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[EX] Verify Multicast client is listed in IGMP Snooping Database

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Article ID: KB21735 KB Last Updated: 06 May 2020Version: 3.0
Summary:

The primary objective of this article is to provide guidance with IGMP Snooping on EX Switch devices.

This article has a reference in the Resolution Guide to troubleshoot multicast issues on EX: KB21585-Resolution Guide - EX - Troubleshoot Multicast issue with EX device configured as Layer 2 switch

 

Symptoms:

The following topics are covered in this article:

  • Understanding and enabling IGMP snooping

  • Verifying that the client is listed in the IGMP Snooping Database

  • Disabling IGMP snooping

 

Solution:

Understanding and enabling IGMP Snooping

IGMP Snooping controls Multicast traffic in a switched network. The benefit with enabling igmp-snooping is that it conserves bandwidth on those segments of the network where no receiver has expressed interest in receiving packets sent for a multicast group.

IGMP Snooping on EX Series switches monitors the IGMP transmissions between a receiver and an IGMP-enabled Multicast router to keep track of the Multicast groups and associated member ports. The EX switch uses this information to make intelligent decisions and forward Multicast traffic to the intended destination interfaces only.

For more information on IGMP Snooping, refer to IGMP Snooping Overview

Note: igmp-snooping is enabled by default on EX switches.

To check if igmp-snooping is enabled, run the following configuration command:

show protocols 

The following output shows that igmp-snooping is enabled for all the VLANs of the EX device. However, it can also be enabled on a specific VLAN as well.

root@Juniper-EX# show protocols
igmp-snooping {
vlan all;

Enabling igmp-snooping on EX switch

[edit]
root@Juniper-EX#set protocols igmp-snooping vlan <VLAN NAME>

Verifying that the client is listed in the IGMP Snooping Database

For the topology used for explanation, refer to Sample Multicast Network Topology with Junos OS devices.

A series of commands exists to verify if a client is listed in the IGMP Snooping database.

  1. Run the following command:

show igmp-snooping membership detail

Check if the client interface is listed in the igmp-snooping database:

VLAN: default Tag: 0 (Index: 4)
VLAN: CLIENT Tag: 100(Index: 7)

Router interfaces: ge-0/0/15.0 dynamic Uptime: 00:34:46 timeout: 247

Group: 224.100.100.100 ge-0/0/10.0 timeout: 175 Last reporter: 192.168.100.10 Receiver count: 2,
Flags :< V2-hosts Static>

As seen above, we see that the client interface 192.168.100.10 has sent the IGMP report for the Multicast group 224.100.100.100 on the interface ge-0/0/10.0.

  1. Now run the following command:

show igmp-snooping route vlan <vlan-name>

In the output, note the Multicast group to which the VLAN has been added in the igmp-snooping database.

VLAN Group Next-hop
CLIENT 224.100.100.100, * 1321

In the above output, we see that the VLAN name is CLIENT, and the Group address is 224.100.100.100.

  1. Now run the following command:

show igmp-snooping vlans detail

VLAN: CLIENT, Tag: 100

Interface: ge-0/0/10.0, untagged, Groups: 1, Reporters: 1
Interface: ge-0/0/15.0, tagged, Groups: 0, Reporters: 0,

The above command confirms if the client is sending IGMP reports and if it is listed in the IGMP Snooping Database. The show igmp-snooping vlans detail command identifies the client interface, group address, and the VLAN that the group is part of.

If Reporters are seen showing 0 and Group 0, this concludes that the Multicast Clients are not sending reports.

Further, use monitor traffic interface ge-0/0/10 matching reports to confirm the same.

Disabling IGMP snooping

As mentioned above, igmp-snooping is enabled by default on EX switches. When would you disable igmp-snooping?

Refer to the following scenarios for examples of when IGMP Snooping is disabled:

 

Modification History:

2020-05-06: Updated links, changed/added reference articles for topology used; article is accurate and valid

 

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