Template:Short description Template:IPstack
The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast and allows the network to direct multicast transmissions only to hosts that have requested them.
IGMP can be used for one-to-many networking applications such as online streaming video and gaming, and allows more efficient use of resources when supporting these types of applications.
IGMP is used on IPv4 networks. Multicast management on IPv6 networks is handled by Multicast Listener Discovery (MLD) which is a part of ICMPv6 in contrast to IGMP's bare IP encapsulation.
ArchitectureEdit
A network designed to deliver a multicast service using IGMP might use this basic architecture:
File:IGMP basic architecture.png
IGMP operates between a host and a local multicast router. Switches featuring IGMP snooping also derive useful information by observing these IGMP transactions. Protocol Independent Multicast (PIM) is then used between the local and remote multicast routers to direct multicast traffic from hosts sending multicasts to hosts that have registered through IGMP to receive them.
IGMP operates on the network layer (layer 3), just the same as other network management protocols like ICMP.<ref name="Forouzan 2012">Template:Cite book</ref>
The IGMP protocol is implemented on hosts and within routers. A host requests membership to a group through its local router while a router listens for these requests and periodically sends out subscription queries. A single router per subnet is elected to perform this querying function. Some multilayer switches include an IGMP querier capability to allow their IGMP snooping features to work in the absence of an IGMP-capable router in the layer 2 network.
IGMP is vulnerable to some attacks,<ref>Spoofed IGMP report denial of service vulnerability.</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>IGMP Security Problem Statement and Requirements Template:Webarchive.</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and firewalls commonly allow the user to disable it if not needed.
VersionsEdit
There are three versions of IGMP.<ref name="Cisco Multicast">Template:Citation</ref> IGMPv1 was defined in 1989.Template:Ref RFC IGMPv2, defined in 1997,Template:Ref RFC improves IGMPv1 by adding the ability for a host to signal a desire to leave a multicast group.
In 2002, IGMPv3 improved IGMPv2 by supporting source-specific multicast<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and introduces membership report aggregation.Template:Ref RFC The support for source-specific multicast was improved in 2006.Template:Ref RFC
The three versions of IGMP are backward compatible. A router supporting IGMPv3 can support clients running IGMPv1, IGMPv2, and IGMPv3. IGMPv1 uses a query-response model. Queries are sent to Template:IPaddr. Membership reports are sent to the group's multicast address. IGMPv2 accelerates the process of leaving a group and adjusts other timeouts. Leave-group messages are sent to Template:IPaddr. A group-specific query is introduced. Group-specific queries are sent to the group's multicast address. A means for routers to select an IGMP querier for the network is introduced. IGMPv3 introduces source-specific multicast capability. Membership reports are sent to Template:IPaddr.
MessagesEdit
There are several types of IGMP messages:
- General membership queries
- Sent by multicast routers to determine which multicast addresses are of interest to systems attached to the network(s) they serve to refresh the group membership state for all systems on its network.
- Group-specific membership queries
- Used for determining the reception state for a particular multicast address.
- Group-and-source-specific queries
- Allow the router to determine if any systems desire reception of messages sent to a multicast group from a source address specified in a list of unicast addresses.
- Membership reports
- Sent by multicast receivers in response to a membership query or asynchronously when first registering for a multicast group.
- Leave group messages
- Sent by multicast receivers when specified multicast transmissions are no longer needed at the receiver.
IGMP messages are carried in bare IP packets with IP protocol number 2.Template:Ref RFC Similar to the Internet Control Message Protocol, there is no transport layer used with IGMP messaging.
IGMPv2 messagesEdit
Template:APHD Template:APHD Template:APHD Template:APHD
Message Type value Membership Query Template:Mono IGMPv1 Membership Report Template:Mono IGMPv2 Membership Report Template:Mono IGMPv3 Membership Report Template:Mono Leave Group Template:Mono
- Template:APHD
- Template:APHD
- Template:APHD
- The message is sent to the following IP multicast addresses:Template:Ref RFC
Message type Multicast address General Query All hosts (Template:IPaddr) Group-Specific Query The group being queried Membership Report (all IGMP versions) The group being reported Leave Group All routers (Template:IPaddr)
IGMPv3 membership queryEdit
Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
ImplementationsEdit
FreeBSD,<ref group=note>IGMPv3 was added to FreeBSD in version 8.0.</ref> Linux<ref group=note>IGMPv3 was added in the Linux 2.5 kernel series.</ref> and Windows all support IGMP on the host side.