Internet Group Management Protocol (Igmp) - D-Link DES-3326SR Manual

Internet Group Management Protocol (IGMP)

End users that want to receive multicast packets must be able to inform nearby routers that they want to become a multicast
group member of the group these packets are being sent to.
multicast routers to maintain multicast group membership. IGMP is also used to coordinate between multiple multicast
routers that may be present on a network by electing one of the multicast routers as the 'querier'. This router then keep track
of the membership of multicast groups that have active members on the network. IGMP is used to determine whether the
router should forward multicast packets it receives to the subnetworks it is attached to or not. A multicast router that has
received a multicast packet will check to determine if there is at least one member of a multicast group that has requested to
receive multicast packets from this source. If there is one member, the packet is forwarded. If there are no members, the
packet is dropped.
IGMP Versions 1 and 2
Users that want to receive multicast packets need to be able to join and leave multicast groups. This is accomplished using
IGMP.
The IGMP Type codes are shown below:
IGMP Type Codes
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)
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.
D-Link DES-3326SR Layer 3 Switch
The Internet Group Management Protocol (IGMP) is used by
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