BSCI question about Multicast RFC 2365 Administratively Scoped IP Multicast

Answered Question
May 26th, 2010

Hi !

I'm currently preparing BSCI certification exam, for my studdies I read the : Authorized Self-Studdy guide BSCI.  In the chapter cover IP Multicast trafic, the author as wrote :

"

  • Limited, or administratively, scoped addresses in the range 239.0.0.0 through 239.255.255.255. As defined by Requests for Comments (RFC) 2365, Administratively Scoped IP Multicast, these addresses are reserved for use inside private domains.

"

My understanding in this text is the following : address range 239.0.0.0/8 are multicast address which will only used on private network, like it is address define by the 1918 RFC for 10.0.0.0 network as exemple.

What I"m do not understand is the following :

"The administratively scoped multicast address space includes the following scopes, per the IANA:

  • Site-local scope (239.255.0.0/16; 239.252.0.0/16, 239.253.0.0/16, and 239.254.0.0/16 are also reserved for this purpose)
  • Organization local scope (239.192.0.0 to 239.251.255.255)

The IANA has further refined these ranges, as detailed in the IANA multicast address assignment list referenced earlier."

If 239.0.0.0 is already speficied for private used, why the author wrote, the IANA as defined different range also for private used in the range already defined for private used ?

Sorry for my English, I'm a French people it's also maybe why I do not understand the explanation provide by the author here !!

Thanks a lot  !

I have this problem too.
0 votes
Correct Answer by Hitesh Vinzoda about 6 years 7 months ago

Hi,

The Reservations you are talking about are defined loosely with IPV6 context. I m showing the interesting part of the RFC

Partitioning of the Administratively Scoped Multicast Space

   The following table outlines the partitioning of the IPv4 multicast
   space, and gives the mapping from IPv4 multicast prefixes to IPv6
   SCOP values:

   IPv6 SCOP  RFC 1884 Description             IPv4 Prefix
   ===============================================================
   0          reserved
   1          node-local scope
   2          link-local scope             224.0.0.0/24
   3          (unassigned)                 239.255.0.0/16
   4          (unassigned)
   5          site-local scope
   6          (unassigned)
   7          (unassigned)
   8          organization-local scope     239.192.0.0/14
   A          (unassigned)
   B          (unassigned)
   C          (unassigned)
   D          (unassigned)
   E          global scope                 224.0.1.0-238.255.255.255
   F          reserved
              (unassigned)                 239.0.0.0/10
              (unassigned)                 239.64.0.0/10
              (unassigned)                 239.128.0.0/10

Below is the explanation

An administratively scoped IP multicast region is defined to be a
   topological region in which there are one or more boundary routers
   with common boundary definitions. Such a router is said to be a
   boundary for scoped addresses in the range defined in its
   configuration.

   Network administrators may configure a scope region whenever
   constrained multicast scope is required. In addition, an
   administrator may configure overlapping scope regions (networks can
   be in multiple scope regions) where convenient, with the only
   limitations being that a scope region must be connected (there must
   be a path between any two nodes within a scope region that doesn't
   leave that region), and convex (i.e., no path between any two points
   in the region can cross a region boundary). However, it is important
   to note that if administratively scoped areas intersect
   topologically, then the outer scope must consist of its address space
   minus the address spaces of any intersecting scopes. This requirement
   prevents the problem that would arise when a path between two points
   in a convex region crosses the boundary of an intersecting region.
   For this reason, it is recommended that administrative scopes that
   intersect topologically should not intersect in address range.

   Finally, note that any scope boundary is a boundary for the Local
   Scope. This implies that packets sent to groups covered by
   239.255.0.0/16 must not be forwarded across any link for which a
   scoped boundary is defined.

If you know the IPV6 address, you will understand it easily. Refer IPv6 multicast addressing for further clarification

HTH

Hitesh Vinzoda

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Correct Answer
Hitesh Vinzoda Tue, 06/01/2010 - 03:03

Hi,

The Reservations you are talking about are defined loosely with IPV6 context. I m showing the interesting part of the RFC

Partitioning of the Administratively Scoped Multicast Space

   The following table outlines the partitioning of the IPv4 multicast
   space, and gives the mapping from IPv4 multicast prefixes to IPv6
   SCOP values:

   IPv6 SCOP  RFC 1884 Description             IPv4 Prefix
   ===============================================================
   0          reserved
   1          node-local scope
   2          link-local scope             224.0.0.0/24
   3          (unassigned)                 239.255.0.0/16
   4          (unassigned)
   5          site-local scope
   6          (unassigned)
   7          (unassigned)
   8          organization-local scope     239.192.0.0/14
   A          (unassigned)
   B          (unassigned)
   C          (unassigned)
   D          (unassigned)
   E          global scope                 224.0.1.0-238.255.255.255
   F          reserved
              (unassigned)                 239.0.0.0/10
              (unassigned)                 239.64.0.0/10
              (unassigned)                 239.128.0.0/10

Below is the explanation

An administratively scoped IP multicast region is defined to be a
   topological region in which there are one or more boundary routers
   with common boundary definitions. Such a router is said to be a
   boundary for scoped addresses in the range defined in its
   configuration.

   Network administrators may configure a scope region whenever
   constrained multicast scope is required. In addition, an
   administrator may configure overlapping scope regions (networks can
   be in multiple scope regions) where convenient, with the only
   limitations being that a scope region must be connected (there must
   be a path between any two nodes within a scope region that doesn't
   leave that region), and convex (i.e., no path between any two points
   in the region can cross a region boundary). However, it is important
   to note that if administratively scoped areas intersect
   topologically, then the outer scope must consist of its address space
   minus the address spaces of any intersecting scopes. This requirement
   prevents the problem that would arise when a path between two points
   in a convex region crosses the boundary of an intersecting region.
   For this reason, it is recommended that administrative scopes that
   intersect topologically should not intersect in address range.

   Finally, note that any scope boundary is a boundary for the Local
   Scope. This implies that packets sent to groups covered by
   239.255.0.0/16 must not be forwarded across any link for which a
   scoped boundary is defined.

If you know the IPV6 address, you will understand it easily. Refer IPv6 multicast addressing for further clarification

HTH

Hitesh Vinzoda

Please rate useful posts

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