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PROPOSED STANDARD
Errata Exist
Internet Engineering Task Force (IETF)                      T. Mrugalski
Request for Comments: 7598                                           ISC
Category: Standards Track                                       O. Troan
ISSN: 2070-1721                                            Cisco Systems
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                            S. Perreault
                                                     Jive Communications
                                                                  W. Dec
                                                           Cisco Systems
                                                                  C. Bao
                                                     Tsinghua University
                                                                  L. Yeh
                                                 Freelancer Technologies
                                                                 X. Deng
                                       The University of New South Wales
                                                               July 2015


          DHCPv6 Options for Configuration of Softwire Address
                        and Port-Mapped Clients

Abstract

   This document specifies DHCPv6 options, termed Softwire46 options,
   for the provisioning of Softwire46 Customer Edge (CE) devices.
   Softwire46 is a collective term used to refer to architectures based
   on the notion of IPv4 Address plus Port (A+P) for providing IPv4
   connectivity across an IPv6 network.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7598.








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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Conventions .....................................................3
   3. Softwire46 Overview .............................................4
   4. Common Softwire46 DHCPv6 Options ................................5
      4.1. S46 Rule Option ............................................5
      4.2. S46 BR Option ..............................................7
      4.3. S46 DMR Option .............................................8
      4.4. S46 IPv4/IPv6 Address Binding Option .......................9
      4.5. S46 Port Parameters Option ................................10
   5. Softwire46 Containers ..........................................11
      5.1. S46 MAP-E Container Option ................................11
      5.2. S46 MAP-T Container Option ................................12
      5.3. S46 Lightweight 4over6 Container Option ...................13
   6. Softwire46 Options Encapsulation ...............................14
   7. DHCPv6 Server Behavior .........................................14
   8. DHCPv6 Client Behavior .........................................14
   9. Security Considerations ........................................15
   10. IANA Considerations ...........................................16
   11. References ....................................................16
      11.1. Normative References .....................................16
      11.2. Informative References ...................................17
   Acknowledgements ..................................................18
   Authors' Addresses ................................................19











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1.  Introduction

   A number of architectural solution proposals discussed in the IETF
   Softwire Working Group use Address plus Port (A+P) [RFC6346] as their
   technology base for providing IPv4 connectivity to end users using
   Customer Edge (CE) devices across a service provider's IPv6 network,
   while allowing for shared or dedicated IPv4 addressing of CEs.

   An example is Mapping of Address and Port with Encapsulation (MAP-E)
   as defined in [RFC7597].  The MAP solution consists of one or more
   MAP Border Relay (BR) routers responsible for stateless forwarding
   between a MAP IPv6 domain and an IPv4 network, and one or more MAP
   Customer Edge (CE) routers responsible for forwarding between a
   user's IPv4 network and the MAP IPv6 network domain.  Collectively,
   the MAP CE and BR form a domain when configured with common service
   parameters.  This characteristic is common to all of the Softwire46
   mechanisms.

   To function in such a domain, a CE needs to be provisioned with the
   appropriate A+P service parameters for that domain.  These consist
   primarily of the CE's IPv4 address and transport-layer port range(s).
   Furthermore, the IPv6 transport mode (i.e., encapsulation or
   translation) needs to be specified.  Provisioning of other IPv4
   configuration information not derived directly from the A+P service
   parameters is not covered in this document.  It is expected that
   provisioning of other IPv4 configuration information will continue to
   use DHCPv4 [RFC2131].

   This memo specifies a set of DHCPv6 [RFC3315] options to provision
   Softwire46 configuration information to CE routers.  Although the
   focus is to deliver IPv4 service to an end-user network (such as a
   residential home network), it can equally be applied to an individual
   host acting as a CE.  Configuration of the BR is out of scope for
   this document.

2.  Conventions

   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].











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3.  Softwire46 Overview

   This document describes a set of common DHCPv6 options for
   configuring the Mapping of Address and Port with Encapsulation
   (MAP-E) [RFC7597], Mapping of Address and Port using Translation
   (MAP-T) [RFC7599], and Lightweight 4over6 [RFC7596] mechanisms.  For
   definitions of the terminology used in this document, please see the
   relevant terminology sections in [RFC7597], [RFC7599], and [RFC7596].

