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Verifying IGMP Snooping on EX Series Switches

 

Internet Group Management Protocol (IGMP) snooping constrains the flooding of IPv4 multicast traffic on VLANs on a switch. This topic describes how to verify IGMP snooping operation on the switch.

It covers:

Verifying IGMP Snooping Memberships

Purpose

Determine group memberships, multicast-router interfaces, host IGMP versions, and the current values of timeout counters.

Action

Enter the following command:

Meaning

The switch has multicast membership information for one VLAN on the switch, vlan2. IGMP snooping might be enabled on other VLANs, but the switch does not have any multicast membership information for them. The following information is provided:

  • Information on the multicast-router interfaces for the VLAN—in this case, ge-1/0/0.0. The multicast-router interface has been learned by IGMP snooping, as indicated by the dynamic value. The timeout value shows how many seconds from now the interface will be removed from the multicast forwarding table if the switch does not receive IGMP queries or Protocol Independent Multicast (PIM) updates on the interface.

  • Information about the group memberships for the VLAN:

    • Currently, the VLAN has membership in only one multicast group, 233.252.0.1.

    • The host or hosts that have reported membership in the group are on interface ge-1/0/17.0. The last host that reported membership in the group has address 10.0.0.90. The number of hosts belonging to the group on the interface is shown in the Receiver count field, which is displayed only when host tracking is enabled if immediate leave is configured on the VLAN.

    • The Uptime field shows that the multicast group has been active on the interface for 19 seconds. The interface group membership will time out in 259 seconds if no hosts respond to membership queries during this interval. The Flags field shows the lowest version of IGMP used by a host that is currently a member of the group, which in this case is IGMP version 3 (IGMPv3).

    • Because the interface has IGMPv3 hosts on it, the source addresses from which the IGMPv3 hosts want to receive group multicast traffic are shown (addresses 10.2.11.5 and 10.2.11.12). The timeout value for the interface group membership is derived from the largest timeout value for all sources addresses for the group.

Viewing IGMP Snooping Statistics

Purpose

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

Action

Enter the following command:

Meaning

The output shows how many IGMP messages of each type—Queries, Reports, Leaves—the switch received or transmitted on interfaces on which IGMP snooping is enabled. For each message type, it also shows the number of IGMP packets the switch received that had errors—for example, packets that do not conform to the IGMPv1, IGMPv2, or IGMPv3 standards. If the Recv Errors count increases, verify that the hosts are compliant with IGMP standards. If the switch is unable to recognize the IGMP message type for a packet, it counts the packet under Receive unknown.

Viewing IGMP Snooping Routing Information

Purpose

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

Action

Enter the following command:

Meaning

The output shows the next-hop interfaces for a given multicast group on a VLAN.