D-Link DES-3326SR User Manual page 102

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
The IGMP Type codes are shown below:
Type Meaning
0x11
Membership Query (if Group Address is 0.0.0.0)
0x1 Specific Group Membership Query (if Group Address
1 is Present)
0x1 Membership Report (version 2)
6
0x1 Leave a Group (version 2)
7
0x1 Membership Report (version 1)
2
Table 5-14. IGMP Type Codes
Multicast routers use IGMP to manage multicast group
memberships:
•
An IGMP "report" is sent by a user's computer to join a
group
•
IGMP version 1 does not have an explicit 'leave'
message. Group members have an expiration timer,
and if this timer expires before a query response is
returned, the member is dropped from the group.
•
IGMP version 2 introduces an explicit "leave" report.
When a user wants to leave a group, this report is sent
to the multicast router (for IGMP version 2).
•
Multicast routers send IGMP queries (to the all-hosts
group address: 224.0.0.1) periodically to see whether
any group members exist on their subnetworks. If there
is no response from a particular group, the router
assumes that there are no group members on the
network, and multicast packets are not forwarded.
The TTL field of query messages is set to 1 so that the queries
do not get forwarded to other subnetworks.
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