PIM-to-IGMP and PIM-to-MLD Message Translation Overview

This topic describes how the router translates Protocol Independent Multicast (PIM) join or prune messages into corresponding Internet Group Management Protocol (IGMP) or Multicast Listener Discovery (MLD) report or leave messages. It also explains how you can use this feature to forward multicast traffic across PIM domains in certain network topologies.

In some network configurations, customers are unable to run PIM between the customer edge–facing PIM domain and the core-facing PIM domain, although PIM is running in sparse mode within each of these domains. Because PIM is not running between the domains, customers with this configuration cannot use PIM to forward multicast traffic across the domains. Instead, they might want to use IGMP to forward IPv4 multicast traffic, or MLD to forward IPv6 multicast traffic across the domains.

To enable the use of IGMP or MLD to forward multicast traffic across the PIM domains in such topologies, you can configure the rendezvous point (RP) router that resides between the edge domain and core domain to translate PIM join or prune messages received from PIM neighbors on downstream interfaces into corresponding IGMP or MLD report or leave messages. The router then transmits the report or leave messages by proxying them to one or two upstream interfaces that you configure on the RP router. As a result, this feature is sometimes referred to as PIM-to-IGMP proxy or PIM-to-MLD proxy.

To configure the RP router to translate PIM join or prune messages into IGMP report or leave messages, include the pim-to-igmp-proxy statement at the [edit routing-options multicast] hierarchy level. Similarly, to configure the RP router to translate PIM join or prune messages into MLD report or leave messages, include the pim-to-mld-proxy statement at the [edit routing-options multicast] hierarchy level. As part of the configuration, you must specify the full name of at least one, but not more than two, upstream interfaces on which to enable the PIM-to-IGMP proxy or PIM-to-MLD proxy feature.

The following guidelines apply when you configure PIM-to-IGMP or PIM-to-MLD message translation:

• Make sure the router connecting the PIM edge domain and the PIM core domain is the static or elected RP router.
• Make sure the RP router is using the PIM sparse mode (PIM-SM) multicast routing protocol.
• When you configure an upstream interface, use the full logical interface specification (for example, ge-0/0/1.0) and not just the physical interface specification (ge-0/0/1).
• When you configure two upstream interfaces, the RP router transmits the same IGMP or MLD report messages and multicast traffic on both upstream interfaces. As a result, make sure that reverse-path forwarding (RPF) is running in the PIM-SM core domain to verify that multicast packets are received on the correct incoming interface and to avoid sending duplicate packets.
• The router transmits IGMP or MLD report messages on one or both upstream interfaces only for the first PIM join message that it receives among all of the downstream interfaces. Similarly, the router transmits IGMP or MLD leave messages on one or both upstream interfaces only if it receives a PIM prune message for the last downstream interface.
• Upstream interfaces support both local sources and remote sources.
• Multicast traffic received from an upstream interface is accepted as if it came from a host.

Related Topics

• Configuring PIM-to-IGMP Message Translation
• Configuring PIM-to-MLD Message Translation
• PIM Sparse Mode Overview