Advantech EKI-9228G-8CMI, User Manual

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EKI-9228G Series User Manual 176
4.4.8 IGMP Snooping
Internet Group Management Protocol (IGMP) Snooping is a feature that allows a
switch to forward multicast traffic intelligently on the switch. Multicast IP traffic is traf-
fic that is destined to a host group. Host groups are identified by class D IP
addresses, which range from 224.0.0.0 to 239.255.255.255. Based on the IGMP
query and report messages, the switch forwards traffic only to the ports that request
the multicast traffic. This prevents the switch from broadcasting the traffic to all ports
and possibly affecting network performance.
A traditional Ethernet network may be separated into different network segments to
prevent placing too many devices onto the same shared media. Bridges and
switches connect these segments. When a packet with a broadcast or multicast des-
tination address is received, the switch will forward a copy into each of the remaining
network segments in accordance with the IEEE MAC Bridge standard. Eventually,
the packet is made accessible to all nodes connected to the network.
This approach works well for broadcast packets that are intended to be seen or pro-
cessed by all connected nodes. In the case of multicast packets, however, this
approach could lead to less efficient use of network bandwidth, particularly when the
packet is intended for only a small number of nodes. Packets will be flooded into net-
work segments where no node has any interest in receiving the packet. While nodes
will rarely incur any processing overhead to filter packets addressed to un-requested
group addresses, they are unable to transmit new packets onto the shared media for
the period of time that the multicast packet is flooded. The problem of wasting band-
width is even worse when the LAN segment is not shared, for example in Full Duplex
links.
Allowing switches to snoop IGMP packets is a creative effort to solve this problem.
The switch uses the information in the IGMP packets as they are being forwarded
throughout the network to determine which segments should receive packets
directed to the group address.
4.4.8.1 Configuration
Use the IGMP Snooping Global Configuration and Status page to enable IGMP
snooping on the switch and view information about the current IGMP configuration.
To access this page, click Switching > IGMP Snooping > Configuration.
Figure 4.190 Switching > IGMP Snooping > Configuration
The following table describes the items in the previous figure.
Leave All Timer
(Centisecs) The amount of time to wait before sending a LeaveAll PDU after the
GARP application has been enabled on the interface or the last Lea-
veAll PDU was sent. A LeaveAll PDU indicates that all registrations will
shortly be deregistered. Participants will need to rejoin in order to
maintain registration.
Refresh Click Refresh to update the screen.
Edit Click Edit to edit the selected entries.
Item Description
Item Description
Admin Mode The administrative mode of IGMP snooping on the device.