Internet Group Management Protocol

The Internet Accumulation Administration Agreement (IGMP) is a communications agreement acclimated by hosts and adjoining routers on IP networks to authorize multicast accumulation memberships.

IGMP is an basic allotment of the IP multicast specification. IGMP can be acclimated for online alive video and gaming, and allows added able use of assets if acknowledging these types of applications.

IGMP is acclimated on IPv4 networks. Multicast administration on IPv6 networks is handled by Multicast Listener Discovery (MLD) which uses ICMPv6 messaging in adverse to IGMP's bald IP encapsulation.

Architecture

A arrangement advised to bear a multicast account application IGMP ability use this basal architecture:

IGMP operates amid the applicant computer and a bounded multicast router. Switches featuring IGMP concern acquire advantageous advice by celebratory these IGMP transactions. Agreement Independent Multicast (PIM) is again acclimated amid the bounded and limited multicast routers, to absolute multicast cartage from the multicast server to abounding multicast clients.

IGMP operates aloft the arrangement layer, admitting it does not in fact act as a carriage protocol.1]not in commendation given]

Standards

There are three versions of IGMP, as authentic by Request for Comments (RFC) abstracts of the Internet Engineering Task Force (IETF). IGMPv1 is authentic by RFC 1112, IGMPv2 is authentic by RFC 2236 and IGMPv3 was initially authentic by RFC 3376 and has been adapted by RFC 4604 which defines both IGMPv3 and MLDv2. IGMPv2 improves over IGMPv1 by abacus the adeptness for a host to arresting admiration to leave a multicast group. IGMPv3 improves over IGMPv2 mainly by abacus the adeptness to accept to multicast basic from a set of antecedent IP addresses only.[2]

Host and router implementations

The IGMP agreement is implemented on a accurate host and aural a router. A host requests associates to a accumulation through its bounded router while a router listens for these requests and periodically sends out cable queries. The FreeBSD,note 1 Linuxnote 2 and Windows operating systems abutment IGMP at the host side.

For the server ancillary implementation, the Linux case uses a apparition such as mrouted to act as an IGMP Linux router. There are aswell absolute acquisition suites (such as XORP or Quagga), which about-face an accustomed computer into a full-fledged multicast router.

IGMPv3 packet structure

IGMP letters are agitated in bald IP packets with IP agreement amount 2.7 There is no carriage band acclimated with IGMP messaging, agnate to ICMP for example.

editMembership Query Message

Membership Queries are beatific by multicast routers to actuate which multicast addresses are of absorption to systems absorbed to its network. Routers periodically forward General Queries to brace the accumulation associates accompaniment for all systems on its network. Group-Specific Queries are acclimated for free the accession accompaniment for a accurate multicast address. Group-and-Source-Specific Queries acquiesce the router to actuate if any systems admiration accession of letters beatific to a multicast accumulation from a antecedent abode defined in a account of unicast addresses.

IGMPv3 packet structure

bit offset 0–3 4 5–7 8–15 16–31

0 Type = 0x11 Max Resp Code Checksum

32 Group Address

64 Resv S QRV QQIC Number of Sources (N)

96 Source Abode 1

128 Source Abode 2

. . .

Source Abode N

Max Resp Cipher

This acreage specifies the best time (in 1/10 second) accustomed afore sending a responding report. If the amount is beneath 128, the amount is acclimated directly. If the amount is 128 or more, it is interpreted as an backer and mantissa.

Checksum

This is the 16-bit one's accompaniment of the one's accompaniment sum of the absolute IGMP message.

Group Abode

This is the multicast abode getting queried if sending a Group-Specific or Group-and-Source-Specific Query. The acreage is zeroed if sending a General Query.

Resv

This acreage is reserved. It should be zeroed if beatific and abandoned if received.

S (Suppress Router-side Processing) Banderole

When this banderole is set, it indicates to accepting routers that they are to abolish the accustomed timer updates.

QRV (Querier's Robustness Variable)

If this is non-zero, it contains the Robustness Variable amount acclimated by the sender of the Query. Routers should amend their Robustness Variable to bout the a lot of afresh accustomed Query unless the amount is zero.

QQIC (Querier's Query Interval Code)

This cipher is acclimated for specify the Query Interval amount (in seconds) acclimated by the querier. If the amount is beneath 128, the amount is acclimated directly. If the amount is 128 or more, it is interpreted as an backer and mantissa.

Number of Sources (N)

This acreage specifies the amount of antecedent addresses present in the Query. For General and Group-Specific Queries, this amount is zero. For Group-and-Source-Specific Queries, this amount is non-zero, but bound by the network's MTU.

Source Abode i

The Antecedent Abode i fields are a agent of n IP unicast addresses, area n is the amount in the Amount of Sources (N) field.

IGMPv2 packet structure

Defined by RFC 2236

IGMPv2 packet structure

+ Bits 0–7 8–15 16–31

0 Type Max Resp Time Checksum

32 Group Address

Where:

Type is Membership Query (0x11), Membership Address (IGMPv1: 0x12, IGMPv2: 0x16), Leave Group (0x17) IGMPv3 adds blazon Membership Address (0x22)

Max Resp Time specifies the time absolute for the agnate report. The acreage has a resolution of 100 miliseconds, the amount is taken directly. This acreage is allusive alone in Membership Query (0x11); in added letters it is set to 0 and abandoned by the receiver.