Configuring Internet Group Management Protocol Snooping; Understanding Igmp Snooping - Juniper ACX1000 Configuration Manual

CHAPTER 15
Configuring Internet Group Management
Protocol Snooping

Understanding IGMP Snooping

Copyright © 2017, Juniper Networks, Inc.
Understanding IGMP Snooping on page 473
IGMP Snooping Interfaces and Forwarding on page 475
IGMP Snooping and Proxies on page 475
Multicast-Router Interfaces and IGMP Snooping Proxy Mode on page 476
Host-Side Interfaces and IGMP Snooping Proxy Mode on page 477
IGMP Snooping and Bridge Domains on page 477
Configuring IGMP Snooping on page 477
Configuring VLAN-Specific IGMP Snooping Parameters on page 478
Example: Configuring IGMP Snooping on page 479
Configuring IGMP Snooping Trace Operations on page 486
Snooping is a general way for Layer 2 devices, such as Juniper Networks MX Series Ethernet
Services Routers, to implement a series of procedures to "snoop" at the Layer 3 packet
content to determine which actions are to be taken to process or forward a frame. More
specific forms of snooping, such as Internet Group Membership Protocol (IGMP ) snooping
or Protocol Independent Multicast (PIM) snooping, are used with multicast.
Layer 2 devices (LAN switches or bridges) handle multicast packets and the frames that
contain them much in the same way the Layer 3 devices (routers) handle broadcasts.
So, a Layer 2 switch processes an arriving frame having a multicast destination media
access control (MAC) address by forwarding a copy of the packet (frame) onto each of
the other network interfaces of the switch that are in a forwarding state.
However, this approach (sending multicast frames everywhere the device can) is not the
most efficient use of network bandwidth, particularly for IPTV applications. IGMP snooping
functions by "snooping" at the IGMP packets received by the switch interfaces and building
a multicast database similar to that a multicast router builds in a Layer 3 network. Using
this database, the switch can forward multicast traffic only onto downstream interfaces
with interested receivers, and this technique allows more efficient use of network
bandwidth.
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