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by the multicast switches, i.e., respond with membership report packets. The switches
send membership query packets in regular interval, and decide whether hosts of their
subnet join some group or not; on receiving quit group reports from the hosts, they send
query of associated group (IGMP v2) to determine whether there are members in a certain
group.
There are so far three versions of IGMP: IGMP v1 (define in RFC1112), IGMP v2 (defined
in RFC2236) and IGMP v3. Version 2 is the most widely used version at present.
Major improvements of IGMP v2 from v1 include:
1. Election mechanism for multicast switches in shared network segments.
A share network segment is a segment with several multicast switches. In this case, since
all switches running IGMP in the segment can receive membership report messages, only
one switch is needed to send membership query message. Therefore, there should be a
switch election mechanism to determine the switch acting as the querier. In IGMP v1, the
selection of querier is determined by multicast routing protocols; IGMP v2 improves this
feature and specifies the multicast switch of the lowest IP address to be the querier.
2. Quit group mechanism added in IGMP v2
In IGMP v1, the hosts quit the multicast without giving any message to any multicast
switch. And multicast switches have to decide the quit of multicast member by multicast
group response timeout. In version2, if a host decides to quit a multicast group, and it is
the host responding to the latest membership query message, it sends a quit-group
message.
3. Specific group query added in IGMP v2
In IGMP v1, the query of multicast switch aims for all multicast groups in that segment.
This query is called the universal group query. In IGMP v2, specific group query is
introduced in addition to the universal group query. The destination IP address of such
query packet is the IP address of the specified multicast group, the area part in the packet
of the group address is the IP address of the specified multicast group, too. Thus
response packets from the hosts of the other multicast groups can be avoided.
4. Maximum response time field added in IGMP v2
IGMP v2 has a field for maximum response time added,, so that hosts response time for
group query packets can be adjusted dynamically.
16.6.2 IGMP configuration
16.6.2.1 Configuration Task Sequence
1、 Enable IGMP (required)
Configure IGMP sub-parameters (optional)
(1) Configure IGMP group parameters.
a. Configuring IGMP group filtering criteria
b. Configure IGMP groups
c. Configure static IGMP groups