In vSphere 6.0 and later, vSphere Distributed Switch supports basic and snooping models for filtering of multicast packets that are related to individual multicast groups. Choose a model according to the number of multicast groups to which the virtual machines on the switch subscribe.

Multicast Filtering Modes

In addition to the default basic mode for filtering multicast traffic, vSphere Distributed Switch 6.0.0 and later releases support multicast snooping that forwards multicast traffic in a more precise way based on the Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) messages from virtual machines.

Basic Multicast Filtering

In basic multicast filtering mode, a vSphere Standard Switch or vSphere Distributed Switch forwards multicast traffic for virtual machines according to the destination MAC address of the multicast group. When joining a multicast group, the guest operating system pushes the multicast MAC address of the group down to the network through the switch. The switch saves the mapping between the port and the destination multicast MAC address in a local forwarding table.

The switch does not interpret the IGMP messages that a virtual machine sends to join or leave a group. The switch sends them directly to the local multicast router, which then interprets them to join the virtual machine to or remove it from the group.

The basic mode has the following restrictions:

  • A virtual machine might receive packets from groups that it is not subscribed for because the switch forwards packets according to the destination MAC address of a multicast group, which can be potentially mapped up to 32 IP multicast groups.
  • A virtual machine that is subscribed for traffic from more than 32 multicast MAC addresses receives packets that it is not subscribed for because of a limitation in the forwarding model.
  • The switch does not filter packets according to source address as defined in IGMP version 3.

Multicast Snooping

In multicast snooping mode, a vSphere Distributed Switch provides IGMP and MLD snooping according to RFC 4541. The switch dispatches multicast traffic more precisely by using IP addresses. This mode supports IGMPv1, IGMPv2, and IGMPv3 for IPv4 multicast group addresses, and MLDv1 and MLDv2 for IPv6 multicast group addresses.

The switch dynamically detects the membership of a virtual machine. When a virtual machine sends a packet which contains IGMP or MLD membership information through a switch port, the switch creates a record about the destination IP address of the group, and in the case of IGMPv3, about a source IP address that the virtual machine prefers to receive traffic from. If a virtual machine does not renew its membership to a group within a certain period of time, the switch removes the entry for the group from the lookup records.

In multicast snooping mode of a distributed switch, a virtual machine can receive multicast traffic on a single switch port from up to 512 groups and 10 sources.
Note: In vSphere 6.7, the default multicast filtering mode is Basic. In vSphere 7.0, the default multicast filtering mode is IGMP/MLD snooping. When the DVS is upgraded to 7.0, the default multicast filtering mode will change from basic to IGMP/MLD snooping.

Enable Multicast Snooping on a vSphere Distributed Switch

Use multicast snooping on a vSphere Distributed Switch to forward traffic in a precise manner according to Internet Group Management Protocol (IGMP) or Multicast Listener Discovery (MLD) membership information that virtual machines send to subscribe for multicast traffic.

Use multicast snooping if virtualized workloads on the switch subscribe to more than 32 multicast groups or must receive traffic from specific source nodes. For information about the multicast filtering modes of vSphere Distributed Switch, see Multicast Filtering Modes.

Prerequisites

Verify that vSphere Distributed Switch is version 6.0.0 and later.

Procedure

  1. On the vSphere Client Home page, click Networking and navigate to the distributed switch.
  2. From the Actions menu, select Settings > Edit Settings.
  3. In the dialog box that displays the settings of the switch, click Advanced.
  4. From the Multicast filtering mode drop-down menu, select IGMP/MLD snooping, and click OK.

Results

Multicast snooping becomes active on hosts running ESXi 6.0 and later.

Edit the Query Time Interval for Multicast Snooping

When IGMP or MLD multicast snooping is enabled on a vSphere Distributed Switch, the switch sends general queries about the membership of virtual machines in case a snooping querier is not configured on the physical switch. On ESXi hosts that are attached to the distributed switch, you can edit the time interval in which the switch sends general queries.

The default time interval for sending snooping queries is 125 seconds.

Procedure

  1. In the vSphere Client, navigate to the host.
  2. On the Configure tab, expand System and select Advanced System Settings.
  3. Click Edit.
  4. Locate the Net.IGMPQueryInterval system setting and enter a new value in seconds for the setting.
  5. Click OK

Edit the Number of Source IP Addresses for IGMP and MLD

When you enable IGMP or MLD multicast snooping on a vSphere Distributed Switch, you can edit the maximum number of IP sources from which the members of a multicast group receive packets.

Procedure

  1. In the vSphere Client, navigate to the host.
  2. On the Configure tab, expand System and select Advanced System Settings.
  3. Click Edit.
  4. Locate the Net.IGMPV3MaxSrcIPNum or Net.MLDV2MaxSrcIPNum system setting and enter a new value between 1 and 32 for the setting.
  5. Click OK.