I'm reading a little on IP multicast and have trouble understanding the significance of multicast address range ( - What makes this range significant? Why not multicast on any address?

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    Even with IPv6 that looked at improving IP, there is a specific set of addresses for multicast. IPv6 did improve multicast with scopes and flags, but it retained separate addressing because it is simple and it works. Multicast addresses cannot be assigned to interfaces or used as source addresses, so you really need a distinct range of addresses reserved for that. Unicast routing sends packets to a single host, but multicast routing is designed to prevent multicast from going where it was not requested. Multicast is network-agnostic. – Ron Maupin May 16 '20 at 22:42

Multicast ip address range is predefined in network equipment to be able to send to multiple devices at the same time ,it allows to transmit to with neither prior knowledge of a receiver's identity nor prior knowledge of the number of receivers , is use mostly in real time communication and only required the sender to send the packet one time , examples of it's use could be paging across VoIP phones . The reason why it's reserved like what @Zac67 indicated , is for the networking equipment know how to act with those addresses so it's predefined how they will treat packet with those ip's and avoid having to add additional bit's/headers of information in the packet indicating the type of communication it contains, hope it makes a litte sense

  • It makes a lot of sense. I suggest you put more effort into formatting your answers though. – Andreas May 17 '20 at 10:39

Basically, you need to draw a clear line between unicast, broadcast and multicast traffic because it needs to be treated (very) differently.

The convention is to use a special address range. Another option would have been to use header flags but that would complicate the handling in hardware. Ethernet uses a special address bit which is yet another option but costs half the address range.

In the original IP standard, addresses beginning with 111 binary were reserved. When IP multicast came along, it was allocated 1110 (class D) and 1111 (class E) remained reserved. Later still, CIDR came along and made classful addressing obsolete for unicast addresses.

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