What is the range of multicast addresses?

Multicast addresses use Class D IP addresses, ranging from "224.0.0.0" to "239.255.255.255", and some addresses have specific uses, for example: "224.0.0.1" is for all hosts Address, "224.0.0.2" is the address of all routers etc.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

The destination address of multicast packets uses Class D IP addresses. Class D addresses cannot appear in the source IP address field of IP packets.

Class D IP address does not distinguish between network address and host address. It is a specially reserved address with an address range of 224.0.0.0~239.255.255.255. Class D IP addresses are mainly used in multicast (Multicast, also known as multicast) as a multicast group IP address.

During the unicast data transmission process, the transmission path of a data packet is routed from the source address to the destination address, and is transmitted in the IP network using the "hop-by-hop" principle. However, in the IP multicast ring, the destination address of the data packet is not one, but a group, forming a group address. All information recipients join a group, and once they join, data flowing to the group address immediately begins to be transmitted to the recipients, and all members of the group can receive the data packets. Members in a multicast group are dynamic, and hosts can join and leave the multicast group at any time.

Multicast address classification

Multicast groups can be permanent or temporary. Some of the multicast group addresses are officially assigned and are called permanent multicast groups. What remains unchanged in a permanent multicast group is its IP address, and the composition of members in the group can change. The number of members in a permanent multicast group can be arbitrary, or even zero. IP multicast addresses that are not reserved for permanent multicast groups can be used by temporary multicast groups.

224.0.0.0~224.0.0.255 are reserved multicast addresses (permanent group addresses). Address 224.0.0.0 is reserved and not allocated. Other addresses are used by routing protocols;

224.0. 1.0~224.0.1.255 are public multicast addresses, which can be used on the Internet;

224.0.2.0~238.255.255.255 are multicast addresses available to users (temporary group addresses), which are valid within the entire network;

239.0.0.0~239.255.255.255 are local management multicast addresses, which are only valid within a specific local range.

Multicast address list

The list is as follows:

224.0.0.0 Base address (reserved)

224.0.0.1 All hosts The address of all multicast routers (including all router addresses)

224.0.0.2 The address of all multicast routers

224.0.0.3 Not assigned

224.0.0.4 dvmrp router

224.0.0.5 all ospf router

224.0.0.6 ospf DR/BDR

224.0.0.7 st router

224.0.0.8 st host

224.0. 0.9 rip-2 router

224.0.0.10 Eigrp router

224.0.0.11 active proxy

224.0.0.12 dhcp server/relay proxy

224.0. 0.13 All pim routers

224.0.0.14 rsvp encapsulation

224.0.0.15 All cbt routers

224.0.0.16 Specify sbm

224.0.0.17 All sbms

224.0.0.18 vrrp

224.0.0.22 IGMPv3

When Ethernet transmits unicast IP messages, the destination mac address uses the mac address of the receiver. However, when transmitting multicast messages, the transmission destination is no longer a specific receiver, but a group with uncertain members, so the multicast MAC address is used. The multicast mac address corresponds to the multicast ip address. IANA (internet assigned number authority) stipulates that the high 24 bits of the multicast mac address are 0x01005e, and the low 23 bits of the mac address are the low 23 bits of the multicast IP address.

Since only 23 of the last 28 bits of the IP multicast address are mapped to the mac address, there will be 32 IP multicast addresses mapped to the same mac address.

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