Attribute-Value Pairs For Provisioning Customer Equipment Supporting IPv4-Over-IPv6 Transitional Solutions
draft-zhou-dime-4over6-provisioning-00

Abstract

During the transition from IPv4 to IPv6, customer equipment may have to support one of the various transition methods that have been or are currently being defined for carrying IPv4 packets over IPv6. Work is currently in progress to enumerate the information that needs to be provisioned on a customer edge router to support a list of transition techniques based on tunneling IPv4 in IPv6, with a view to defining reusable components for a reasonable transition path between these techniques. To the extent that the provisioning is done dynamically, AAA support is needed to provide the information to the network server responsible for passing the information to the customer equipment. This document specifies Diameter attribute-value pairs to be used for that purpose.

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 October 13, 2013.

Copyright Notice

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Description of the Parameters Required By Each Transition Method
• 2.1. Parameters For Dual-Stack Lite
• 2.2. Public IPv4 Over IPv6
• 2.3. Light Weight IPv4 Over IPv6 (LW4o6)
• 2.4. Mapping of Address and Port with Encapsulation (MAP-E)
• 2.5. Summing Up
• 3. Attribute-Value Pair Definitions
• 3.1. Border Router IPv6 Address
• 3.2. IPv4 Prefix or Address
• 3.3. IPv6 Prefix or Address
• 3.4. Port Set Identifier
• 3.5. Transition Method Indicator
• 3.6. NAT Pool Identifier
• 3.7. Binding Between An IPv4 Address and IPv6 Address/Prefix Assigned to a Customer Edge Device
• 3.8. MAP Rule AVP
• 4. Acknowledgements
• 5. IANA Considerations
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

A number of transition technologies have been or are being defined to allow IPv4 packets to pass between hosts and IPv4 networks over an intervening IPv6 network while minimizing the number of public IPv4 addresses that need to be consumed by the hosts. Different operators will deploy different technologies, and sometimes one operator will use more than one technology, depending on what is supported by the available equipment and upon other factors both technical and economic.

Each technique requires the provisioning of some subscriber- specific information on the customer edge device. The provisioning may be by DHCP or by some other method. This document is indifferent to the specific provisioning technique used, but assumes that the information originates in the AAA infrastructure. To allow the information to be carried in Diameter [RFC6733], this document specifies a number of attribute-value pairs (AVPs) for the purpose.

This document takes as its scope the set of transition methods provided for by [I_D.softwire-unified-cpe]. That document enumerates the information that must be provisioned in the customer edge router to support Dual-Stack Lite [RFC6333], Public IPv4 Over IPv6 [I-D.ietf-softwire-public-4over6], Light Weight IPv4 Over IPv6 (LW4o6) [I-D.cui-softwire-b4-translated-ds-lite], and Mapping of Address and Port with Encapsulation (MAP-E) [I-D.ietf-softwire-map].

Several documents provide related specifications for RADIUS [RFC2865], for individual transition methods. Potentially there could be a reconciliation between the contents of those documents and the present one, but that has not been done in the present version of this document.

1.1. 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 RFC 2119 [RFC2119].

2. Description of the Parameters Required By Each Transition Method

This section reviews the parameters that need to be provisioned for each of the transition methods listed above. This enumeration provides the justification for the AVPs defined in the next section. Since most of the transition methods dealt with here are works in progress, this section is subject to modification in future versions.

2.1. Parameters For Dual-Stack Lite

Dual-Stack Lite is documented in [RFC6333]. It requires the following parameters to be provisioned at the B4 at the customer premises. This enumeration does not include the normal provisioning of an IPv6 prefix to the customer equipment. The section numbers shown are where these requirements are indicated in [RFC6333].

