Static routing

A route provides the device with the information it needs to forward a packet to a particular destination. A static route causes packets to be forwarded to a destination other than the configured default gateway.

By specifying through which interface the packet will leave and to which device the packet should be routed, static routes control the traffic exiting the device.

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 adding any additional burden on the source or the receivers.

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

If IP multicast is not used, the source is required to send more than one copy of a packet or individual copy to each receiver. In such case, high-bandwidth applications like video or stock where data is to be send more frequently and simultaneously, uses large portion of the available bandwidth. In these applications, the only efficient way of sending information to more than one receiver simultaneously is by using IP multicast.

Multicast group

Multicast is based on the concept of a group. An arbitrary group of receivers expresses an interest in receiving a particular data stream. This group does not have any physical or geographical boundaries - the hosts can be located anywhere on the internet. Hosts that are interested in receiving data flowing to a particular 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 group address or destination address of IP multicast traffic. The source address for multicast datagram is always the unicast source address.

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 there are no nodes 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 being listened to by the node with local routers, so that multicast packets can be forwarded to the network of the node.

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 are listening for all traffic to a specified IP multicast address.