Netgear M6100 – Campus Edge and SMB Core Chassis Switches ソフトウェアガイド
Configure Switching Information
253
M6100, M5300, and M7100 Series Managed Switches
The following table describes the MFDB Statistics fields.
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 traffic that is destined
to a host group. Host groups are identified by class
forward multicast traffic intelligently on the switch. Multicast IP 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.
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 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.
segments. When a packet with a broadcast or multicast destination address is received, the
switch forwards 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 processed 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 are flooded into network segments where no node is
receptive to the packet. While nodes rarely incur any processing overhead to filter packets
addressed to unrequested group addresses, they cannot transmit new packets onto the
shared media for the period of time that the multicast packet is flooded. The problem of
wasting bandwidth is even worse when the LAN segment is not shared, for example in
full-duplex links.
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 are flooded into network segments where no node is
receptive to the packet. While nodes rarely incur any processing overhead to filter packets
addressed to unrequested group addresses, they cannot transmit new packets onto the
shared media for the period of time that the multicast packet is flooded. The problem of
wasting bandwidth 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 receive packets directed to the group address.
network to determine which segments receive packets directed to the group address.
Table 97. MFDB Statistics
Field
Description
Max MFDB Table Entries
The maximum number of entries that the Multicast Forwarding
Database table can hold.
Database table can hold.
Most MFDB Entries Since Last
Reset
Reset
The largest number of entries that were present in the Multicast
Forwarding Database table since last reset. This value is also known as
the MFDB high-water mark.
Forwarding Database table since last reset. This value is also known as
the MFDB high-water mark.
Current Entries
The current number of entries in the Multicast Forwarding Database
table.
table.