   MAP-E, MAP-T, and Lightweight 4over6 are essentially providing the
   same functionality: IPv4 service to a CE router over an IPv6-only
   access network.  MAP-E and MAP-T may embed parts of the IPv4 address
   in IPv6 prefixes, thereby supporting many clients with a fixed set of
   mapping rules and Mesh mode (direct CE-to-CE communication).  MAP-E
   and MAP-T CEs may also be provisioned in hub-and-spoke mode and in
   1:1 mode (with no embedded address bits).  The difference between
   MAP-E and MAP-T is that they use different means to connect to the
   IPv6 domain.  MAP-E uses IPv4-over-IPv6 tunneling [RFC2473], while
   MAP-T uses IPv4-to-IPv6 translation based on [RFC6145].  Lightweight
   4over6 is a hub-and-spoke IPv4-over-IPv6 tunneling mechanism, with
   complete independence of IPv4 and IPv6 addressing (zero embedded
   address bits).

   The DHCPv6 options described here tie the provisioning parameters,
   and hence the IPv4 service itself, to the End-user IPv6 prefix
   lifetime.  The validity of a Softwire46's IPv4 address, prefix, or
   shared IPv4 address; port set; and any authorization and accounting
   are tied to the lifetime of its associated End-user IPv6 prefix.

   To support more than one mechanism at a time and to allow for a
   possibility of transition between them, the DHCPv6 Option Request
   Option (ORO) [RFC3315] is used.  Each mechanism has a corresponding
   DHCPv6 container option.  A DHCPv6 client can request a particular
   mechanism by including the option code for a particular container
   option in its ORO.  The provisioning parameters for that mechanism
   are expressed by embedding the common format options within the
   respective container option.

   This approach implies that all of the provisioning options appear
   only within the container options.  Softwire46 DHCPv6 clients that
   receive provisioning options that are not encapsulated in container
   options MUST silently ignore these options.  DHCPv6 server
   administrators are advised to ensure that DHCPv6 servers are
   configured to send these options in the proper encapsulation.







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   This document is organized with the common encapsulated options
   described first (Section 4), followed by the three container options
   (Section 5).  Some encapsulated options are mandatory in some
   containers, some are optional, and some are not permitted.  This is
   shown in Table 1 (Section 6).

4.  Common Softwire46 DHCPv6 Options

   The DHCPv6 protocol is used for Softwire46 CE provisioning following
   regular DHCPv6 notions, with the CE assuming the role of a DHCPv6
   client, and the DHCPv6 server providing options following DHCPv6
   server-side policies.  The format and usage of the options are
   defined in the following subsections.

   Each CE needs to be provisioned with enough information to calculate
   its IPv4 address, IPv4 prefix, or shared IPv4 address.  MAP-E and
   MAP-T use the OPTION_S46_RULE option, while Lightweight 4over6 uses
   the OPTION_S46_V4V6BIND option.  A CE that needs to communicate
   outside of the A+P domain also needs the address or prefix of the BR.
   MAP-E and Lightweight 4over6 use the OPTION_S46_BR option to
   communicate the IPv6 address of the BR.  MAP-T forms an IPv6
   destination address by embedding an IPv4 destination address into the
   BR's IPv6 prefix conveyed via the OPTION_S46_DMR option.  Optionally,
   all mechanisms can include the OPTION_S46_PORTPARAMS option to
   specify parameters and port sets for the port-range algorithm.

   Softwire46 options use addresses rather than Fully Qualified Domain
   Names (FQDNs).  For the rationale behind this design choice, see
   Section 8 of [RFC7227].

4.1.  S46 Rule Option

   Figure 1 shows the format of the S46 Rule option (OPTION_S46_RULE)
   used for conveying the Basic Mapping Rule (BMR) and Forwarding
   Mapping Rule (FMR).

   This option follows behavior described in Sections 17.1.1 and 18.1.1
   of [RFC3315].  Clients can send those options, encapsulated in their
   respective container options, with specific values as hints for the
   server.  See Section 5 for details.  Depending on the server
   configuration and policy, it may accept or ignore the hints.  Clients
   MUST be able to process received values that are different than the
   hints it sent earlier.








