Multicast
Multicast
1. Summary
The Multicast page can be used to configure IGMP snooping and checkthe IGMP snooping operating status separately for each ProAV profile.
If multicasting via an AVoIP network, it is generally recommended thatIGMP snooping be enabled, but that can lead to trouble if operated withimproper 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 samenetwork, which wastes bandwidth by forwarding multicast traffic to ports where no multicast receiving terminal exists.
In contrast, if IGMPsnooping is enabled, it saves bandwidth by only forwarding the necessary multicast traffic to ports with a receiving terminal connected.
Thefollowing example shows the difference between flooding and IGMPsnooping, assuming receiving terminal A (RX A) only wants to receiveGroup A multicast traffic and receiving terminal B (RX B) only wants toreceive Group B multicast traffic.
Flooding forwards both Group A and Group B traffic to the port where RX A is connected, but IGMP snoopingonly 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.
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One representative switch in the network periodically sends IGMP queries. The switch that sends the IGMP queries is called the "Querier".
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When the multicast receiving terminal receives an IGMP query, itsends an IGMP report in response. The IGMP report contains informationabout the multicast group traffic that the receiving terminal wants toreceive.
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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 deletedafter a certain period of time, in order to maintain the correctlearning state one querier must always be present in the same network.
If multiple queriers exist in the same network, only one querier isretained and the other switches automatically stop sending queries.
Note that even if there is no querier, the receiving terminal mayspontaneously send an IGMP report, such as when the multicast receivingapplication is started in the receiving terminal.
Note that ifmulticast group information is learned without a querier present, thecorresponding multicast group traffic might not be forwarded to portswhere 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 IGMPsnooping 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.
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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
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IGMP snooping settings
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Disabled ( Flood IP multicast packets )
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Disable IGMP snooping
Multicast packets are always forwarded to all ports in the same VLAN.
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Enabled ( Control transmission of IP multicast packets )
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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 receivingterminals and a multicast router. It can suppress the flooding ofmulticast packets and reduce network bandwidth usage.
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Version
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Select the IGMP version from the following items.
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IGMPv3
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IGMPv2
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IGMP query
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No transmission
IGMP query transmission function is disabled -
Transmit periodically
IGMP query transmission function isenabled. The transmission interval can be specified in the range of 20seconds to 18000 seconds
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Processing method for unknown multicast frames
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Specify the processing method for unknown multicast frames from below.
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Flood
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Discard
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If IGMP snooping is disabled, "Flood" is automatically selected.
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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 sameport, information about both are displayed in the tooltip.
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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 IPaddress 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, checkwhether the port indicator where the receiving terminal is connected isilluminated orange (which indicates it is an IGMP report receivingport).
If the connection port indicator is not orange, the receivingterminal might be connected to a port with a different profile. Checkthe profile setting for the port where it is connected.
If that doesnot solve the problem, try disabling IGMP snooping, but determinewhether the bandwidth is sufficient before disabling IGMP snooping.