S Layer 2 Managed Switch User Manual
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Network configuration allow us setting switch IGMP SNOOPING ,static state mutlicast,IP address parameter,aging time ,MAC
address binding configuration, At the same time , we can view switch present binding multicast address and port present
MAC binding address,switch present FDB table(ARL Table),ARP table in switch.
4.3.1 IGMP Snooping
Most switch deal with IP multicast as broadcast data.They transmit data to all switch port,not consider if this port need. IGMP
is IP group protocol that router and its mianboard exchanged information.
S support IGMP Snooping function. This
function can detect IGMP massage and get IP group information .
Switch will hold up IGMP router and the IGMP frame from
IGMP Host, parse and transmit it,setting the switch module rule of IGMP frame, made the IGMP frame from Router to the
port needed.
Switch is learning the IGMP frame between IGMP router and IGMP host, establish the IGMP table, control the package of this
IGMP group just transmit between the IGMP member ports, avoid the IGMP frame to broadcast in the switch, if the
application is VOD, and the data steam is very great, this function can reduce the loading of the switch and the data flow not
necessary.
Traditional switch IGMP monitoring network as following fig:
Multicast group attended:
Multicast server or multicast router send multicast IGMP query message at normal condition. Some is for general massage
searching, other is for particular message searching . Received this multicast searching message, switch sent this message
transmit to the same VLAN port, Mainboard of this port received searching message and have an interest in it ,it will reply a
IGMP report . after switch received this report ,a double layer multicast table established in this switch . As above fig showing ,
transferred multicast address is 224.1.2.3(01:00:5E:01:02:03),router searching port 1 connected multicast group and report
port 10 connected multicast mainboard will in VLAN 1 ,the table as follwing:
