TCP/IP Tutorial and Technical Overview - IBM Redbooks

To join a group, the host sends an IGMP membership report packet through an
attached interface. The report is addressed to the desired multicast group. A host
does not need to join the all hosts group (224.0.0.1). Membership in this group is
automatic.
IGMPv3 specific host operations
In IGMPv3, hosts specify a list of multicast addresses from which they want to
receive messages, or a list of multicast addresses from which they do not want to
receive messages. Hosts can then later alter these lists to add or remove
multicast addresses. This can be achieved using the filter-mode-change and
source-list-change records.
Note: If no interface state exists, it is created using the filter-mode-change
record.
The use of these records is demonstrated using Table 6-1. In this example, the
current state indicates what subsets of multicast addresses (A and B) are
currently included or excluded. The desired state indicates the subsets desired to
be included or excluded. The Records needed to achieve desired state show the
records which can must be sent to achieve this change. Note that the group type
records are abbreviated as follows:
► CHANGE_TO_INCLUDE_MODE: To_in
► CHANGE_TO_EXCLUDE_MODE: To_ex
► ALLOW_NEW_SOURCES: Allow
► BLOCK_OLD_SOURCES: Block
Table 6-1 IGMPv3 list changes using group record types
Current state Desired state Records needed to achieve desired state
1 Include () Include (A) To_in (A)
2 Include (A) Include (B) Allow (B-A), Block (A-B)
3 Include (B) Exclude (A) To_ex (A)
4 Exclude (A) Exclude (B) Allow (A-B), Block (B-A)
5 Exclude (B) Include (A) To_in (A)
These steps are summarized as follows:
1. No source address lists currently exists. The subset of lists A is added by
issuing a CHANGE_TO_INCLUDE_MODE specifying the A subset.
248 TCP/IP Tutorial and Technical Overview