Introduction to IGMP V1

IGMP: IGMP is internet group management protocol which is primarily used by multicast host to inform their local multicast router that when they wish to join specific multicast group and begin receiving group traffic.

There are various extension made in IGMP and there are three versions of IGMP currently used.

IGMP v1
IGMP v2
IGMP v3

Here we are going to discuss about IGMP v1 and in next section we will be discussing about other versions also.

IGMP v1:

IGMP is used to inform local router that a host is intended to receive the multicast traffic for particular group.

IGMP v1 Message Format:

Now here we are going to learn about working of IGMP v1.

Working of IGMP v1:

In working of IGMP v1 there are core concepts about following process.

IGMPv1 Query-Response Process
IGMPv1 Report Suppression method
IGMPv1 Querier Selection
IGMPv1 Join and Leave Process

IGMPv1 Query-Response Process

IGMP v1 uses Query-Response Model that helps multicast router to determine which multicast groups are active. Let’s understand this by below example:

Router 1 (the IGMP Querier) periodically sends an IGMPv1 Membership Query to the All-Hosts multicast group (224.0.0.1) on the local subnet. The default timer is (the default is every 60 seconds)
All hosts will receive this IGMPv1 Membership Query, and one host H1 who is member of multicast group 224.2.2.2 will responds first by multicasting an IGMPv1 Membership Report to All-Router ( 224.0.0.2 ) in the multicast group. By IGMPv1 Membership report it informs the routers on the subnet that a host is interested in receiving multicast traffic for group 224.2.2.2
As Host H2 is also listening to multicast group 224.2.2.2, and it will hear the IGMPv1 Membership Report that was multicast by Host H1. Host H1 will now suppresses the sending of its report for group 224.2.2.2.This Report Suppression mechanism helps reduce the amount of traffic on the local network.
Host H3 will also receive the IGMPv1 Membership Query, and it will responds by multicasting an IGMPv1 Membership Report to the multicast group 224.4.4.4. By this report routers will be aware that on the subnet a host is interested in receiving multicast traffic for group 224.4.4.4