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Multicast IGMP Snooping and PIM Design and Implementation


Use this design to configure Internet Group Management Protocol (IGMP) and Physical Interface Module (PIM) in your fabric to improve multicast replication. IGMP snooping preserves bandwidth because multicast traffic is forwarded only on interfaces where there are IGMP listeners. For instance, every leaf device does not need to receive every instance of multicast traffic.

For an overview of multicast, see Multicast Optimizations

In this design, we are using an external PIM gateway, which extends multicast beyond the data center, and is useful in DCI implementations.

The following sections show how to configure and verify multicast:

Configuring IGMP Snooping

In this design, we are using IGMP snooping to constrain multicast traffic in a broadcast domain to interested receivers and multicast devices.

To configure IGMP snooping:

  1. Configure IGMP snooping on all VXLAN enabled VLANs on the leafs. The current implementation does not support IGMP snooping on selected VXLAN enabled VLANs.

Verifying IGMP Snooping

  1. Verify the local IGMP snooping state on the leaf.
    user@leaf-2> show igmp snooping membership vlan BD-3
    user@leaf-2> show evpn igmp-snooping database l2-domain-id 100003
  2. Verify that the leaf is advertising the EVPN Type 7 route where IGMP is snooped.
    user@leaf-2> show route table __default_evpn__.evpn.0 match-prefix 7:*100003*225.0.1.[12]*
  3. Verify that the leaf is advertising the EVPN Type 6 route and the multihomed ESI peer device for the multicast group.
    user@leaf-2> show route table default-switch.evpn.0 match-prefix 6:*100003*225.0.1.[12]*

Configuring PIM

  1. To configure inter-VNI multicast routing at the spine, create a routing instance for a tenant (a leaf device) named VRF-1. Configure the following in the routing instance:
    • Add the IRB interfaces to the leaf devices.

    • Enable PIM and configure the local address for this spine as the rendezvous point (RP).

    • Enable PIM on the IRB interfaces.

    Spine 1:

  2. Configure multicast routing on another spine. Configure a corresponding VRF routing instance for the same tenant as in step 6.
    • Add the IRB interfaces toward the leaf devices.

    • Enable PIM and configure the RP address on spine 1 as the static RP.

    • Enable PIM on the IRB interfaces.

    Spine 2:

Verifying PIM

  1. On Spine 1, verify the EVPN routing table on the VRF-1 routing instance.
    user@spine-1> show route table VRF-1.inet6.0 protocol evpn
  2. On spine 1, check the PIM control plane on the RP, and verify that:
    • PIM joins are created from Type 6 routes that are generated by leaf devices.

    • IGMP reports are coming from non-IGMP snooping capable leaf devices.

    user@spine-1> show pim join instance VRF-1 extensive
  3. On the spine that is configured as the PIM DR, verify the multicast forwarding state from the spine to the tenant VRF. To do so:
    1. Enter show pim interfaces instance on all spines, and check the State column to see which IRB interface is a DR.
      user@spine-1> show pim interfaces instance VRF-1
    2. On the PIM DR, display the multicast forwarding state.
      user@spine-2> show multicast route extensive instance VRF-1 group