IGMP:

  •    The Internet Group Management Protocol. Some processes sometimes need to send the same message to a large number of receivers simultaneously. This is called multicasting, which is a one-to-many communication.
  •     For example, multiple stockbrokers can simultaneously be informed of changes in a stock price, or travel agents can be informed of a plane cancellation. Some other applications include distance learning and video-on-demand. Online Training, Video Conferencing etc.
  •      IGMP is not a multi casting routing protocol.  IGMP communication protocol is used by the nodes and adjacent routers on IP networks to interact and to establish group rules for multicast communication.
  •      It is a protocol that manages group membership. In any network, there are one or more multicast routers that distribute multicast packets to hosts or other routers. The IGMP protocol gives the multicast routers information about the membership status of hosts (routers) connected to the network.
  •       A multicast router may receive thousands of multicast packets every day for different groups. If a router has no knowledge about the membership status of the hosts, it must broadcast all these packets. This creates a lot of traffic and consumes bandwidth.
  •     A better solution is to keep a list of groups in the network for which there is at least one loyal member. IGMP helps the multicast router create and update this list.
IGMP Versions:
1. IGMP v1
2. IGMP v2 (default)
3. IGMP v3
IGMP Messages:



Message Format:
 Type: This 8-bit field defines the type of message.
  Maximum Response Time: This 8-bit field defines the amount of time in which a query must be answered. The value is                                                   in tenths of a second; for example, if the value is 100, it means 10 s.
 Checksum: This is a 16-bit field carrying the checksum. The checksum is calculated over the 8-byte message.
 Group address: The value of this field is 0 for a general query message. The value defines the group-id (multicast address of the group) in the special query, the membership report and the leave report messages.


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