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An IGMP proxy device maintains a group membership database, which stores the group memberships
on all the downstream interfaces. Each entry comprises the multicast address, filter mode, and source list.
Such an entry is a collection of members in the same multicast group on each downstream interface.
An IGMP proxy device performs host functions on the upstream interface based on the database. It
responds to queries according to the information in the database or sends join/leave messages when the
database changes. On the other hand, the IGMP proxy device performs router functions on the
downstream interfaces by participating in the querier election, sending queries, and maintaining
memberships based on the reports.
IGMP support for VPNs
IGMP maintains group memberships on a per-interface base. After receiving an IGMP message on an
interface, IGMP processes the packet within the VPN to which the interface belongs. IGMP only
communicates with other multicast protocols within the same VPN instance.
Protocols and standards
• RFC 1112, Host Extensions for IP Multicasting
• RFC 2236, Internet Group Management Protocol, Version 2
• RFC 3376, Internet Group Management Protocol, Version 3
IGMP configuration task list
Task at a
lance
Configuring basic IGMP functions:
• (Required.) Enabling IGMP
• (Optional.) Specifying the IGMP version
• (Optional.) Configuring an interface as a static member interface
• (Optional.) Configuring a multicast group filter
Adjusting IGMP performance:
(Optional.) Configuring IGMP query parameters
(Optional.) Enabling IGMP fast-leave processing
(Optional.) Configuring IGMP SSM mappings
Configuring IGMP proxying:
• (Optional.) Enabling IGMP proxying
• (Optional.) Configuring multicast forwarding on a downstream interface
• (Optional.) Configuring multicast load splitting on the IGMP proxy
Configuring basic IGMP functions
Before you configure basic IGMP functions, complete the following tasks:
• Configure any unicast routing protocol so that all devices are interoperable at the network layer.
• Configure PIM.
• Determine the IGMP version.
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