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Verifying IGMP Snooping (CLI Procedure)
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
- Verifying IGMP Snooping VLANs
- Viewing IGMP Snooping Statistics
- Viewing IGMP Snooping Routing Information
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:
user@switch> show igmp-snooping membership detail VLAN: vlan2 Tag: 2 (Index: 3) Router interfaces: ge-1/0/0.0 dynamic Uptime: 00:14:24 timeout: 253 Group: 225.0.0.1 ge-1/0/17.0 timeout: 259 Last reporter: 13.0.0.90 Receiver count: 1, Flags: <V3-hosts> Include source: 10.2.11.5, 10.2.11.12
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 dynamic. 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, 225.0.0.1.
- The host or hosts that have reported membership in the group are on interface ge-1/0/17.0. The interface group membership will time out in 259 seconds if no hosts respond to membership queries during this interval.
- The last host that reported membership in the group has address 13.0.0.90. 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 because immediate leave has been configured on the VLAN. 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 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.
Verifying IGMP Snooping VLANs
Purpose
Verify that IGMP snooping is enabled on a VLAN and display IGMP snooping information for each VLAN on which IGMP snooping is enabled.
Action
Enter the following command:
user@switch> show igmp-snooping vlans detail VLAN: v10, Tag: 10 Interface: ge-1/0/0.0, tagged, Groups: 0, Router Interface: ge-1/0/30.0, untagged, Groups: 1 Interface: ge-12/0/30.0, untagged, Groups: 0 VLAN: v20, Tag: 20 Interface: ge-1/0/0.0, tagged, Groups: 0, Router Interface: ge-1/0/31.0, untagged, Groups: 0, Reporters: 0 Interface: ge-12/0/31.0, untagged, Groups: 1, Reporters: 1
Meaning
IGMP snooping is configured on two VLANs on the switch: v10 and v20. Each interface in each VLAN is listed and the following information is provided:
- Whether the interface is a trunk (tagged) or access (untagged) interface.
- How many multicast groups the interface belongs to.
- Whether the interface is a multicast-router interface (Router).
- How many hosts are reporting membership in the group on the interface. The Reporters field is included only if immediate leave is configured on the VLAN.
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:
user@switch> show igmp-snooping statistics Bad length: 0 Bad checksum: 0 Invalid interface: 0 Not local: 0 Receive unknown: 0 Timed out: 0 IGMP Type Received Transmitted Recv Errors Queries: 74295 0 0 Reports: 18148423 0 16333523 Leaves: 0 0 0 Other: 0 0 0
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:
user@switch> show igmp-snooping route detail VLAN Group Next-hop v100 224.0.0.0, * 1323 Interfaces: ge-0/0/0.0 VLAN Group Next-hop v100 226.0.0.1, * 1322 Interfaces: ge-0/0/0.0, ge-0/0/1.0, ge-0/0/47.0
Meaning
The output shows the next-hop interfaces for a given multicast group on a VLAN. For example, route 226.0.0.1 on v100 has next-hop interfaces ge-0/0/0.0, ge-0/0/1.0, and ge-0/0/47.0.
