1.0 Problem Statement

Network administrators may observe the following syslog message on a Cisco IOS-XE device, typically on a Switch Virtual Interface (SVI) or routed port:

%IGMP-3-QUERY_VERSION_CONFIGURED_DISCREPANCY: IGMP querier version (2) is lower than the configured version (3) on interface VlanXXX

This message indicates a functional conflict within the VLAN or Layer 2 segment. The local Cisco device is configured to operate using IGMP version 3, but it is detecting IGMP General Queries from a device operating as the IGMP querier using the older version 2 protocol. While IGMPv3 is backward-compatible, this discrepancy prevents the network segment from leveraging IGMPv3-specific features, such as Source-Specific Multicast (SSM) joins, and can lead to suboptimal multicast routing behavior.

The root cause is a mismatch in the IGMP version configuration between the designated IGMP querier for the segment and other multicast-aware devices, such as the switch generating the log.

2.0 Technical Analysis: The IGMP Querier Mechanism

The IGMP querier is a critical function in a multicast network. It is the network device responsible for periodically sending IGMP General Query messages onto a network segment to discover which multicast groups have interested members.

• Querier Election: On a multi-access segment with multiple multicast routers, a querier is elected. The election process defaults to the router with the lowest IP address on that segment. If Protocol Independent Multicast (PIM) is enabled, the PIM Designated Router (DR) typically assumes the role of the IGMP querier.
• Version Precedence: The version used by the active querier dictates the IGMP “mode” of the entire segment. Even if hosts and routers are IGMPv3-capable, if the querier sends v2 queries, all devices must operate in a v2-compatible mode to maintain interoperability.

The %IGMP-3-QUERY_VERSION_CONFIGURED_DISCREPANCY message is the system’s way of alerting the administrator that this forced downgrade in operational mode is occurring.

3.0 Diagnostic and Verification Procedure

To resolve this issue, the first step is to definitively identify the active IGMP querier on the affected VLAN.

1. Confirm Local Configuration: Verify the IGMP version explicitly configured on the affected interface of the local device.

   show running-config interface VlanXXX
   ! Look for the 'ip igmp version' command.
   

2. Identify the Active Querier: Use the following command to get detailed IGMP information for the interface. The output will clearly list the IP address of the device currently acting as the querier.

   show ip igmp interface VlanXXX
   

   • Sample Output Snippet:

     VlanXXX is up, line protocol is up
       Internet address is 192.168.10.1/24
       IGMP is enabled on interface
       Current IGMP host version is 3
       Current IGMP router version is 3
       IGMP query interval is 60 seconds
       IGMP querier timeout is 120 seconds
       IGMP max query response time is 10 seconds
       Last member query response interval is 1000 ms
       IGMP activity: 5 joins, 0 leaves
       Multicast routing is enabled on interface
       Multicast TTL threshold is 0
       IGMP querying enabled
       IGMP querier is 192.168.10.254  <-- This is the active querier
       Querier version is 2             <-- This is the detected version
     

   In this example, the device at 192.168.10.254 is the active querier and is operating in IGMPv2 mode.

3. Cross-reference with Layer 2 Snooping (Optional but Recommended): To further confirm from a Layer 2 perspective, use the snooping information.

   show ip igmp snooping querier vlan XXX
   

4.0 Remediation Strategies

Once the querier has been identified, proceed with one of the following remediation strategies.

Strategy 1: Align IGMP Versions (Recommended Best Practice)

The most robust and correct solution is to ensure a consistent IGMP version across all multicast routing devices in the segment.

1. Access the management interface of the identified querier device (e.g., 192.168.10.254 from the example).
2. Locate its IGMP configuration for the relevant interface or VLAN.
3. Modify its configuration to use IGMPv3. The exact command syntax will depend on the device vendor and platform (e.g., Cisco, FortiGate, Palo Alto).
4. This aligns the segment to the higher version, resolving the discrepancy and enabling full IGMPv3 functionality.

Strategy 2: Influence the Querier Election

If you intend for the local Cisco switch to be the querier, you must ensure it wins the election process.

1. Ensure the SVI on your Cisco switch has the lowest IP address among all other multicast routers on that VLAN.
2. Changing IP addresses can be service-impacting and should be done during a planned maintenance window.

Strategy 3: Conform to the Existing Querier (Workaround)

If the querier device cannot be modified (e.g., it is managed by another team or does not support IGMPv3), the only remaining option is to downgrade the IGMP configuration on the local Cisco device to match the querier.

1. Enter interface configuration mode for the affected SVI.

   configure terminal
   interface VlanXXX
   ip igmp version 2
   end
   

2. Note: This will resolve the syslog message but at the cost of losing IGMPv3 capabilities on this network segment. This should be considered a workaround, not a definitive solution.

5.0 Post-Remediation Verification

After applying a remediation strategy, re-run the verification command show ip igmp interface VlanXXX. Confirm that the “Querier version” now matches the configured IGMP version on your device. Finally, monitor system logs to ensure the %IGMP-3-QUERY_VERSION_CONFIGURED_DISCREPANCY message no longer appears.