D-Link DES-3326 User Manual - page 114
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
100
Switch Management and Operating Concepts
Type Meaning
0X11 Membership Query (if Group Address is 0.0.0.0)
0x11
Specific Group Membership Query (if Group Address is
Present)
0x16
Membership Report (version 2)
0x17
Leave a Group (version 2)
0x12
Membership Report (version 1)
Table 5-11. 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.
IGMP version 2 introduces a few extensions to IGMP version 1
such as, the election of a single multicast querier for each network,
explicit ‘leave’ reports, and queries that are specific to a particular
multicast group.