• IPv6 address of the border router (AFTR) (sec. 5.4);
• IPv6 address of a DNS recursive server (sec. 5.5). This is probably supplied already independently of transition technology, so does not have to be covered here.
• an indicator that DS-Lite is to be used rather than some other transition method (sec. 5.6). Note that [RFC6333] says that the choice should be made by unspecified means during initialization, while [I_D.softwire-unified-cpe] specifies how to infer the intended method from other DHCP parameters received. Thus the indicator suggested here may not come from AAA.
• optionally, the IPv4 address of the B4 interface facing the tunnel, where the default value in the absence of provisioning is 192.0.0.2 and valid values are 192.0.0.2 through 192.0.0.7 (sec. 5.7).

The AFTR may also require an item of per-subscriber information (sec. 8.1):

• the identity of the NAT pool to which the subscriber is to be assigned.

2.2. Public IPv4 Over IPv6

Public IPv4 Over IPv6 is described in [I-D.ietf-softwire-public-4over6]. Besides the usual IPv6 prefix or address information, it requires two parameters to be provisioned to the customer equipment:

• a public IPv4 address;
• IPv6 address of the border router

It also requires per-subscriber provisioning on the border router:

• binding between the customer IPv4 address and the customer IPv6 prefix, for routing of incoming packets to the correct tunnel.

2.3. Light Weight IPv4 Over IPv6 (LW4o6)

Light Weight IPv4 Over IPv6 (LW4o6) is documented in [I-D.cui-softwire-b4-translated-ds-lite]. Its provisioning requirements are exactly the same as those for Public 4over6 with one addition:

• both the customer equipment and the border router are provided with a port set identifier identifying the set of ports to which the subscriber's incoming and outgoing packets on the public side are restricted. The port selection algorithm and port set identifier as such are not discussed in the draft. For the present version of this document, it is assumed that the algorithm is known in advance and the port set identifier has the form of an index ranging from zero to the number of subscribers sharing a given address less 1. This is similar to the port set identifier in MAP-E, described next.

2.4. Mapping of Address and Port with Encapsulation (MAP-E)

Mapping of Address and Port with Encapsulation (MAP-E) is described in [I-D.ietf-softwire-map]. MAP-E requires the provisioning of the following per-subscriber information at the customer edge device:

• whether the device is to operate in mesh or hub-and-spoke mode;
• the IPv6 address of the border router, also known as the Default Mapping rule;
• the specially constructed End-user IPv6 prefix for the customer edge device. [I-D.ietf-softwire-map] suggests that this would be supplied as part of normal IPv6 provisioning, so it can be ignored as a requirement here.
• the Basic Mapping Rule for the customer edge device. This includes the following parameters:
  • the rule IPv6 prefix and length;
  • the rule IPv4 prefix and length;
  • the number of "Extended Address" (EA) bits included in the End-user IPv6 prefix;
  • of those Extended Address bits, the number that precede the port set identifier. This is currently a matter of discussion, whether it should default to 4 or 6 or be fixed at either of these values.

• in mesh mode only, zero or more Forwarding Mapping Rules, containing the same parameters as the Basic Mapping rule.
• optionally, the port set identifier if the EA bits do carry it.

The border router needs to be configured with the superset of the Forwarding MAP Rules passed to the customer sites it serves. Since this is not subscriber-specific, even though it introduces no new requirements to this document, it is out of scope.

2.5. Summing Up

It appears that the following items are common to two or more methods and should therefore be specified in method-independent fashion:

• the IPv6 address of the border router;
• an IPv4 prefix and length (could be a /32);
• a port set identifier;
• tentatively, a method indicator, indicating which of the above transition methods the customer edge device must use.

The remaining requirements are method-specific:

• for DS-Lite, the identity of the NAT pool to which the subscriber is assigned;
• for Public 4over6 and LW4o6, a binding between a customer IPv6 prefix or address and an IPv4 address;
• for MAP-E, the indication of whether mesh mode or hub-and-spoke mode is to be used;
• for MAP-E, a Grouped AVP expressing a MAP Rule.

3. Attribute-Value Pair Definitions

This section provides the specifications for the AVPs needed to meet the requirements summarized in Section 2.5. Within the context of their usage, all of these AVPs MUST have the M bit set and the V bit cleared.

