IP multicast technology and programming (1)

IP multicast is also called Multicast) technology, which allows one or more multicast sources to send a single packet to multiple hosts once) TCP/IP network technology. Multicast, as a one-to-multiple-point communication, is one of the effective ways to save network bandwidth. In Network Audio/Video Broadcast applications, when a node signal needs to be transmitted to multiple nodes, whether it is through repeated point-to-point communication or broadcast, network bandwidth is a serious waste. Only multicast is the best choice. Multicast enables one or more multicast sources to send only data packets to a specific multicast group, and only the host that joins the multicast group can receive data packets. Currently, IP multicast technology is widely used in network audio/video broadcast, AOD/VOD, network video conferencing, multimedia distance education, and "push" technology such as stock quotations) and Virtual Reality games.

I. Introduction to IP multicast technology
1. IP multicast address and multicast group

IP multicast communication must depend on the IP multicast address. In IPv4, It is a Class d ip address ranging from 224.0.0.0 to 239.255.255.255, it is divided into three categories: Local Link multicast address, reserved multicast address, and management permission multicast address. The local link multicast address ranges from 224.0.0.0 ~ 224.0.0.255 is the address reserved for the routing protocol and other purposes. The Router does not forward IP packets in this range. The reserved multicast address is 224.0.1.0 ~ 238.255.255.255, which can be used on a global scale such as the Internet) or network protocol. The management permission multicast address is 239.0.0.0 ~ 239.00000000255, which can be used within an organization. It is similar to a private IP address and cannot be used on the Internet. It can restrict the multicast range.

All Hosts that receive multicast data packets using the same IP address constitute a host group, also known as multicast groups. Members of a multicast group change at any time. A host can join or leave a multicast group at any time. The number and geographic location of multicast group members are not limited, A host can also belong to several multicast groups. In addition, a host that does not belong to a multicast group can also send data packets to the multicast group.

2. Hardware Support for IP multicast technology

To implement IP multicast communication, the routers, hubs, switches, and hosts between multicast sources and receivers must support IP multicast. Currently, IP multicast technology has been widely supported by hardware and software vendors.

1) Host

Platforms that support IP multicast communication include Windows CE 2.1, Windows 95, Windows 98, Windows NT 4, and Windows 2000. All hosts running these operating systems can perform IP multicast communication. In addition, almost all newly produced NICs provide support for IP multicast.

2) hubs and switches

Currently, most hubs and switches simply use multicast data as broadcasts for sending and receiving, but some medium and high-end switches provide support for IP multicast. For example, the 802.1p or IGMP multicast filtering function can be enabled on the 3COM SuperStack 3 Swith 3300 Switch to forward multicast data packets only to the ports that have detected IGMP data packets.

3) Router

Multicast Communication requires that all routers between the source and target nodes must support the Internet Group Management Protocol (IGMP) and Multicast Routing Protocol (PIM and DVMRP.

When a host wants to join a multicast group, the "host Member Report" IGMP message is sent to the multicast router. When the multicast router receives the data sent to that multicast group, it forwards the data to all multicast hosts. The multicast router periodically sends an IGMP message for "host Member query" to query the multicast host from the subnet. If a multicast group has no members, the multicast group data is stopped. In addition, when a host that supports IGMP v2, such as a Windows 98/2000 computer, exits from a multicast group, an IGMP message is sent to the router, to notify the router to stop forwarding data of the multicast group. However, the vro stops forwarding multicast group data to the subnet only when all hosts in the subnet exit from a multicast group.

Using the multicast routing protocol, A vro can establish a multicast route table from the multicast source node to all target nodes to forward multicast data packets between subnets. For example, the PIM protocol is an independent multicast protocol. It has two types: sparse-mode in sparse mode and dense-mode in dense mode ). Take the Cisco 2621 router as an example. The basic settings for enabling IP multicast forwarding are as follows:

C2621 (config) # ip multicast-routing

C2621 (config) # int f0/0 configure Fast Ethernet port 0

C2621 (config-if) # ip pim dense-mode or sparse-mode) Start PIM and activate IGMP

C2621 (config-if) # int f0/1 configure Fast Ethernet Port 1

C2621 (config-if) # ip pim dense-mode or sparse-mode)