Querier Configuration

In an IGMP-enabled multicast network, devices can assume one of two roles within a network segment:

Querier:

• Responsible for sending Query messages
• Receives and processes Host Membership Reports (join messages) and Leave Group messages from hosts
• Maintains awareness of which multicast groups have active receivers (group members) on the segment connected to its interface
• Determines when group members leave by monitoring responses to its queries

Non-Querier:

• Passively receives Host Membership Reports from hosts
• Tracks which multicast groups have active receivers on its connected segment
• Relies on the Querier’s activity to determine when group members leave
• Does not initiate queries itself

Explanation of Principles

A network segment can have only one querier, so multicast devices must elect the querier through a selection process. The election rules are as follows:

After enabling the querier function, multicast Device A will default to being the querier for the current network segment during the IGMP protocol startup phase and begin sending query messages to the segment.If Device A receives a query message from multicast Device B with a smaller IP address than its own,Device A will switch from querier to non-querier status,Start the Other Querier Present Timer,Record Device B as the current querier for the segment.

When Device A is in non-querier status and receives query messages from querier Device B,It will update the Other Querier Present Timer.If the received query message comes from a new multicast Device C (not the previously recorded querier B) and C has a smaller IP address than B,Update the querier to Device C,Refresh the Other Querier Present Timer.

If Device A is in non-querier status and the Other Querier Present Timer expires:Device A will switch to querier status，Assume the responsibilities of the querier.

Querier Configuration

Operation	Command	Description
Enter the VLAN view	Vlan ID	-
Enable IGMP Snooping	igmp-snooping enable	-
Enable Querier Configuration	igmp-snooping querier enable	-

Configuration Example

The router connects to the user network through a Device. Key configurations and operational status are as follows:

Router Configuration:

IGMP querier functionality is enabled,Querier IP address has been modified

Network Components:

Two end-user devices: PC A and PC B,Intermediate Device running IGMP Snooping

Multicast Operations:

Multicast sources are transmitting data to groups 224.1.1.1 and 225.1.1.1

The router successfully:

Receives join messages from terminals,Receives leave messages from terminals,Multicast data from sources is properly forwarded to target PCs as designed.

Procedure

1. Create VLANs on the router and add interfaces connected to the Device

sonic(config)# vlan 100
sonic(config-vlan-100)# igmp snooping enable
sonic(config-vlan-100)# igmp-snooping querier enable
sonic(config)# interface ethernet 1
sonic(config-if-1)# switchport access vlan 100

Creating VLANs and Adding Member Interfaces

sonic(config)# vlan 100
sonic(config-vlan-100)# igmp snooping enable
sonic(config)# port-group ethernet 1-2
sonic(config-port-group-1-2)# switchport access vlan 100

Change Querier IP to 100.1.1.1

sonic(config)# vlan 100
sonic(config-vlan-100)# igmp-snooping querier-ip 100.1.1.1

Verify configuration

1. View multicast VLAN configuration

sonic(config)# do show l2-multicast-table
Total L2_multicast_forwarding_group counters: 4
(Source,Group)       Interface    Vlan     Uvlan    Mode
-------------------  -----------  -------  -------  ------
(0.0.0.0,225.1.1.1)  Ethernet2    Vlan100  Vlan100  INCL
                     Ethernet3    Vlan100  Vlan100  INCL
(0.0.0.0,224.1.1.1)  Ethernet2    Vlan100  Vlan100  INCL
                     Ethernet3    Vlan100  Vlan100  INCL

2. Check Querier Information and Change Source Address to 100.1.1.1