As we have learned in my previous blog about IGMP (Internet Group Management Protocol) version 1 and version2. Thisblog will cover IGMP version 3 how it is a better approach to use this version, and how IGMPv3 solves the Source authentic issue with the concept of Source-Specific Multicast (SSM).
Terminology of IGMP Version 3
IGMPv3 uses Membership Report message as it is like use as the previous IGMP version 1 & version 2.
IGMPv3 uses multicast address 224.0.0.22 on all enabledIGMPv3 multicast routers.
The main difference between IGMPv3 vs IGMPv1&2 is SSM (Source-specific Multicast). Only IGMPv3 supports the Source-specific Multicast feature. With the help of the SSM,the concept host has the option to get the multicast stream from a specific multicast server.
Report Message- A report message is sent by hosts which are wanting to join the multicast stream. This message is not all like the IGMP Version-1&2 it has some additional fields like multiple Group Records. Find the below-mentionedWireshark example for reference.
Frame 32: 60 bytes on wire (480 bits), 60 bytes captured (480 bits)
Ethernet II, Src: 02:02:31:04:00:00 (C2:02:31:04:00:10), Dst: IPv4mcast_00:00:16 (01:00:5e:10:00:16)
Internet Protocol Version 4, Src: 23.23.23.2 (23.23.23.2), Dst: 224.0.0.22 (224.0.0.22)
Internet Group Management Protocol
[IGMP Version: 3] Type: Membership Report (0x22)
Header checksum: Oxf5f9 [correct]
Num Group Records: 1
Group Record : 225.0.0.2 Allow New Sources
Record Type: Allow New Sources (5) Aux Data Len: 0 Num Src: 1 Multicast Address: 225.0.0.2 (225.0.0.2) Source Address: 2.2.2.2 (2.2.2.2)
Query Message-
Query Message used by the local router which has already enabled multicast router for the query they are using multicast IP address 224.0.0.1. And all client which wants to join the multicast traffic, are sending IGMPv3 Membership report message to multicast-enabled routers.
Leave Message- IGMPv3 also can leave the multicast group but like IGMPv2 there is no concept of Leave Group Message. IGMPv3 Membership Report message if they INCLUDE field is empty that means this Message is used leave the group.
IGMPv3 Header Information
Type– In the IGMPv3 Header Type field of message Members Query or report etc message information available.
MRT (Maximum Response Time)- As we learn in the last blog similarly, this field is used for the Maximum response time host to wait to send a report message for the same.
Checksum– It is 16-bits of checksum value.
Group Address- It is a Multicast Groups address that any host wants to join. It is 32 bits in length class D multicast address.
The number of Source addresses- This is the ‘n’ number of source addresses it is showing the information of how many total source addresses.
Source Address- This is the ipv4 IP address which indicates n number of 32 bits source addresses are there in this field.
In a summarized way, we can say that IGMP versions 1,2 & 3 all are used for sending and receiving the Multicast stream between servers to clients and clients to servers. With the help of some enhancement, that controls the multicast flooding and an Unknown source multicast issue.
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Author
Brijesh Yadav
Network Consultant Engineer
