A multicast address is designed to enable the delivery of datagrams to a set of hosts that have been configured as members of a multicast group in various scattered subnetworks.

The MBONE is a virtual network. It is layered on top of portions of the physical Internet to support routing of IP multicast packets. The network is composed of islands that can directly support IP multicast, such as multicast LANs like Ethernet, linked by virtual point-to-point links called "tunnels". The tunnel endpoints are typically workstation-class machines having operating system support for IP multicast.

IP multicast packets are encapsulated for transmission through tunnels, so that they look like normal unicast datagrams to intervening routers and subnets. The multicast router at the other end of the tunnel receives the packet, strips off the encapsulating IP header, and forwards the packet as appropriate.

The only difference between a multicast IP packet and a unicast IP packet is the presence of a "group address" in the Destination Address field of the IP header. Multicasting has a Class D destination address format (224.0.0.0-239.255.255.255).

The majority of Internet applications rely on point-to-point transmission. Multicast IP conserves bandwidth by forcing the network to do packet replication only when necessary.

Distance Vector Multicast Routing Protocol (DVMRP) is a distance-vector routing protocol designed to support the forwarding of multicast datagrams through an internetwork. DVMRP was first defined in RFC-1075.

Multicast Open Shortest Path First (MOSPF) is the IP Multicast extension of the Open Shortest Path First (OSPF) unicast routing protocol. It is defined in RFC 1584. Each router can calculate a spanning tree with the multicast source at the root and the group members as leaves. This tree is the path that is used to route multicast traffic from the source to each of the group members.

Real-Time Streaming Protocol (RTSP) is an application-level protocol for control over the delivery of data with real-time properties to enable controlled, on-demand delivery of real-time data, such as audio and video.

Real-Time Transport Protocol (RTP) provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services.

Some of the more popular uses of multimedia are real-time interactive applications, such as desktop video and audio conferencing, shared white boards, and animated simulations. Even when data compression is used, multimedia applications require lots of bandwidth. With IP multicast it would be easy to support thousands of recipients, each sitting at his/her own desk.

• A high percentage of broadcast traffic can indicate a broadcast storm. To temporarily correct this problem, you can create a customized packet filter to filter out the broadcast traffic being transmitted by the port, or you can disable the port. However, to solve the problem, you must discover what device on the network is generating the broadcast traffic.
• A high percentage of error rates for a port can indicate a transceiver problem or a bad line. On a shared Ethernet segment, if utilization is 40 percent or higher, you need to reconfigure the network to balance the load better.
• A high percentage of excessive collisions on a port can indicate high traffic levels, or possibly a transceiver problem on that port. A high rate of FCS errors for a port can indicate a hardware problem or a bad line.
• A port can go down because of a hardware condition or a port disconnection. You may find that some ports go up and down daily as people plug laptops into the network.

Multicast Extensions to OSPF (mospf)

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