3Com 400 Family, Руководство по настройке

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126 C
HAPTER
7: IGMP S
NOOPING
Configuring IGMP
Snooping
IGMP Snooping configuration includes:
■
Enabling/Disabling IGMP Snooping
■
Configuring Router Port Aging Time
■
Configuring Maximum Response Time
■
Configuring Aging Time of Multicast Group Member
Of the above configuration tasks, enabling IGMP Snooping is required, while
others are optional.
Enabling/Disabling IGMP
Snooping
Use the commands in Table 129 to enable/disable IGMP Snooping on Layer 2. First
enable IGMP Snooping globally in System View, and then enable IGMP Snooping
of the corresponding VLAN in VLAN View.
IGMP specific query message Transmitted from the multicast router to the multicast
members and used for querying if a specific group contains
any member. When received IGMP specific query message,
the switch only transmits the specific query message to the
IP multicast group which is queried.
IGMP report message Transmitted from the host to the multicast router and used
for applying to a multicast group or responding to the IGMP
query message. When received, the switch checks if the
MAC multicast group is ready to join. If the corresponding
MAC multicast group does not exist, the switch notifies the
router that a member is ready to join a multicast group,
creates a new MAC multicast group, adds the port that
received the message to the group, starts the port aging
timer, and then adds all the router ports in the native VLAN
of the port into the MAC multicast forwarding table.
Meanwhile, it creates an IP multicast group and adds the
port received to it. If the corresponding MAC multicast
group exists but does not contain the port that received the
report message, the switch adds the port into the multicast
group and starts the port aging timer. Then, the switch
checks if the corresponding IP multicast group exists. If it
does not exist, the switch creates a new IP multicast group
and adds the port that received the report message to it. If it
does exist, the switch adds the port. If the corresponding
MAC multicast group exists and contains the port, the
switch will only reset the aging timer of the port.
IGMP leave message Transmitted from the multicast group member to the
multicast router, to notify that a host has left the multicast
group. The Switch 4500 transmits the specific query
message, concerning the group, to the port that received
the message in an effort to check if the host still has other
members of this group, and then starts a maximum response
timer. If the switch has not received any report message
from the multicast group, the port will be removed from the
corresponding MAC multicast group. If the MAC multicast
group does not have any member, the switch will notify the
multicast router to remove it from the multicast tree.
Table 128 IGMP Snooping Terminology
Term Meaning