 5,6 in device 1
A multicast packet with VLAN INDEX=5 is received at port 0 of device 0.
The membership of this VLAN:
Device 0: port 0, 1, 2, 4, 5, 6, 7
Device 1: port 1, 2, 3, 4, 5, 6, 8
Hash Key = 3
Forwarding Port for each group with Hash Key=3,
Port 2 for Group 0
Port 4 for Group 1
Port 3 for Group 2
Port 6 for Group 3
Device 0
Local
Device 1
Remote
0 1 2 3 4 5 6 7 ....... 11
0 1 2 3 4 5 6 7 ....... 11
0
0
1
1
1
0
0
1
1
1
1
1
Forwarding Port Mask
for Key=3
100100111111
A
A
N
N
D
111011110000
VLAN Member
for INDEX=5
011111101000 ^D
001010010000
000010010000
Multicast packet received at port 0 of device 0
VLAN IDX=5, Hash Key=3
Forwarding ports
000100101000
Turn this port off
since port 2 has the
same TGID of source
port 0
Figure 23 - Multicast Packet Forwarding Example
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Zarlink Semiconductor Inc.