Routing Aspects of IPv6 Transition
RFC 2185

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Network Working Group                                          R. Callon
Request for Comments: 2185                    Cascade Communications Co.
Category: Informational                                        D. Haskin
                                                       Bay Networks Inc.
                                                          September 1997

                   Routing Aspects Of IPv6 Transition

Status of this memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This document gives an overview of the routing aspects of the IPv6
   transition.  It is based on the protocols defined in the document
   "Transition Mechanisms for IPv6 Hosts and Routers" [1].  Readers
   should be familiar with the transition mechanisms before reading this
   document.

   The proposals contained in this document are based on the work of the
   Ngtrans working group.

1. TERMINOLOGY

   This paper uses the following terminology:

   node      - a protocol module that implements IPv4 or IPv6.

   router    - a node that forwards packets not explicitly
               addressed to itself.

   host      - any node that is not a router.

   border router - a router that forwards packets across
               routing domain boundaries.

   link      - a communication facility or medium over which
               nodes can communicate at the link layer, i.e., the layer
               immediately below internet layer.

   interface - a node's attachment to a link.

   address   - an network layer identifier for an interface or
               a group of interfaces.

Callon & Haskin              Informational                      [Page 1]
RFC 2185           Routing Aspects Of IPv6 Transition     September 1997

   neighbors - nodes attached to the same link.

   routing domain - a collection of routers which coordinate
               routing knowledge using a single routing protocol.

   routing region (or just "region")  - a collection of routers
               interconnected by a single internet protocol (e.g. IPv6)
               and coordinating their routing knowledge using routing
               protocols from a single internet protocol stack. A
               routing region may be a superset of a routing domain.

   tunneling  - encapsulation of protocol A within protocol B,
               such that A treats B as though it were a datalink layer.

   reachability information - information describing the set of
               reachable destinations that can be used for packet
               forwarding decisions.

   routing information - same as reachability information.

   address prefix - the high-order bits in an address.

   routing prefix - address prefix that expresses destinations
               which have addresses with the matching address prefixes.
               It is used by routers to advertise what systems they are
               capable of reaching.

   route leaking - advertisement of network layer reachability
               information across routing region boundaries.

2. ISSUES AND OUTLINE

   This document gives an overview of the routing aspects of IPv4 to
   IPv6 transition. The approach outlined here is designed to be
   compatible with the existing mechanisms for IPv6 transition [1].

   During an extended IPv4-to-IPv6 transition period, IPv6-based systems
   must coexist with the installed base of IPv4 systems. In such a dual
   internetworking protocol environment, both IPv4 and IPv6 routing
   infrastructure will be present. Initially, deployed IPv6-capable
   domains might not be globally interconnected via IPv6-capable
   internet infrastructure and therefore may need to communicate across
   IPv4-only routing regions. In order to achieve dynamic routing in
   such a mixed environment, there need to be mechanisms to globally
   distribute IPv6 network layer reachability information between
   dispersed IPv6 routing regions. The same techniques can be used in
   later stages of IPv4-to-IPv6 transition to route IPv4 packets between
   isolated IPv4-only routing region over IPv6 infrastructure.

Callon & Haskin              Informational                      [Page 2]
RFC 2185           Routing Aspects Of IPv6 Transition     September 1997

   The IPng transition provides a dual-IP-layer transition, augmented by
   use of encapsulation where necessary and appropriate. Routing issues
   related to this transition include:

   (1) Routing for IPv4 packets

   (2) Routing for IPv6 packets
           (2a) IPv6 packets with IPv6-native addresses
           (2b) IPv6 packets with IPv4-compatible addresses

   (3) Operation of manually configured static tunnels

   (4) Operation of automatic encapsulation
           (4a) Locating encapsulators
           (4b) Ensuring that routing is consist with
               encapsulation

   Basic mechanisms required to accomplish these goals include: (i)