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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        OPTION_S46_RULE        |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     flags     |     ea-len    |  prefix4-len  | ipv4-prefix   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  (continued)                  |  prefix6-len  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           ipv6-prefix                         |
     |                       (variable length)                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                        S46_RULE-options                       .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 1: S46 Rule Option

   o  option-code: OPTION_S46_RULE (89)

   o  option-length: length of the option, excluding option-code and
      option-length fields, including length of all encapsulated
      options; expressed in octets.

   o  flags: 8 bits long; carries flags applicable to the rule.  The
      meanings of the specific bits are explained in Figure 2.

   o  ea-len: 8 bits long; specifies the Embedded Address (EA) bit
      length.  Allowed values range from 0 to 48.

   o  prefix4-len: 8 bits long; expresses the prefix length of the
      Rule IPv4 prefix specified in the ipv4-prefix field.  Allowed
      values range from 0 to 32.

   o  ipv4-prefix: a fixed-length 32-bit field that specifies the IPv4
      prefix for the S46 rule.  The bits in the prefix after prefix4-len
      number of bits are reserved and MUST be initialized to zero by the
      sender and ignored by the receiver.

   o  prefix6-len: 8 bits long; expresses the length of the
      Rule IPv6 prefix specified in the ipv6-prefix field.  Allowed
      values range from 0 to 128.

   o  ipv6-prefix: a variable-length field that specifies the IPv6
      domain prefix for the S46 rule.  The field is padded on the right
      with zero bits up to the nearest octet boundary when prefix6-len
      is not evenly divisible by 8.



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   o  S46_RULE-options: a variable-length field that may contain zero or
      more options that specify additional parameters for this S46 rule.
      This document specifies one such option: OPTION_S46_PORTPARAMS.

   The format of the S46 Rule Flags field is:

                              0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |Reserved     |F|
                             +-+-+-+-+-+-+-+-+

                         Figure 2: S46 Rule Flags

   o  Reserved: 7 bits; reserved for future use as flags.

   o  F-flag: 1-bit field that specifies whether the rule is to be used
      for forwarding (FMR).  If set, this rule is used as an FMR; if not
      set, this rule is a BMR only and MUST NOT be used for forwarding.
      Note: A BMR can also be used as an FMR for forwarding if the
      F-flag is set.  The BMR is determined by a longest-prefix match of
      the Rule IPv6 prefix against the End-user IPv6 prefix(es).

   It is expected that in a typical mesh deployment scenario there will
   be a single BMR, which could also be designated as an FMR using the
   F-flag.

4.2.  S46 BR Option

   The S46 BR option (OPTION_S46_BR) is used to convey the IPv6 address
   of the Border Relay.  Figure 3 shows the format of the OPTION_S46_BR
   option.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         OPTION_S46_BR         |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      br-ipv6-address                          |
     |                                                               |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 3: S46 BR Option

   o  option-code: OPTION_S46_BR (90)

   o  option-length: 16



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   o  br-ipv6-address: a fixed-length field of 16 octets that specifies
      the IPv6 address for the S46 BR.

   BR redundancy can be implemented by using an anycast address for the
   BR IPv6 address.  Multiple OPTION_S46_BR options MAY be included in
   the container; this document does not further explore the use of
   multiple BR IPv6 addresses.

4.3.  S46 DMR Option

   The S46 DMR option (OPTION_S46_DMR) is used to convey values for the
   Default Mapping Rule (DMR).  Figure 4 shows the format of the
   OPTION_S46_DMR option used for conveying a DMR.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        OPTION_S46_DMR         |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |dmr-prefix6-len|            dmr-ipv6-prefix                    |
     +-+-+-+-+-+-+-+-+           (variable length)                   |
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 4: S46 DMR Option

   o  option-code: OPTION_S46_DMR (91)

   o  option-length: 1 + length of dmr-ipv6-prefix specified in octets.

   o  dmr-prefix6-len: 8 bits long; expresses the bitmask length of the
      IPv6 prefix specified in the dmr-ipv6-prefix field.  Allowed
      values range from 0 to 128.

   o  dmr-ipv6-prefix: a variable-length field specifying the IPv6
      prefix or address for the BR.  This field is right-padded with
      zeros to the nearest octet boundary when dmr-prefix6-len is not
      divisible by 8.













