Static Layer 2 Multicast

Background

Multicast data can be transmitted to user terminals over an IP bearer network in either dynamic or static multicast mode.

• In dynamic multicast mode, a device starts to receive and deliver a multicast group's data after receiving the first Report message for the group. The device stops receiving the multicast group's data after receiving the last Leave message. The dynamic multicast mode has both an advantage and a disadvantage:

  • Advantage: It reduces bandwidth consumption by restricting multicast traffic.
  • Disadvantage: It introduces a delay when a user switches a channel.

• In static multicast mode, multicast forwarding entries are configured for each multicast group on a device. A multicast group's data is delivered to a device, regardless of whether users are requesting the data from this device. The static multicast mode has the following advantages and disadvantages:

  • Advantages:
    • Multicast routes are fixed, and multicast paths exist regardless of whether there are multicast data receivers. Users can change channels without delays, improving user experience.
    • Multicast source and group ranges are easy to manage because multicast paths are stable.
    • The delay when data is first forwarded is minimal because static routes already exist and do not need to be established the way dynamic multicast routes do.
  • Disadvantages:
    • Each device on a multicast data transmission path must be manually configured. The configuration workload is heavy.
    • Sub-optimal multicast forwarding paths may be generated because downstream ports are manually specified on each device.
    • When a network topology or unicast routes change, static multicast paths may need to be reconfigured. The configuration workload is heavy.
    • Multicast routes exist even when no multicast data needs to be forwarded. This wastes network resources and creates high bandwidth requirements.

A Layer 2 multicast forwarding table can be dynamically built using IGMP snooping or be manually configured. Choose the dynamic or static mode based on network quality requirements and demanded service types.

If network bandwidth is sufficient and hosts require multicast data for specific multicast groups from a router port for a long period of time, choose static Layer 2 multicast to implement stable multicast data transmission on a metropolitan area network (MAN) or bearer network. After static Layer 2 multicast is deployed on a device, multicast entries on the device do not age and users attached to the device can stably receive multicast data for specific multicast groups.

Related Concepts

Static router ports or member ports are used in static Layer 2 multicast.

• Static router ports are used to receive multicast traffic.
• Static member ports are used to send data for specific multicast groups.

Deployment Scenarios

Static Layer 2 multicast can be used on VLANs and VPLS networks.

Benefits