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EX-series Switch - Multicast in a strictly Layer-2 Environment with IGMP Snooping enabled but without Multicast Router present.

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Article ID: KB12706 KB Last Updated: 05 Mar 2017Version: 2.0
Summary:
The EX-series Switch in a strictly layer-2 environment with multicast and IGMP snooping enabled, may require 'multicast-router' port to be configured depending on the topology. 

Symptoms:
With two EX-series Switches connnected via acces, or trunk (SW1----SW2), with one vlan and IGMP snooping enabled, it is possible that one of the receivers may not receive the membership report.



Solution:
EX Switches connected via access or trunk to each other with one vlan and IGMP snooping enabled.
                              
RCV1----[EX-SW1]---------[EX-SW2]-----RCV2
                 vlan10                 vlan10

In this configuration IGMP snooping on SW2 will "eat" the membership report sent by RCV2 for that group.  As a result, IGMP snooping on SW1 doesn't know that RCV2 on SW2 is also interested.

Solution:
The solution is to configure the port on SW1 or SW2 (the inter-switch connection port) as a multicast-router port.

Example:

set protocols igmp-snooping vlan all interface ge-0/0/0.0 multicast-router-interface

When SW1 port is configured as mrouter port, it sends the stream to SW2.  If SW2 port is configured as mrouter it sends the IGMP membership report sent from RCV2 over to SW2 and SW2 now knows that there is a listner downstream and marks that port as an interested listener.
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