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.
For more related knowledge, please visit the FAQ column!
The above is the detailed content of What is the range of multicast addresses?. For more information, please follow other related articles on the PHP Chinese website!