IPv4 Multicast Protocols

In IP multicast transmission, the sender only needs to send data to a specified destination address and does not need to know the locations of receivers. It is the responsibility of network devices to forward data from the sender to the receivers. Multicast devices on the network must collect information about senders and duplicate and forward multicast data along the correct path. During multicast development, a complete suite of protocols are introduced.

Table 1 describes multicast protocols on an IPv4 network.

**Table 1** IPv4 multicast protocols
Protocol	Function	Remarks
Internet Group Management Protocol (IGMP)	IGMP manages IPv4 multicast group members and runs on the end of a multicast network (network segments where Layer 3 multicast devices connect to user hosts). Hosts use the IGMP protocol to join or leave multicast groups. Layer 3 multicast devices use the IGMP protocol to manage and maintain group memberships. IGMP can interact with upper-layer multicast routing protocols.	IGMP has three versions: IGMPv1, IGMPv2, and IGMPv3. All these versions support the any-source multicast (ASM) model. IGMPv3 can be independently used in the SSM model, whereas IGMPv1 and IGMPv2 use source-specific multicast (SSM) mapping.
Protocol Independent Multicast (PIM)	PIM runs on an IPv4 network and sends multicast data to multicast devices connected to group members interested in the data. PIM works in sparse mode (PIM-SM) or dense mode (PIM-DM). PIM-SM applies to large-scale networks with sparsely distributed group members, and PIM-DM applies to small-scale networks with densely distributed group members.	The PIM-DM model does not need to differentiate the ASM and SSM models. The PIM-SM model differentiates between ASM and SSM based on multicast addresses in data and protocol packets. If multicast addresses of packets are in the SSM group address range, PIM-SM uses the SSM model to provide multicast services. The PIM-SSM model is efficient and simplifies the multicast address allocation process. It is applicable when a group has only one specific source. If multicast addresses of packets are in the ASM group address range, PIM-SM uses the ASM model to provide multicast services.
Multicast Source Discovery Protocol (MSDP)	MSDP is an inter-domain multicast protocol that implements multicast forwarding between PIM-SM domains. Multicast devices in a PIM-SM domain use MSDP to discover multicast sources in other PIM-SM domains, and send information about active sources in other PIM-SM domains to receivers in the local PIM domain.	MSDP is required only when the ASM model is used.
Multiprotocol Border Gateway Protocol (MBGP)	MBGP enables multicast data to be transmitted between multicast sources and receivers in different autonomous systems (ASs).	-
IGMP snooping and IGMP snooping proxy	IGMP snooping enables a switch to create and maintain a Layer 2 multicast forwarding table by listening to IGMP packets exchanged between the upstream Layer 3 device and user hosts. The switch controls forwarding of multicast data packets based on the Layer 2 multicast forwarding table to reduce multicast data flooding on the Layer 2 network. IGMP snooping proxy enables the switch to act in place of an upstream device to send IGMP Query messages and receive IGMP Report/Leave messages from downstream devices. This function saves bandwidth between the upstream device and local switch.	IGMP snooping is an extension of IGMP on Layer 2 network devices. You can specify the IGMP snooping version on a switch to enable the switch to process IGMP packets of specific versions.