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4.4.  S46 IPv4/IPv6 Address Binding Option

   The S46 IPv4/IPv6 Address Binding option (OPTION_S46_V4V6BIND) MAY be
   used to specify the full or shared IPv4 address of the CE.  The IPv6
   prefix field is used by the CE to identify the correct prefix to use
   for the tunnel source.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      OPTION_S46_V4V6BIND      |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         ipv4-address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |bindprefix6-len|             bind-ipv6-prefix                  |
     +-+-+-+-+-+-+-+-+             (variable length)                 |
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                      S46_V4V6BIND-options                     .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 5: S46 IPv4/IPv6 Address Binding Option

   o  option-code: OPTION_S46_V4V6BIND (92)

   o  option-length: length of the option, excluding option-code and
      option-length fields, including length of all encapsulated
      options; expressed in octets.

   o  ipv4-address: a fixed-length field of 4 octets specifying an IPv4
      address.

   o  bindprefix6-len: 8 bits long; expresses the bitmask length of the
      IPv6 prefix specified in the bind-ipv6-prefix field.  Allowed
      values range from 0 to 128.

   o  bind-ipv6-prefix: a variable-length field specifying the IPv6
      prefix or address for the S46 CE.  This field is right-padded with
      zeros to the nearest octet boundary when bindprefix6-len is not
      divisible by 8.

   o  S46_V4V6BIND-options: a variable-length field that may contain
      zero or more options that specify additional parameters.  This
      document specifies one such option: OPTION_S46_PORTPARAMS.





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4.5.  S46 Port Parameters Option

   The S46 Port Parameters option (OPTION_S46_PORTPARAMS) specifies
   optional port set information that MAY be provided to CEs.

   See Section 5.1 of [RFC7597] for a description of the MAP algorithm
   and detailed explanation of all of the parameters.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     OPTION_S46_PORTPARAMS     |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   offset      |    PSID-len   |              PSID             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 6: S46 Port Parameters Option

   o  option-code: OPTION_S46_PORTPARAMS (93)

   o  option-length: 4

   o  offset: Port Set Identifier (PSID) offset.  8 bits long; specifies
      the numeric value for the S46 algorithm's excluded port range/
      offset bits (a-bits), as per Section 5.1 of [RFC7597].  Allowed
      values are between 0 and 15.  Default values for this field are
      specific to the softwire mechanism being implemented and are
      defined in the relevant specification document.

   o  PSID-len: 8 bits long; specifies the number of significant bits in
      the PSID field (also known as 'k').  When set to 0, the PSID field
      is to be ignored.  After the first 'a' bits, there are k bits in
      the port number representing the value of the PSID.  Consequently,
      the address-sharing ratio would be 2^k.

   o  PSID: 16 bits long.  The PSID value algorithmically identifies a
      set of ports assigned to a CE.  The first k bits on the left of
      this field contain the PSID binary value.  The remaining (16 - k)
      bits on the right are padding zeros.

   When receiving the OPTION_S46_PORTPARAMS option with an explicit
   PSID, the client MUST use this explicit PSID when configuring its
   softwire interface.  The OPTION_S46_PORTPARAMS option with an
   explicit PSID MUST be discarded if the S46 CE isn't configured with a
   full IPv4 address (e.g., IPv4 prefix).

   The OPTION_S46_PORTPARAMS option is contained within an
   OPTION_S46_RULE option or an OPTION_S46_V4V6BIND option.



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5.  Softwire46 Containers

5.1.  S46 MAP-E Container Option

   The S46 MAP-E Container option (OPTION_S46_CONT_MAPE) specifies the
   container used to group all rules and optional port parameters for a
   specified domain.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        OPTION_S46_CONT_MAPE   |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .            encapsulated-options (variable length)             .
     .                                                               .
     +---------------------------------------------------------------+

                   Figure 7: S46 MAP-E Container Option

   o  option-code: OPTION_S46_CONT_MAPE (94)

   o  option-length: length of encapsulated options, expressed in
      octets.

   o  encapsulated-options: options associated with this Softwire46
      MAP-E domain.

