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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 (239.255.0.0/16) 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 (239.192.0.0/14) 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 - 239.195.0.0/16

Region Scope - 239.194.0.0/16

Campus Scope - 239.193.0.0/16

I also decide to reuse the 239.193.0.0/16 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) 239.193.0.0/16 range as opposed to using the "Site-Local" 239.255.0.0/16 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 239.195.255.0/24:

For Enterprise Scope 239.195..0.0/16 the SRA space is 239.195.255.0/24

For the Region Scope 239.194.0.0/16 the SRA space is 239.194.255.0/24

For the Campus Scope 239.193.0.0/16 the SRA space is 239.193.255.0/24

For the Unused Scope 239.192.0.0/16 the SRA space is 239.192.255.0/24

Any views or practical experience out there?

1 REPLY
Silver

Re: Understanding IPv4 Multicast Administrative Scopes

The Site-Local Scope should be assigned to address range 239.255.0.0/16 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 239.192.0.0/14 or its expansion space.

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