3.1. Border Router IPv6 Address

The Border-Router-IPv6-Address (AVP Code TBD01) is of type Address as defined in Section 4.3 of [RFC6733] and contains the IPv6 address of a border router supporting an IPv6 transition method which will be used by the customer edge device on which this address is provisioned. The address MAY be an anycast address. Since the content is an IPv6 address, the AVP Length MUST be set to 26 and the first two octets MUST contain 0x0002 (IPv6).

3.2. IPv4 Prefix or Address

The IPv4-Prefix-Or-Addr (AVP Code TBD02) is derived from base type OctetString. It is a discriminated union representing the combination of the prefix length (number of bits) in the first octet, followed by the prefix itself, most significant octet first, padded with zeroes at the low-order end to an octet boundary. Valid values of the prefix length are from 0 to 32, where 0 indicates that the prefix is absent and 32 indicates a complete address. Correspondingly, the AVP Length can range from 9 to 13.

3.3. IPv6 Prefix or Address

The IPv6-Prefix-Or-Addr (AVP Code TBD03) is derived from base type OctetString. It is a discriminated union representing the combination of the prefix length (number of bits) in the first octet, followed by the prefix itself, most significant octet first, padded with zeroes at the low-order end to an octet boundary. Valid values of the prefix length are from 0 to 128, where 0 indicates that the prefix is absent and 128 indicates a complete address. Correspondingly, the AVP Length can range from 9 to 25.

3.4. Port Set Identifier

The Port-Set-Identifier AVP (AVP Code TBD04) is of type Unsigned32 and indicates a set of ports defined by an otherwise-specified algorithm. For a given shared address, each Port-Set-Identifier value MUST identify a separate set of ports. AVP Length for the Port-Set-Identifier AVP MUST be set to 12.

3.5. Transition Method Indicator

The Transition-Method AVP (AVP Code TBD05) is of type Enumerated and indicates the IPv6 transition method to be used. This document specifies the following values:

• 0 NO_METHOD
• 1 DUAL_STACK
• 2 DS_LITE
• 3 PUBLIC_4OVER6
• 4 LIGHT_WEIGHT_4OVER6
• 5 MAP_WITH_ENCAPSULATION

NO_METHOD indicates that the network will not support any transition method, and expects only IPv6 packets. DUAL_STACK indicates that the network will accept either IPv4 or IPv6 packets. [Maybe references should be added for the other values?]

The AVP Length for the Transition-Method AVP MUST be set to 12.

3.6. NAT Pool Identifier

NAT-Poolid (AVP Code TBD06) is of type Unsigned32 and indicates the NAT pool on a network-based NAT to which a subscriber is to be assigned. The set of valid values for this AVP is a local matter. The AVP Length for the NAT-Poolid AVP MUST be set to 12.

3.7. Binding Between An IPv4 Address and IPv6 Address/Prefix Assigned to a Customer Edge Device

4to6-Binding (AVP Code TBD07) is of type Grouped. It provides an IPv4 address or prefix assigned to a customer edge device, a corresponding IPv6 address or prefix assigned to the tunnel interface at the customer edge device, and, if the IPv4 address is shared, a port set identifier indicating the valid set of ports for this customer edge device. The contents of the 4to6-Binding AVP are required at the border router when Public 4over6 or Light-Weight 4over6 is being used.

If the port set identifier is present, the IPv4 address MUST be a full IPv4 address. The port set identifier is relevant only if Light-Weight 4over6 is being used.

The syntax of the 4to6-Binding AVP is given as follows, where the component AVPs were defined above. The final *[ AVP ] component is added for extensibility.

         4to6-Binding  ::= < AVP Header: TBD07 >
                          { IPv4-Prefix-Or-Addr }
                          { IPv6-Prefix-Or-Addr }
                       0*1{ Port-Set-Identifier }
                         *[ AVP ]
          

         MAP-Rule      ::= < AVP Header: TBD08 >
                          { IPv4-Prefix-Or-Addr }
                          { IPv6-Prefix-Or-Addr }
                          { EA-Field-Length     }
                          [ PSID-Offset         ]
                         *[ AVP ]