# Multicast

### 1. Summary

The Multicast page can be used to configure IGMP snooping and check the IGMP snooping operating status separately for each ProAV profile.
If multicasting via an AVoIP network, it is generally recommended that IGMP snooping be enabled, but that can lead to trouble if operated with improper settings.
By learning the basic principles of IGMP snooping, this page can be used for simple troubleshooting of IGMP snooping issues.

### 2. What’s IGMP snooping

IGMP snooping is a feature that prevents unnecessary multicast traffic from being forwarded.
Normally, multicast traffic is flooded to all affiliated ports in the same network, which wastes bandwidth by forwarding multicast traffic to ports where no multicast receiving terminal exists.
In contrast, if IGMP snooping is enabled, it saves bandwidth by only forwarding the necessary multicast traffic to ports with a receiving terminal connected.
The following example shows the difference between flooding and IGMP snooping, assuming receiving terminal A (RX A) only wants to receive Group A multicast traffic and receiving terminal B (RX B) only wants to receive Group B multicast traffic.
Flooding forwards both Group A and Group B traffic to the port where RX A is connected, but IGMP snooping only forwards Group A traffic to the port where RX A is connected.

In the case of flooding | In the case of IGMP snooping

Switches with IGMP snooping enabled use "IGMP Query" and "IGMP Report" to learn which multicast group traffic should be sent to which ports.
The following example shows the process flow of processing IGMP queries and IGMP reports.

1. One representative switch in the network periodically sends IGMP queries. The switch that sends the IGMP queries is called the "Querier".

2. When the multicast receiving terminal receives an IGMP query, it sends an IGMP report in response. The IGMP report contains information about the multicast group traffic that the receiving terminal wants to receive.

3. The switch learns which multicast group traffic to send to which port by snooping on the content in IGMP reports.

Since learned multicast group information is automatically deleted after a certain period of time, in order to maintain the correct learning state one querier must always be present in the same network.
If multiple queriers exist in the same network, only one querier is retained and the other switches automatically stop sending queries.
Note that even if there is no querier, the receiving terminal may spontaneously send an IGMP report, such as when the multicast receiving application is started in the receiving terminal.
Note that if multicast group information is learned without a querier present, the corresponding multicast group traffic might not be forwarded to ports where other receiving terminals are connected.

### 3. How to use this page

#### 3.1. Introduction

This page can be used as a troubleshooting tool if a problem related to IGMP snooping occurs.
IGMP snooping is enabled when profiles are specified on the ProAV profile page.

In this page, IGMP snooping settings can be changed and the IGMP snooping operating status checked separately for each ProAV profile.
First, select a profile from the profile select box in the upper left corner of the page.
If a ProAV profile has not been specified, specify the profile on the ProAV Profiles page.

#### 3.2. Warning message

When IGMP snooping is enabled, a warning message appears if the switch detects improper settings.
If a warning message appears, review the settings and change them if necessary.

- Warning message

  Display message | How to handle warnings
  The IGMP version (V2) specified in the profile does not match the version (V3) of the IGMP query received. Set the IGMP version in the profile to the same version as the IGMP query. | Change the IGMP version.
  Query transmission is stopped due to the presence of another querier | Enable IGMP query transmission.

#### 3.3. Change IGMP snooping settings

The following settings related to IGMP snooping can be changed for each ProAV profile

- IGMP snooping settings

  - Disabled ( Flood IP multicast packets )

    - Disable IGMP snooping
      Multicast packets are always forwarded to all ports in the same VLAN.

  - Enabled ( Control transmission of IP multicast packets )

    - Enable IGMP snooping.
      Multicast packets are forwarded only to the port to which the terminal you want to receive them is connected.
      This function monitors (snoops) IGMP messages exchanged between receiving terminals and a multicast router. It can suppress the flooding of multicast packets and reduce network bandwidth usage.

- Version

  - Select the IGMP version from the following items.

    - IGMPv3

    - IGMPv2

- IGMP query

  - No transmission
    IGMP query transmission function is disabled

  - Transmit periodically
    IGMP query transmission function is enabled. The transmission interval can be specified in the range of 20 seconds to 18000 seconds

- Processing method for unknown multicast frames

  - Specify the processing method for unknown multicast frames from below.

    - Flood

    - Discard

  - If IGMP snooping is disabled, "Flood" is automatically selected.

#### 3.4. Check IGMP snooping operating status

IGMP snooping learning status can be checked for each ProAV profile.

If a group is selected in the "Multicast Group" select box, the corresponding IGMP report/query learning status is displayed.
Mouse-over the port with the learning status displayed to show a tooltip with detailed IGMP report/query information.
Note that if both an IGMP report and IGMP query is received at the same port, information about both are displayed in the tooltip.

- IGMP report/query learning status

  Display item | Port display | Tooltip information
  --- | --- | ---
  IGMP report receiving port |  | Receiving port information Last received report information （ IP address, Version ）
  IGMP query receiving port |  | Receiving port information Received query information ( IP address, Version )

Since the learning status for multicast groups changes over time, click the "Update" button to update the display.

When a multicast group has been learned by an IGMP report, the IP address of the multicast group is displayed in the "Multicast Group" select box.
Traffic being sent to learned multicast groups is only forwarded to IGMP report receiving ports.

Unknown multicast groups are not displayed in the "Multicast Group" select box.
If a ProAV profile is specified, unknown multicast group traffic is discarded.
Please change the setting, if you want to flood an unknown multicast group.

If a problem that prevents receiving multicast traffic occurs, check whether the port indicator where the receiving terminal is connected is illuminated orange (which indicates it is an IGMP report receiving port).
If the connection port indicator is not orange, the receiving terminal might be connected to a port with a different profile. Check the profile setting for the port where it is connected.
If that does not solve the problem, try disabling IGMP snooping, but determine whether the bandwidth is sufficient before disabling IGMP snooping.

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