Accton Technology ES4710BD manual Common Multicast Configurations, Application of Multicast

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multicast group address in the destination address field of the IP packet. The multicast model differs from the unicast model in that a multicast packet must be forwarded to several external interfaces to send the packet to all receiving stations, i.e., multicast forwarding is more complex than unicast forwarding.

To ensure the multicast packets reach the routers using the shortest route, the multicast protocols must check the receiving interfaces of the multicast packets against the unicast route table or route table dedicated for multicast (such as a DVMRP route table). This checking mechanism is the base for most multicast routing protocols to perform forwarding, and is called Reverse Path Forwarding (RPF). Multicast routers use the source address of an arrived multicast packet to query the unicast route table or an independent multicast route table to make sure the ingress interface from which the packet arrived is in the shortest route from the receiving station to the source address. If an active tree is used, the source address is the address of source host sending the multicast packet; if a shared tree is used, the source address is the root address of that shared tree. When a multicast packet arrives at a router, the packet will be forwarded according to the multicast forwarding rules if the RPF check is ok; otherwise, the packet will be discarded.

19.1.4 Application of Multicast

IP multicast technology effectively solved the problem of one sender vs. multiple receivers, fulfilling the high efficiency data transmission from one point to multiple points in the IP network, and can significantly save the network bandwidth and reduce network traffic. The multicast feature can be conveniently used to provide some new value-added services, including online live broadcast, network TV, remote education, remote medical service, network radio, real-time video/audio meeting that can be summarized in the following three fields:

1)Multimedia and stream applications.

2)Data warehouse and financial (like stocks) applications.

3)Any point-to-multiple-points data distribution applications.

With the increasing of multimedia services in the IP network, multicast represents great market potential, and multicast service is widely used and spreading quickly.

19.2Common Multicast Configurations

19.2.1 Common Multicast Configuration Commands

zshow ip mroute

19.2.1.1 show ip mroute

Command: show ip mroute [group_address] [source_address]

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