   The encapsulated-options field conveys options specific to the
   OPTION_S46_CONT_MAPE option.  Currently, there are two encapsulated
   options specified: OPTION_S46_RULE and OPTION_S46_BR.  There MUST be
   at least one OPTION_S46_RULE option and at least one OPTION_S46_BR
   option.

   Other options applicable to a domain may be defined in the future.  A
   DHCPv6 message MAY include multiple OPTION_S46_CONT_MAPE options
   (representing multiple domains).














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5.2.  S46 MAP-T Container Option

   The S46 MAP-T Container option (OPTION_S46_CONT_MAPT) specifies the
   container used to group all rules and optional port parameters for a
   specified domain.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     OPTION_S46_CONT_MAPT      |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .            encapsulated-options (variable length)             .
     .                                                               .
     +---------------------------------------------------------------+

                   Figure 8: S46 MAP-T Container Option

   o  option-code: OPTION_S46_CONT_MAPT (95)

   o  option-length: length of encapsulated options, expressed in
      octets.

   o  encapsulated-options: options associated with this Softwire46
      MAP-T domain.

   The encapsulated-options field conveys options specific to the
   OPTION_S46_CONT_MAPT option.  Currently, there are two options
   specified: the OPTION_S46_RULE and OPTION_S46_DMR options.  There
   MUST be at least one OPTION_S46_RULE option and exactly one
   OPTION_S46_DMR option.




















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5.3.  S46 Lightweight 4over6 Container Option

   The S46 Lightweight 4over6 Container option (OPTION_S46_CONT_LW)
   specifies the container used to group all rules and optional port
   parameters for a specified domain.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      OPTION_S46_CONT_LW       |         option-length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +            encapsulated-options (variable length)             .
     .                                                               .
     +---------------------------------------------------------------+

             Figure 9: S46 Lightweight 4over6 Container Option

   o  option-code: OPTION_S46_CONT_LW (96)

   o  option-length: length of encapsulated options, expressed in
      octets.

   o  encapsulated-options: options associated with this Softwire46
      Lightweight 4over6 domain.

   The encapsulated-options field conveys options specific to the
   OPTION_S46_CONT_LW option.  Currently, there are two options
   specified: OPTION_S46_V4V6BIND and OPTION_S46_BR.  There MUST be at
   most one OPTION_S46_V4V6BIND option and at least one OPTION_S46_BR
   option.




















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6.  Softwire46 Options Encapsulation

   The table below shows which encapsulated options are mandatory,
   optional, or not permitted for each defined container option.

      +-----------------------+-------+-------+--------------------+
      | Option                | MAP-E | MAP-T | Lightweight 4over6 |
      +-----------------------+-------+-------+--------------------+
      | OPTION_S46_RULE       |   M   |   M   |        N/P         |
      | OPTION_S46_BR         |   M   |  N/P  |         M          |
      | OPTION_S46_PORTPARAMS |   O   |   O   |         O          |
      | OPTION_S46_DMR        |  N/P  |   M   |        N/P         |
      | OPTION_S46_V4V6BIND   |  N/P  |  N/P  |         O          |
      +-----------------------+-------+-------+--------------------+

             M - Mandatory, O - Optional, N/P - Not Permitted

                  Table 1: Options for Container Mappings

   Softwire46 DHCPv6 clients that receive container options that violate
   any of the above rules MUST silently ignore such container options.

7.  DHCPv6 Server Behavior

   Section 17.2.2 of [RFC3315] describes how a DHCPv6 client and server
   negotiate configuration values using the ORO.  As a convenience for
   the reader, we mention here that by default a server will not reply
   with a Softwire46 container option if the client has not explicitly
   enumerated one in its ORO.

   A CE router may support several (or all) of the mechanisms mentioned
   here.  In the case where a client requests multiple mechanisms in its
   ORO, the server will reply with the corresponding Softwire46
   container options for which it has configuration information.

8.  DHCPv6 Client Behavior

   An S46 CE acting as a DHCPv6 client will request S46 configuration
   parameters from the DHCPv6 server located in the IPv6 network.  Such
   a client MUST request the S46 container option(s) that it is
   configured for in its ORO in SOLICIT, REQUEST, RENEW, REBIND, and
   INFORMATION-REQUEST messages.









