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Multicast routing

This page provides details about multicast routing.

This section covers the following topics:

  • Enable/Disable multicast forwarding
  • Configure static multicast routes
  • Viewing routes
  • Removing Routes

To reach the configuration menu from the main menu, select: Option 3 (Route Configuration) > Option 2 (Configure Multicast Routing)

The following screen appears:

Multicast Routing Configuration

    1.  Enable/Disable Multicast forwarding
    2.  Configure static-routes
    3.  Exit

    Select Menu Number:

IP Multicast

Internet Protocol (IP) multicast is a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to thousands of recipients and homes. IP multicast delivers source traffic to multiple receivers without additional burden on the source or the receivers.

Applications like videoconferencing, corporate communications, distance learning, software distribution, stock quotes, and news use IP multicasting.

If IP multicast isn't used, a source must send more than one copy of a packet or an individual copy to each receiver. In such cases, high-bandwidth applications like video or stock where data is sent more frequently and simultaneously, use a large portion of the available bandwidth. In these applications, the only efficient way of simultaneously sending information to more than one receiver is by using IP multicast.

Multicast Group

Multicast is based on the concept of a group. An arbitrary group of receivers is interested in receiving a specific data stream. This group does not have any physical or geographical boundaries. The hosts can be located anywhere on the internet. Hosts interested in receiving data flow to a specific group must join the group. Hosts must be a member of the group to receive the data stream.

IP Multicast Addresses

Multicast addresses specify an arbitrary group of IP hosts that have joined the group and want to receive traffic sent to this group.

IP Class D Addresses

The Internet Assigned Numbers Authority (IANA) controls the assignment of IP multicast addresses. Multicast addresses fall in Class D address space ranging from to

This address range is only for the IP multicast traffic's group address or destination address. The source address for multicast datagrams is always the unicast source address.

Multicast Forwarding

In multicast routing, the source sends traffic to a group of hosts represented by a multicast group address. The multicast router must determine which direction is upstream (towards the source) and which direction (or directions) is downstream. The router replicates the packet and forwards the traffic down the appropriate downstream paths if there are multiple downstream paths. This isn't necessarily all paths.

Turn on or turn off Multicast forwarding

With multicast forwarding, a router forwards multicast traffic to networks where other multicast devices are listening. Multicast forwarding prevents the forwarding of multicast traffic to networks where no nodes are listening.

For multicast forwarding to work across inter-networks, nodes and routers must be multicast-capable.

A multicast capable node must be able to:

  • Send and receive multicast packets.
  • Register the multicast addresses that the node is listening for with the local routers, so multicast packets can be forwarded to the network.

IP multicasting applications that send multicast traffic must construct IP packets with the appropriate IP multicast address as the destination IP Address. IP multicasting applications that receive multicast traffic must inform the TCP/ IP protocol that they're listening for all traffic to a specified IP multicast address.

Setting up IP Multicast forwarding

Configuring multicast forwarding is a two-step process:

  • Enable multicast forwarding (both the modes)
  • Configure multicast routes (only in Gateway mode)

To enable multicast forwarding, select: Option 3 (Route Configuration) > option 2 (Configure Multicast Routing) > option 1 (enable/Disable Multicast Forwarding) and execute the following command:

enable multicast-forwarding