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Appendix F. Changes from RFC 2461

This appendix summarizes the changes between RFC 4861 and its predecessor, RFC 2461.

F.1. Major Changes​

F.1.1. Updated References​

Change: References to obsolete RFCs have been updated

  • RFC 2463 (ICMPv6) → RFC 4443
  • RFC 2373 (IPv6 Addressing) → RFC 4291

F.1.2. Clarifications on Neighbor Unreachability Detection​

Change: Clarified the conditions under which Neighbor Unreachability Detection should be performed

  • Added guidance on when upper-layer reachability confirmation is sufficient
  • Clarified the relationship between DELAY and PROBE states

F.1.3. Security Considerations Enhancement​

Change: Significantly expanded Security Considerations section

  • Added detailed threat analysis
  • Discussed SEcure Neighbor Discovery (SEND)
  • Addressed new attack vectors discovered since RFC 2461

F.2. Technical Corrections​

F.2.1. Router Advertisement Processing​

Change: Clarified processing of Router Advertisements with Router Lifetime of zero

  • Such RAs are used to indicate a router is no longer available
  • Hosts must immediately remove the router from the Default Router List

F.2.2. Redirect Message Handling​

Change: Clarified that Redirect messages must only be accepted from current first-hop routers

  • Added explicit validation requirements
  • Strengthened security requirements for redirect processing

F.2.3. Prefix Information Option​

Change: Clarified handling of Prefix Information options with:

  • Preferred Lifetime > Valid Lifetime (considered invalid)
  • On-link flag and Autonomous flag interactions

F.3. Editorial Changes​

F.3.1. Terminology Consistency​

Change: Improved consistency in terminology throughout the document

  • Standardized use of "link-layer address" vs. "link-layer address"
  • Consistent use of RFC 2119 keywords (MUST, SHOULD, MAY)

F.3.2. Message Format Diagrams​

Change: Updated message format diagrams for clarity

  • Improved bit field representations
  • Added more detailed option format specifications

F.4. Behavioral Changes​

F.4.1. IsRouter Flag Handling​

Change: Clarified rules for setting and clearing the IsRouter flag

  • Specified behavior when Neighbor Advertisement with R=0 is received from a known router
  • Added requirement to remove router from Default Router List

Change: Updated to reflect current practice for link-local address generation

  • Reference to privacy extensions (RFC 4941)
  • Guidance on EUI-64 vs. alternative methods

F.4.3. Duplicate Address Detection​

Change: Minor clarifications on DAD:

  • Behavior during DAD when Neighbor Advertisement is received
  • Handling of DAD for anycast addresses

F.5. New Sections​

F.5.1. Renumbering Considerations​

Change: Added Section 12 with guidance on network renumbering

  • How to use Router Advertisements for renumbering
  • Prefix lifetime management during renumbering

F.5.2. Conceptual Sending Algorithm​

Change: Enhanced description of the conceptual sending algorithm

  • Clarified next-hop determination
  • Improved explanation of Destination Cache usage

F.6. Removed or Deprecated Content​

F.6.1. Implementation Examples​

Change: Removed some implementation-specific examples

  • Focused on protocol requirements rather than implementation choices
  • Moved implementation guidance to appendices

F.7. IANA Considerations​

Change: Updated IANA Considerations section to reflect current IANA procedures

  • Reference to RFC 8126 for registration procedures
  • Clarified option type allocation policy

F.8. Protocol Constants​

Change: Minor adjustments to protocol constant definitions

  • Clarified units and meanings
  • Added guidance on when constants can be adjusted

F.9. Impact on Implementations​

Compatibility: RFC 4861 is largely backward compatible with RFC 2461

  • Most changes are clarifications rather than functional changes
  • Security-related changes may require updates to existing implementations

Migration: Implementations can migrate incrementally

  • No flag day required for deployment
  • Interoperability maintained with RFC 2461 implementations

F.10. Summary of Key Changes​

The most significant changes from RFC 2461 are:

  1. Enhanced security guidance - Critical for modern deployments
  2. Clarified NUD behavior - Improves interoperability
  3. Updated normative references - Reflects current IPv6 specifications
  4. Renumbering considerations - Practical guidance for operators
  5. Editorial improvements - Better clarity and consistency

Note: While RFC 4861 obsoletes RFC 2461, the fundamental protocol remains the same. Most changes are clarifications, corrections, and enhancements based on implementation and deployment experience.

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