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24-Port Gigabit (Hi-Power) PoE+ Ethernet Smart Managed Pro Switch with 2 SFP Ports
Configure Switching User Manual180
The following table describes the MFDB Statistics fields.
Table 35. MFDB Statistics information
Field Description
Max MFDB Table Entries The maximum number of entries that the Multicast Forwarding Database
table can hold (256 entries).
Most MFDB Entries Since Last
Reset
The largest number of entries that were present in the Multicast
Forwarding
Database table since last reset. This value is also known as th
e MFDB
high-water mark.
Current Entries The current number of entries in the Multicast Forwarding Database table.
Manage IGMP snooping
Internet Group Management Protocol (IGMP) snooping is a feature that allows a switch to
forward IPv4 multicast traffic intelligently. Multicast IPv4 traffic is traffic 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 can 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 destination address is received, the
switch forwards a copy to each of the remaining network segment
s 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 detected or
processed by all connected nodes. For multicast packets, this approach could lead to a less
ef
ficient use
of the network bandwidth, particularly when the packets are intended for a small
number of nodes only. Packets are flooded into network segments where no node is
receptive to the packet. Although nodes rarely incur any processing overhead to filter packets
addressed to unrequested group addresses, the nodes cannot transmit new packets onto the
shared media while the multicast packets are being flooded. Such as waste of bandwidth is
even worse when the LAN segment is not shared, for example in full-duplex links.
Allowing switches to snoop IGMP packets can solve this problem. While the IGMP packets
are
being forwarded
throughout the network, the switch uses the information in the packets to
determine which segments must receive packets that are directed to the group address.
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