Unified Softwire CPE
draft-bfmk-softwire-unified-cpe-00

Abstract

Transporting IPv4 packets over IPv6 is a common solution to the problem of IPv4 service continuity over IPv6-only provider networks. A number of differing functional approaches have been developed for this, each having their own specific characteristics. As these approaches share a similar functional architecture and use the same data plane mechanisms, this memo describes a specification whereby a single CPE can interwork with all of the standardized and proposed approaches to providing encapsulated IPv4 in IPv6 services.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http:/⁠/⁠datatracker.ietf.org/⁠drafts/⁠current/⁠.

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This Internet-Draft will expire on June 02, 2013.

Copyright Notice

Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Rationale
• 2. Requirements Language
• 3. IPv4 Service Continuity Architectures: A 'Big Picture' Overview
• 3.1. Functional Elements
• 3.2. Required Provisoning Information
• 4. Unified Softwire CPE Behaviour
• 4.1. Full IPv4 Address Assignment
• 4.2. Customer Side NAT
• 4.3. Generic CPE Bootstrapping Logic
• 4.4. Customer Side DHCP Based Provisioning
• 4.5. Forwarding Action by the Customer End-Node
• 5. Security Considerations
• 6. IANA Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

IPv4 service continuity is one of the major technical challenges which must be considered during IPv6 migration. Over the past few years, a number of different approaches have been developed to assist with this problem. These approaches, or modes, exist in order to meet the particular deployment, scaling, addressing and other requirements of different service provider's networks. Section 3 describes these approaches in more detail.

A common feature shared between all of the differing modes is the integration of softwire tunnel end-point functionality into the CPE router. Due to this inherent data plane similarity, a single CPE may be capable of supporting several different approaches. Users may also wish to configure a specific mode of operation.

A service provider's network may also have more than one mode enabled. Reasons for this include supporting diverse CPE clients, simplifying migration between modes or where service requirements define specific supporting softwire architectures.

In order for softwire based services to be successfully established, it is essential that the customer end-node, the service provider end-node and provisioning systems are able to indicate their capabilities and preferred mode of operation.

This memo describes the logic required by both the CPE tunnel end-node and the service provider's provisioning infrastructure so that softwire services can be provided in mixed-mode environments.

1.1. Rationale

The following rationale has been adopted for this document:

(1)

Describe clear distinctions between the different solution modes

(2)

Simplify solution migration paths: Define a unified CPE behavior which allows for smooth migration between the different modes

(3)

Deterministic co-existence behavior: Specify the behavior when several modes co-exist in the CPE

(4)

Re-usability: Maximize the re-use of existing functional blocks including Tunnel Endpoint, port restricted NAPT44, Forwarding behavior, etc.

(5)

Solution agnostic: Adopt neutral terminology and avoid (as far as possible) overloading the document with solution-specific terms

(6)

Flexibility: Allow operators to compile CPE software only for the mode(s) necessary for their chosen deployment context(s)

(7)

Simplicity: Provide a model that allows operators to only implement the specific mode(s) that they require without the additional complexity of unneeded modes.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. IPv4 Service Continuity Architectures: A 'Big Picture' Overview

The solutions which have been proposed within the Softwire WG can be categorized into three main functional approaches, as listed below:

(1)

Full stateful approach (DS-Lite, [RFC6333]): Requires per-session state to be maintained in the Service Provider's network.

(2)

Binding approach (e.g., Lightweight 4over6 (Lw4o6) [I-D.cui-softwire-b4-translated-ds-lite], [I-D.ietf-softwire-public-4over6] or MAP 1:1 [I-D.ietf-softwire-map] ): Requires a single per-subscriber state (or a few) to be maintained in the Service Provider's network.

(3)

Full stateless approach (MAP, [I-D.ietf-softwire-map]): Does not require per-session or per-subscriber state to be maintained in the Service Provider's network.

All these approaches share a similar architecture, using a tunnel end-node located in a CPE and a tunnel concentrator end-node located in the service provider's network. All use IPv6 as the transport protocol for the delivery of an IPv4 connectivity service using an IPv4-in-IPv6 encapsulation scheme [RFC2473].

Throughout this document, the different techniques that have been proposed to realize these different functional approaches (DS-Lite, Lw4o6, & MAP-E) are referred to as 'modes'.

3.1. Functional Elements

Table 1 lists the required functional elements for each solution mode: