Note	We recommend that you do not disable IGMP snooping on the device. If you disable IGMP snooping, you might see reduced multicast performance because of excessive false flooding within the device.

IGMP snooping software examines Layer 2 IP multicast traffic within a VLAN to discover the ports where interested receivers reside. Using the port information, IGMP snooping can reduce bandwidth consumption in a multi-access LAN environment to avoid flooding the entire VLAN. IGMP snooping tracks which ports are attached to multicast-capable routers to help the routers forward IGMP membership reports. The IGMP snooping software responds to topology change notifications. By default, IGMP snooping is enabled on the device.

This figure shows an IGMP snooping switch that sits between the host and the IGMP router. The IGMP snooping switch snoops the IGMP membership reports and Leave messages and forwards them only when necessary to the connected IGMP routers.

The IGMP snooping software operates upon IGMPv1, IGMPv2, and IGMPv3 control plane packets where Layer 3 control plane packets are intercepted and influence the Layer 2 forwarding behavior.

The Cisco NX-OS IGMP snooping software has the following proprietary features:

• Source filtering that allows forwarding of multicast packets based on destination and source IP addresses

• Multicast forwarding based on IP addresses rather than the MAC address

• Multicast forwarding alternately based on the MAC address

For more information about IGMP snooping, see RFC 4541.

IGMP snooping has the following prerequisites:

• You are logged onto the device.

• For global commands, you are in the correct virtual routing and forwarding (VRF) mode. The default configuration mode shown in the examples in this chapter applies to the default VRF.

IGMP snooping has the following guidelines and limitations:

• Cisco Nexus 9000 Series switches support IGMP snooping for IPv4 but do not support MLD snooping for IPv6.

• IGMP snooping is not supported with PVLAN.

• Layer 3 IPv6 multicast routing is not supported.

• Layer 2 IPv6 multicast packets will be flooded on the incoming VLAN.

• Cisco Nexus 9508 and 9504 platform switches with N9K-X9636C-R, N9K-X9636Q-R, and N9K-X9636C-RX line cards support IGMP snooping with vPCs.

• IGMP snooping configuration must be identical on both vPC peers in a vPC pair. Either enable or disable IGMP snooping on both vPC peers.

  Note

  Enabling or disabling IGMP snooping on both vPC peers also enables the forwarding of IGMP queries from different MVR source VLANs into the same MVR receiver VLAN. The resulting IGMP queries may send out queries with different versions and query interval. If you prefer to maintain the behavior prior to Cisco NX-OS Release 7.0(3)I3(1) use the mvr-suppress-query vlan <id> command.

• In releases prior to Cisco NX-OS Release 7.0(3)I3(1) if you are configuring vPC peers, the differences in the IGMP snooping configuration options between the two devices have the following results:

  • If IGMP snooping is enabled on one device but not on the other, the device on which snooping is disabled floods all multicast traffic.

  • A difference in multicast router or static group configuration can cause traffic loss.

  • The fast leave, explicit tracking, and report suppression options can differ if they are used for forwarding traffic.

  • If a query parameter is different between the devices, one device expires the multicast state faster while the other device continues to forward. This difference results in either traffic loss or forwarding for an extended period.

  • If an IGMP snooping querier is configured on both devices, only one of them will be active because an IGMP snooping querier shuts down if a query is seen in the traffic.

• You must enable the ip igmp snooping group-timeout command when you use the ip igmp snooping proxy general-queries command. We recommend that you set it to "never". Otherwise, you might experience multicast packet loss.

• The command "ip igmp snooping proxy general-queries" generates G reports and not (S,G) information report.

• All external multicast router ports (either statically configured or dynamically learned) use the global ltl index. As a result, traffic in VLAN X goes out on the multicast router ports in both VLAN X and VLAN Y, in case both multicast router ports (Layer 2 trunks) carry both VLAN X and VLAN Y.

• When you modify the route-map to deny the multicast group, which is statically bound to the interface; the subsequent IGMP reports are rejected by the local groups and the groups start ageing. The IGMP leave message for the groups is allowed without any impact. This is a known and expected behaviour.

You can display the IGMP snooping statistics using these commands.

You can clear the IGMP snooping statistics using these commands.

Note	The configurations in this section apply only after you create the specified VLAN. See the Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide for information on creating VLANs.

The following example shows how to configure the IGMP snooping parameters:

config t
  ip igmp snooping
  vlan configuration 2
    ip igmp snooping
    ip igmp snooping explicit-tracking
    ip igmp snooping fast-leave
    ip igmp snooping last-member-query-interval 3
    ip igmp snooping querier 172.20.52.106
    ip igmp snooping report-suppression
    ip igmp snooping mrouter interface ethernet 2/1
    ip igmp snooping static-group 230.0.0.1 interface ethernet 2/1
    ip igmp snooping link-local-groups-suppression
    ip igmp snooping v3-report-suppression

The following example shows how to configure prefix lists and use them to filter IGMP snooping reports:

ip prefix-list plist seq 5 permit 224.1.1.1/32 
ip prefix-list plist seq 10 permit 224.1.1.2/32 
ip prefix-list plist seq 15 deny 224.1.1.3/32  
ip prefix-list plist seq 20 deny 225.0.0.0/8 eq 32

vlan configuration 2
  ip igmp snooping report-policy prefix-list plist interface Ethernet 2/2
  ip igmp snooping report-policy prefix-list plist interface Ethernet 2/3

In the above example, the prefix-list permits 224.1.1.1 and 224.1.1.2 but rejects 224.1.1.3 and all the groups in the 225.0.0.0/8 range. The prefix-list is an implicit "deny" if there is no match. If you wish to permit everything else, add ip prefix-list plist seq 30 permit 224.0.0.0/4 eq 32.

The following example shows how to configure route maps and use them to filter IGMP snooping reports:

route-map rmap permit 10
  match ip multicast group 224.1.1.1/32 
route-map rmap permit 20
  match ip multicast group 224.1.1.2/32 
route-map rmap deny 30
  match ip multicast group 224.1.1.3/32
route-map rmap deny 40
  match ip multicast group 225.0.0.0/8

vlan configuration 2
  ip igmp snooping report-policy route-map rmap interface Ethernet 2/4
  ip igmp snooping report-policy route-map rmap interface Ethernet 2/5

In the above example, the route-map permits 224.1.1.1 and 224.1.1.2 but rejects 224.1.1.3 and all the groups in the 225.0.0.0/8 range. The route-map is an implicit "deny" if there is no match. If you wish to permit everything else, add route-map rmap permit 50 match ip multicast group 224.0.0.0/4.