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Appendix B: Changes from RFC 3513

The following changes were made from RFC 3513 "IP Version 6 Addressing Architecture":

1. Removed Restrictions on Use of IPv6 Anycast Addresses​

Removed restrictions on use of IPv6 anycast addresses because:

  • There is now sufficient experience with anycast addresses
  • These issues are not specific to IPv6
  • The GROW working group is working in this area

2. Deprecated Site-Local Unicast Prefix​

Deprecated the Site-Local unicast prefix. Changes include:

2.1 Removed Site-Local from Special Prefix List in Section 2.4​

Site-local is no longer listed as a special prefix in the address type identification table.

2.2 Split Section​

Split the section titled "Local-Use IPv6 Unicast Addresses" into two sections:

  • "Link-Local IPv6 Unicast Addresses"
  • "Site-Local IPv6 Unicast Addresses"

2.3 Added Deprecation Notice​

Added text in the new section describing the deprecation of site-local.

Reasons for deprecation:

  • Ambiguous definition of site boundaries
  • Interoperability issues with other address types
  • Replaced by Unique Local Addresses (ULA, RFC 4193)

3. Addressed Issues Raised in IAB Response to Robert Elz Appeal​

Changes made to address issues raised in the IAB response to the Robert Elz appeal include:

3.1 Address Structure Assumptions​

Added clarification in Section 2.5 stating that nodes should not make any assumptions about the structure of IPv6 addresses.

Importance: This ensures flexibility and extensibility for future address formats.

3.2 Modified EUI-64 Format​

Changed text in Section 2.5.1 and Appendix A to refer to Modified EUI-64 format interface identifiers with the "u" bit set to 1 as universal.

3.3 Interface Identifier Validation​

Added clarification in Section 2.5.1 stating that IPv6 nodes are not required to validate that interface identifiers created in the Modified EUI-64 format comply with the EUI-64 standard.

Practical significance: Simplifies implementation and improves interoperability.

4. Deprecation of IPv4-Compatible IPv6 Addresses​

4.1 Removed IPv4-Compatible Addresses​

Removed IPv4-compatible IPv6 addresses from the special prefix list in Section 2.4.

4.2 Added Deprecation Notice​

Added text in Section 2.5.5.1 stating that IPv4-compatible IPv6 addresses are deprecated.

4.3 IANA Considerations​

Added IANA Considerations in Section 4 stating that the address block containing IPv4-compatible IPv6 addresses should continue to be reserved by IETF and not reassigned for any other purpose.

Reasons for deprecation:

  • Rarely used in practice
  • Security concerns exist
  • Superseded by other IPv6 transition mechanisms

5. Other Technical Updates​

5.1 Multicast Address Flags​

Updated the definition of flags in multicast addresses, adding references to RFC 3306 (P flag) and RFC 3956 (R flag).

5.2 References Update​

Updated normative and informative references to reflect the latest relevant RFC documents.

5.3 Clarifications and Editorial Improvements​

Made various clarifications and editorial improvements to enhance the document's clarity and accuracy.

Summary of Major Changes​

Change TypeContentImpact
DeprecatedSite-local addresses (FEC0::/10)High - Should not be used in new deployments
DeprecatedIPv4-compatible addresses (::/96)Medium - Affects transition mechanisms
Removed restrictionAnycast address usage restrictionsLow - Increased flexibility
ClarificationAddress structure assumptionsLow - Improved interoperability
UpdateMulticast flag definitionsLow - Supports new features

Backward Compatibility​

The changes in this document are intended to maintain backward compatibility with RFC 3513 while:

  • Deprecating non-recommended features
  • Clarifying ambiguous specifications
  • Reflecting actual deployment experience

Recommendation: Implementations should follow this document (RFC 4291) rather than RFC 3513.

  • RFC 3513: The previous version obsoleted by this document
  • RFC 3879: Detailed description of site-local address deprecation
  • RFC 4193: Unique Local IPv6 Unicast Addresses (replacement for site-local)
  • RFC 4213: Basic Transition Mechanisms for IPv6
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