You can configure multicast on a tier-0 gateway for an IPv4 network to send the same multicast data to a group of recipients. In a multicast environment, any host, regardless of whether it is a member of a group, can send to a group. However, only the members of a group will receive packets sent to that group.

The multicast feature has the following capabilities and limitations:
  • PIM Sparse Mode with IGMPv2.
  • No Rendezvous Point (RP) or Bootstrap Router (BSR) functionality on NSX-T. However, RP information can be learned via PIM Bootstrap Messages (BSMs). In addition, a Static RP can be configured.

    When a Static RP is configured, it serves as the RP for all multicast groups (224/4). If candidate RPs learned from BSMs advertise candidacy for the same group range, the Static RP is preferred. However, if candidate RPs advertise candidacy for a specific group or range of groups, they are preferred as the RP for those groups.

  • The Reverse Path Forwarding (RPF) check for all multicast-specific IPs (senders of data traffic, BSRs, RPs) requires that a route to each of them exists. In NSX-T Data Center 3.0.0, reachability via the default route is not supported. Starting with NSX-T Data Center 3.0.1, reachability via the default route is also supported.
  • The RPF check requires a route to each multicast-specific IP with an IP address as the next hop. Reachability via device routes, where the next hop is an interface index, is not supported.
  • Tier-0 gateway only.
  • Supported on only one uplink on a tier-0 gateway.
  • Active-Cold Standby only is supported.
  • The NSX Edge cluster can be in active-active or active-standby mode. When the cluster is in active-active mode, two of the cluster members will run multicast in active-cold standby mode. You can run the CLI command get mcast high-availability role on each Edge to identify the two nodes participating in multicast. Also note that since unicast reachability to NSX-T in an active-active cluster is via ECMP, it is imperative that the northbound PIM router selects the ECMP path that matches a PIM neighbor to send PIM Join/Prune messages to NSX-T. In this way it will select the active Edge which is running PIM.
  • East-west multicast replication: up to 4 VTEP segments for maximum replication efficiency.
  • ESXi host and NSX Edge only (KVM not supported).
  • Layer 2 bridge attached to a downlink segment not supported.
  • Edge Firewall services are not supported for multicast.
  • Multi-site (federation) not supported.
  • Multi-VRF not supported.

Multicast Configuration Prerequisites

Underlay network configurations:
  • Acquire a multicast address range from your network administrator. This will be used to configure the Multicast Replication Range when you configure multicast on a tier-0 gateway (see Configure Multicast).
  • Enable IGMP snooping on the layer 2 switches to which GENEVE participating hosts are attached. If IGMP snooping is enabled on layer 2, IGMP querier must be enabled on the router or layer 3 switch with connectivity to multicast enabled networks.

Multicast Configuration Steps

  1. Create an IGMP profile. See Create an IGMP Profile.
  2. Optionally create a PIM profile to configure a Static Rendezvous Point (RP). See Create a PIM Profile.
  3. Configure a tier-0 gateway to support multicast. See Add a Tier-0 Gateway and Configure Multicast