TP-Link T1500G-8T T1500G-10PSUN V1 User Guide - Page 102
IPv4 Multicast Address, Multicast IP address range, Description
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3. Each user can join and leave the multicast group at any time; 4. Real time is highly demanded and certain packets drop is allowed. IPv4 Multicast Address 1. IPv4 Multicast IP Address: As specified by IANA (Internet Assigned Numbers Authority), Class D IP addresses are used as destination addresses of multicast packets. The multicast IP addresses range from 224.0.0.0~239.255.255.255. The following table displays the range and description of several special multicast IP addresses. Multicast IP address range Description 224.0.0.0~224.0.0.255 Reserved multicast addresses for routing protocols and other network protocols 224.0.1.0~224.0.1.255 Addresses for video conferencing 239.0.0.0 239.255.255.255 ~ Local management multicast addresses, which are used in the local network only Table 8-1 Range of the special multicast IP 2. IPv4 Multicast MAC Address: When a unicast packet is transmitted in an Ethernet network, the destination MAC address is the MAC address of the receiver. When a multicast packet is transmitted in an Ethernet network, the destination is not a receiver but a group with uncertain number of members, so a multicast MAC address, a logical MAC address, is needed to be used as the destination address. As stipulated by IANA, the high-order 24 bits of a multicast MAC address begins with 01-00-5E while the low-order 23 bits of a multicast MAC address are the low-order 23 bits of the multicast IP address. The mapping relationship is described as Figure 8-2. Figure 8-2 Mapping relationship between multicast IPv4 address and multicast MAC address The high-order 4 bits of the IP multicast address are 1110, identifying the multicast group. Only 23 bits of the remaining low-order 28 bits are mapped to a multicast MAC address. In that way, 5 bits of the IP multicast address is not utilized. As a result, 32 IP multicast addresses are mapped to the same MAC addresses. 92