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Understanding IPv4 Multicast Administrative Scopes

I am trying to formulate our corporate policy on allocation of IP Multicast addresses. I have read RFC2365 and the Cisco "Guidelines for Enterprise IP Multicast Address Allocation" but am still a bit confused.

I understand that the "Site-Local" scope ( is the smallest scope, must be equal to or wholely contained within another scope boundary and is not sub divisible.

I also understand that the "Organization-Local" scope ( is divisible.

I am assuming that if you divide the "Org-Local" scope, the lowest level you can go to is to a /16 prefix so that it can encompass the "Site-Local" scope which is the smallest scope and must be encompassed within a boundary..

So say I choose to subdivide the "Org-Local" scope into 3:

Enterprise Scope -

Region Scope -

Campus Scope -

I also decide to reuse the scope at each campus site as non of these groups should "leak" from that site and so address reuse is possible.

Now obviously both the "Site-Local" and "Org-Local" (Campus Scope) addresses fall on a /16 boundary and meet the RFC2365 guidlines.

The confusion now arises:

When or why would I allocate an address from the "Org-Local" (Campus Scope) range as opposed to using the "Site-Local" range as they would both seem to be covered by the same administrative boundary. I am struggling to see the difference between the "Site-Local" and "Org-Local" ranges and when you use one over the other.

Also if I subdivide the "Org-Local" block into 4 /16 blocks do I end up with 4 separate "Scope Relative Address" [SRA] ranges below or do I still only have the one "Org-Local" SRA space of

For Enterprise Scope 239.195..0.0/16 the SRA space is

For the Region Scope the SRA space is

For the Campus Scope the SRA space is

For the Unused Scope the SRA space is

Any views or practical experience out there?


Re: Understanding IPv4 Multicast Administrative Scopes

The Site-Local Scope should be assigned to address range and should not be used by any other operational scopes.The address range for operational scopes (except for SSM) should be allocated from the Organization-Local group range or its expansion space.

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