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XG Series User's Guide Chapter 4 Switch Functions and their Configuration
IGMP Snooping
78
4.8.1 Registering Group Members
On receiving an IGMP Report message, the device registers a multicast MAC address to the IGMP snooping control table
for the port that received the IGMP Report message and the connecting multicast router port.
The following figure shows the relationship between the registered IP multicast address and the multicast MAC address.
MAC addresses that are registered with IGMP snooping are between 0100.5E00.0000 and 0100.5E7F.FFFF. An IP
multicast address is 32 bits. The first 4 bits are always 1110 followed by 28 bits that represent the IP multicast address
information. Of these 28 bits, the lower order 23 bits are mapped to a MAC address and the data in the higher order 5 bits
is not used.
Therefore 32 IP multicast addresses are mapped to the same single MAC address.
Note
• The device can register multicast groups up to a maximum value (Reference "1.2.3 System Maximum Values" (pg.34)).
Multicast packets that cannot be registered are those flooding all ports belonging to the same VLAN.
• If "igmpsnoop unknown flooding off" command is set, Multicast packets that cannot be registered are those not flooding all
ports belonging to the same VLAN (XG0224, XG0448).
XG
Registering Group Members
Multicast Router
Terminal 1
Port 1 Port 2 Port 3
VLAN 10
Port 8
IGMP Report
MAC : 0100.5E01.0203
Destination IP : 239.1.2.3
Group IP : 239.1.2.3
IGMP Report
MAC
Destination IP
Source IP
Group IP
Terminal 2
Terminal 3
: 0100.5E01.0203
: 239.1.2.3
: 192.168.10.20
: 239.1.2.3
1, 8
Port
0100.0501.0203
MAC Address Table
Port(MAC address)
(01:00:05:01:02:03)
IGMP snooping Control Table
VLAN(RouterPort)
VLAN
10 (8)
239.1.2.3
1
Reporter
192.168.10.20
Group IP
Multicast Address
0000001 00000011000000100010111100000000000000001 0000001 00000011000000100010111100000000000000001
1111 0000001 000000110000001001110 1111 0000001 000000110000001001110
0100.5E
01.02030100.5E
Lower 23 Bit Mapping
5 Bit Loss
Class D
Multicast MAC Address
1. 2. 3239. 1. 2. 3239.
Reserved for IPv4 Multicast
IP Multicast Address