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Whats the difference between:

Local subnetwork

Addresses in the range 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 & 224.0.0.6, and Zeroconf mDNS uses 224.0.0.251. Routers must not forward these messages outside the subnet in which they originate.

and

Administratively Scoped IPv4 Multicast addresses

The 239.0.0.0/8 range is assigned by RFC 2365 for private use within an organization. From the RFC, packets destined to administratively scoped IPv4 multicast addresses do not cross administratively defined organizational boundaries, and administratively scoped IPv4 multicast addresses are locally assigned and do not have to be globally unique. The RFC also discusses structuring the 239.0.0.0/8 range to be loosely similar to the scoped IPv6 multicast address range described in RFC 1884.

Am i right that if you use the 224 block you have to adapt to the guides that are described in the RFC to the IANA reserved addresses while on the 239 block you can do what you want?

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Gobliins
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1 Answers1

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I agree with you. I read this as 224.0.0.0 - 224.0.0.255 are assigned by IANA, so unless they assigned the address you are trying to use you shouldn't use them. Which also means that you should only use 224.0.0.251 for mDNS (as described by the relevant document), and you should not use anything that is not currently in use, as it may get assigned later on.

239.0.0.0/8 - sounds like the equivalent of 10.0.0.0/8 for multicast. Just make sure you don't route 239.0.0.0/8 multicasts to a network that is not under your control. Which is also the case for the private IPv4 addresses but in practice this is not the case.

chutz
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