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Multicast Protocols User Guide
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Verifying MLD Snooping on Switches

date_range 23-Nov-23
Note:

This topic uses Junos OS with support for the Enhanced Layer 2 Software (ELS) configuration style. If your switch runs software that does not support ELS, see Verifying MLD Snooping on EX Series Switches (CLI Procedure). For ELS details, see Using the Enhanced Layer 2 Software CLI.

Multicast Listener Discovery (MLD) snooping constrains the flooding of IPv6 multicast traffic on VLANs. This topic describes how to verify MLD snooping operation on a VLAN.

Verifying MLD Snooping Memberships

Purpose

Verify that MLD snooping is enabled on a VLAN and determine group memberships.

Action

Enter the following command:

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user@switch> show mld snooping membership detail
Instance: default-switch

Vlan: v1

Learning-Domain: default
Interface: ge-0/0/1.0, Groups: 1
    Group: ff05::1
        Group mode: Exclude
        Source: ::
        Last reported by: fe80::
        Group timeout:     259 Type: Dynamic
Interface: ge-0/0/2.0, Groups: 0

Meaning

The switch has multicast membership information for one VLAN on the switch, v1. MLD snooping might be enabled on other VLANs, but the switch does not have any multicast membership information for them.

  • The following information is provided about the group memberships for the VLAN:

    • Currently, the VLAN has membership in only one multicast group, ff05::1.

    • The host or hosts that have reported membership in the group are on interface ge-0/0/1.0.

    • The last host that reported membership in the group has address fe80::.

    • The interface group membership will time out in 259 seconds if no hosts respond to membership queries during this interval.

    • The group membership has been learned by MLD snooping, as indicated by Dynamic.

Verifying MLD Snooping Interfaces

Purpose

Display MLD snooping information for each interface on which MLD snooping is enabled.

Action

Enter the following command:

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user@switch>show mld snooping interface
Instance: default-switch

Vlan: v100

Learning-Domain: default
Interface: ge-0/0/1.0
    State:         Up Groups:      1
    Immediate leave: Off
    Router interface: no
Interface: ge-0/0/2.0
    State:         Up Groups:      0
    Immediate leave: Off
    Router interface: no

Configured Parameters:
MLD Query Interval: 125.0
MLD Query Response Interval: 10.0
MLD Last Member Query Interval: 1.0
MLD Robustness Count: 2

Meaning

MLD snooping is configured on one VLAN on the switch, v100. Each interface in each VLAN is listed and the following information is provided:

  • How many multicast groups the interface belongs to.

  • Whether immediate leave has been configured for the interface.

  • Whether the interface is a multicast-router interface.

The output also shows the configured parameters for the MLD querier.

Viewing MLD Snooping Statistics

Purpose

Display MLD snooping statistics, such as number of MLD queries, reports, and leaves received and how many of these MLD messages contained errors.

Action

Enter the following command:

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user@switch>show mld snooping statistics
Vlan: v1
MLD Message type            Received       Sent  Rx errors
Listener Query (v1/v2)             0          4          0
Listener Report (v1)             447          0          0
Listener Done (v1/v2)              0          0          0
Listener Report (v2)               0          0          0
Other Unknown types                                      0

Vlan: v2
MLD Message type            Received       Sent  Rx errors
Listener Query (v1/v2)             0          4          0
Listener Report (v1)             154          0          0
Listener Done (v1/v2)              0          0          0
Listener Report (v2)               0          0          0
Other Unknown types                                      0

Instance: default-switch
MLD Message type            Received       Sent  Rx errors
Listener Query (v1/v2)             0          8          0
Listener Report (v1)             601          0          0
Listener Done (v1/v2)              0          0          0
Listener Report (v2)               0          0          0
Other Unknown types                                      0

MLD Global Statistics
Bad Length                    0
Bad Checksum                  0
Bad Receive If                0
Rx non-local                  0
Timed out                     0

Meaning

The output shows how many MLD messages of each type—Queries, Done, Report—the switch received or transmitted on interfaces on which MLD snooping is enabled. For each message type, it also shows the number of MLD packets the switch received that had errors—for example, packets that do not conform to the MLDv1 or MLDv2 standards. If the Rx errors count increases, verify that the hosts are compliant with MLDv1 or MLDv2 standards. If the switch is unable to recognize the MLD message type for a packet, it counts the packet under Other Unknown types.

Viewing MLD Snooping Routing Information

Purpose

Display the next-hop information maintained in the multicast snooping forwarding table.

Action

Enter the following command:

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user@switch>show multicast snooping route
Nexthop Bulking: OFF

             Family: INET6

Group: ff00::/8
    Source: ::/128
    Vlan: v1

Group: ff02::1/128
    Source: ::/128
    Vlan: v1
        Downstream interface list:
        ge-1/0/16.0

Group: ff05::1/128
    Source: ::/128
    Vlan: v1
        Downstream interface list:
        ge-1/0/16.0

Group: ff06::1/128
    Source: ::/128
    Vlan: v1
        Downstream interface list:
        ge-1/0/16.0

Meaning

The output shows the next-hop interfaces for a given multicast group on a VLAN. For example, route ff02::1/128 on VLAN v1 has the next-hop interface ge-1/0/16.0.

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