Internet Group Management Protocal (IGMP)

Chapter 7 Internet Group Management Protocol (IGMP)

Topics Introduction to IP Multicast and IGMP  IP Multicasting Overview  Host Support  Sending IP Multicast Traffic  Receiving IP Multicast Traffic

 Router Support  The Multicast-Enabled IP Internetwork  The Internet’s Multicast-Enabled Backbone

Topics IGMP Message Structure  IGMP Version 1 (IGMPv1)  IGMP Version 2 (IGMPv2)  IGMP Version 3 (IGMPv3)

IGMP in Windows Server 2008 and Windows Vista  TCP/IP Protocol  Routing And Remote Access Service

Introduction to IP Multicast and IGMP IP Multicasting Overview ■ All multicast traffic is sent to a class D address in the range 224.0.0.0 through 239.255.255.255 (224.0.0.0/4). All traffic in the range 224.0.0.0 through 224.0.0.255 (224.0.0.0/24) is for the local subnet and is not forwarded by routers. Multicast-enabled routers forward multicast traffic in the range 224.0.1.0 through 239.255.255.255 with an appropriate Time to Live (TTL). ■ A specific multicast address is called a group address. ■ The set of hosts that listen for multicast traffic at a specific group address is called a multicast group or host group. Multicast group members can receive traffic to their unicast address and the group address. Multicast groups can be permanent or transient. A permanent group is assigned a well-known group address. An example of a permanent group is the allhosts multicast group, listening for traffic on the well-known multicast address of 224.0.0.1. The membership of a permanent group is transient; only the group address is permanent. ■ There are no limits on a multicast group’s size. ■ A host can send multicast traffic to the group address without belonging to the multicast group. ■ There are no limits to how many multicast groups to which a host can belong. ■ There are no limits on when members of a multicast group can join and leave a multicast group. ■ There are no limits on the location of multicast group members. IP multicast must be supported by the hosts and the routers of an IP internetwork

Introduction to IP Multicast and IGMP Host Support ■ Level 0 No support for sending or receiving IP multicast traffic ■ Level 1 Support for sending IP multicast traffic ■ Level 2 Support for sending and receiving IP multicast traffic You can also use the following registry value:

Introduction to IP Multicast and IGMP Sending IP Multicast Traffic Table 7-1 Recommended Values of the TTL for IP Multicast Traffic

Introduction to IP Multicast and IGMP Sending IP Multicast Traffic Table 7-1 Recommended Values of the TTL for IP Multicast Traffic

Receiving IP Multicast Traffic ■ Informs the Network Interface Layer technology to add the MAC-level multicast address that corresponds to the group address to the list of interesting destination MAC addresses.

■ If the group address is not in the range 224.0.0.1 through 224.0.0.255 (224.0.0.0/24), the IP module sends an IGMP Host Membership Report message to inform local routers to forward the host group traffic to the subnet of the listening host.

Introduction to IP Multicast and IGMP Router Support The Multicast-Enabled IP Internetwork

Figure 7-1 A multicast-enabled intranet showing multicast-enabled hosts and routers

Introduction to IP Multicast and IGMP Router Support The Internet’s Multicast-Enabled Backbone The portion of the Internet that is IP-multicast-enabled is known as the multicast backbone (MBONE). The MBONE was originally created to multicast the audio for Internet Engineering Task Force (IETF) meetings for members who could not attend. Today, the MBONE is used for the audio and video of IETF meetings, launches of the National Aeronautic and Space Administration (NASA) space shuttle, and teleconferences of all kinds. The MBONE is also the test bed for the development of IP multicast applications, tools, and routing protocols.

The MBONE is a logical IP multicast topology overlaid on the Internet’s physical unicast topology. Not all Internet service providers (ISPs) support the forwarding of IP multicast traffic. To connect two portions of the Internet that support IP multicast traffic, IP multicast traffic is tunneled or wrapped with another IP header addressed from one router to another router. The typical tunneling is called IP-in-IP tunneling and is described in RFC 1853. The MBONE is a series of multicast-enabled islands connected together with IP-in-IP tunnels.

IGMP Message Structure

Figure 7-2 IGMP message structure showing the IP header and Network Interface Layer header and trailer

IGMP Message Structure IGMP Version 1 (IGMPv1)  Host Membership Report  Host Membership Query  IGMPv1 Message Structure

Figure 7-3 The structure of an IGMPv1 message

IGMP Message Structure IGMP Version 2 (IGMPv2)    

The Leave Group Message The Group-Specific Query Message The Multicast Querier IGMPv2 Message Structure

IGMP Message Structure IGMPv2 Message Structure

Figure 7-4 The structure of an IGMPv2 message

IGMP Message Structure IGMP Version 3 (IGMPv3)  IGMPv3 Host Membership Query

Figure 7-5 The structure of the IGMPv3 Host Membership Query message

IGMP Message Structure IGMP Version 3 (IGMPv3)  IGMPv3 Host Membership Report

Figure 7-6 The structure of the IGMPv3 Host Membership Report message

IGMP Message Structure IGMP Version 3 (IGMPv3)  IGMPv3 Host Membership Report

Figure 7-7 The structure of the IGMPv3 Host Membership Report message group record

IGMP in Windows Server 2008 and Windows Vista

 TCP/IP Protocol  Routing And Remote Access Service  Interfaces in IGMP Router Mode  Interfaces in IGMP Proxy Mode

IGMP in Windows Server 2008 and Windows Vista

 Routing And Remote Access Service  Interfaces in IGMP Proxy Mode

Figure 7-8 The use of IGMP router mode and proxy mode

Summary IGMP provides a mechanism for hosts to register their interest in receiving IP multicast traffic sent to a specific group address (the Host Membership Report message), for hosts to indicate that they are no longer interested in receiving IP multicast traffic sent to a specific group address (the Leave Group message), and for routers to query the membership of all hostgroups (the General Host Membership Query) or a single host group (the Group-Specific Host Membership Query). TCP/IP for Windows Server 2008 and Windows Vista supports IGMPv1, IGMPv2, and IGMPv3, as well as IP multicast forwarding. In Windows Server 2008, the Routing and Remote Access service uses the IGMP routing protocol component and interfaces in IGMP router and proxy mode to maintain the IP multicast forwarding table and provide multicast forwarding in limited configurations.

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