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What is the difference between Node-Local-Scope, Site-Local-Scope and Link-Local-Scope ?

What does it mean Link local (link only) ? Is it only for a Subnet ? Why do we need site-local address then ?

Thanks in Advance Sajith

  • Are you referring to IPv6 multicast? – Ron Maupin Jan 26 '18 at 23:08
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For unicast IPv6, you don't have scopes the way you have in your question. There are Reserved unicast addresses, Global unicast addresses (2000::/3'), Unique-Local unicast addresses (fc00::/7, with restrictions), and Link-Local unicast addresses (fe80::/10).

IPv6 Link-Local unicast has identifiers to uniquely identify the interface in a host that are often called the scope (or zone) identifier. This is necessary because all the interfaces will use the same network. See the IANA IPv6 Special-Purpose Address Registry. The IPv6 unicast Link-Local addressing is only valid on the link because every link has the same network, and you cannot route or send traffic from one link to another using Link-Local addresses.

IPv6 multicast that has:

  • Interface-Local scope
  • Link-Local scope
  • Realm-Local scope
  • Admin-Local scope
  • Site-Local scope
  • Organization-Local scope
  • Global scope

RFC 4291, IP Version 6 Addressing Architecture, Section 2.7. Multicast Addresses defines some of these:

Interface-Local scope spans only a single interface on a node and is useful only for loopback transmission of multicast.

Link-Local multicast scope spans the same topological region as the corresponding unicast scope.

Admin-Local scope is the smallest scope that must be administratively configured, i.e., not automatically derived from physical connectivity or other, non-multicast-related configuration.

Site-Local scope is intended to span a single site.

Organization-Local scope is intended to span multiple sites belonging to a single organization.

RFC 7346, IPv6 Multicast Address Scopes updates the IPv6 multicast scopes:

  1. Definition of IPv6 Multicast Address Scopes (Updates RFC 4291)

    The following table updates the definitions in [RFC4291]:

    +------+--------------------------+-------------------------+
    | scop | NAME                     | REFERENCE               |
    +------+--------------------------+-------------------------+
    |  0   | Reserved                 | [RFC4291], RFC 7346     |
    |  1   | Interface-Local scope    | [RFC4291], RFC 7346     |
    |  2   | Link-Local scope         | [RFC4291], RFC 7346     |
    |  3   | Realm-Local scope        | [RFC4291], RFC 7346     |
    |  4   | Admin-Local scope        | [RFC4291], RFC 7346     |
    |  5   | Site-Local scope         | [RFC4291], RFC 7346     |
    |  6   | Unassigned               |                         |
    |  7   | Unassigned               |                         |
    |  8   | Organization-Local scope | [RFC4291], RFC 7346     |
    |  9   | Unassigned               |                         |
    |  A   | Unassigned               |                         |
    |  B   | Unassigned               |                         |
    |  C   | Unassigned               |                         |
    |  D   | Unassigned               |                         |
    |  E   | Global scope             | [RFC4291], RFC 7346     |
    |  F   | Reserved                 | [RFC4291], RFC 7346     |
    +------+--------------------------+-------------------------+
    

The following change is applied to Section 2.7 of [RFC4291].

OLD:

Admin-Local scope is the smallest scope that must be administratively configured, i.e., not automatically derived from physical connectivity or other, non-multicast-related configuration.

NEW:

Interface-Local, Link-Local, and Realm-Local scope boundaries are automatically derived from physical connectivity or other non- multicast-related configurations. Global scope has no boundary. The boundaries of all other non-reserved scopes of Admin-Local or larger are administratively configured. For reserved scopes, the way of configuring their boundaries will be defined when the semantics of the scope are defined.

According to RFC 4007 [RFC4007], the zone of a Realm-Local scope must fall within zones of larger scope. Because the zone of a Realm-Local scope is configured automatically while the zones of larger scopes are configured manually, care must be taken in the definition of those larger scopes to ensure that the inclusion constraint is met.

Realm-Local scopes created by different network technologies are considered to be independent and will have different zone indices (see Section 6 of [RFC4007]). A router with interfaces on links using different network technologies does not forward traffic between the Realm-Local multicast scopes defined by those technologies.

  1. Definition of Realm-Local Scopes

The definition of any Realm-Local scope for a particular network technology should be published in an RFC. For example, such a scope definition would be appropriate for publication in an "IPv6-over-foo" RFC.

Any RFCs that include the definition of a Realm-Local scope will be added to the IANA "IPv6 Multicast Address Scopes" registry under the Realm-Local scope entry, and those specifications must include such a request in their IANA Considerations.

Section 5 of this document gives the definition of scop 3 for IEEE 802.15.4 [IEEE802.15.4] networks.

  1. Definition of Automatic and Administratively Configured Scopes (Updates RFC 4007)

Section 5 of RFC 4007 [RFC4007] and Section 2.7 of RFC 4291 [RFC4291] disagree on the way in which multicast scop 3 is configured. To resolve that disagreement, the last bullet in the list in Section 5 of [RFC4007] is updated as follows:

OLD:

o The boundaries of zones of a scope other than interface-local, link-local, and global must be defined and configured by network administrators.

NEW:

o The boundaries of zones of a scope are defined by the IPv6 addressing architecture [RFC4291] and updated by RFC 7346.

  1. Definition of Realm-Local Scope for IEEE 802.15.4

When used in an IP-over-IEEE802.15.4 network, scop 3 is defined to include all interfaces sharing a Personal Area Network Identifier (PAN ID).

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