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   When processing received S46 container options, the following
   behavior is expected:

   o  A client MUST support processing multiple received OPTION_S46_RULE
      options in a container OPTION_S46_CONT_MAPE or
      OPTION_S46_CONT_MAPT option.

   o  A client receiving an unsupported S46 option or an invalid
      parameter value SHOULD discard that S46 container option and log
      the event.

   The behavior of a client that supports multiple Softwire46 mechanisms
   is out of scope for this document.  [Unified-v4-in-v6] describes
   client behavior for the prioritization and handling of multiple
   mechanisms simultaneously.

   Note that a system implementing CE functionality may have multiple
   network interfaces, and these interfaces may be configured
   differently; some may be connected to networks using a Softwire46
   mechanism, and some may be connected to networks that are using
   normal dual-stack or other means.  The CE should approach this
   specification on an interface-by-interface basis.  For example, if
   the CE system is MAP-E capable and is attached to multiple networks
   that provide the OPTION_S46_CONT_MAPE option, then the CE MUST
   configure MAP-E for each interface separately.

   Failure modes are out of scope for this document.  Failure recovery
   mechanisms may be defined in the future.  See Section 5 of [RFC7597]
   for a discussion of valid MAP Rule combinations.  See Section 11 of
   [RFC7227] and Sections 18.1.3, 18.1.4, and 19.1 of [RFC3315] for
   parameter-update mechanisms in DHCPv6 that can be leveraged to update
   configuration after a failure.

9.  Security Considerations

   Section 23 of [RFC3315] discusses DHCPv6-related security issues.

   As with all DHCPv6-derived configuration states, it is possible that
   configuration is actually being delivered by a third party (Man in
   the Middle).  As such, there is no basis on which access over MAP or
   Lightweight 4over6 can be trusted.  Therefore, softwires should not
   bypass any security mechanisms such as IP firewalls.

   In IPv6-only networks that lack IPv4 firewalls, a device that
   supports MAP could be tricked into enabling its IPv4 stack and
   directing IPv4 traffic to the attacker, thus exposing itself to
   previously infeasible IPv4 attack vectors.




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   Section 10 of [RFC7597] discusses security issues related to the
   MAP-E mechanism, Section 9 of [RFC7596] discusses security issues
   related to the Lightweight 4over6 mechanism, and Section 13 of
   [RFC7599] discusses security issues related to the MAP-T mechanism.

   Readers concerned with the security of Softwire46 provisioning over
   DHCPv6 are encouraged to read [Secure-DHCPv6].

10.  IANA Considerations

   IANA has allocated the following DHCPv6 option codes:

      89 for OPTION_S46_RULE

      90 for OPTION_S46_BR

      91 for OPTION_S46_DMR

      92 for OPTION_S46_V4V6BIND

      93 for OPTION_S46_PORTPARAMS

      94 for OPTION_S46_CONT_MAPE

      95 for OPTION_S46_CONT_MAPT

      96 for OPTION_S46_CONT_LW

   All values have been added to the "Dynamic Host Configuration
   Protocol for IPv6 (DHCPv6)" option code space defined in Section 24.3
   of [RFC3315].

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315,
              July 2003, <http://www.rfc-editor.org/info/rfc3315>.






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11.2.  Informative References

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <http://www.rfc-editor.org/info/rfc2131>.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <http://www.rfc-editor.org/info/rfc2473>.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
              <http://www.rfc-editor.org/info/rfc6145>.

   [RFC6346]  Bush, R., Ed., "The Address plus Port (A+P) Approach to
              the IPv4 Address Shortage", RFC 6346,
              DOI 10.17487/RFC6346, August 2011,
              <http://www.rfc-editor.org/info/rfc6346>.

   [RFC7227]  Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
              S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
              BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
              <http://www.rfc-editor.org/info/rfc7227>.

   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and
              I. Farrer, "Lightweight 4over6: An Extension to the
              Dual-Stack Lite Architecture", RFC 7596,
              DOI 10.17487/RFC7596, July 2015,
              <http://www.rfc-editor.org/info/rfc7596>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <http://www.rfc-editor.org/info/rfc7597>.

   [RFC7599]  Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
              and T. Murakami, "Mapping of Address and Port using
              Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599,
              July 2015, <http://www.rfc-editor.org/info/rfc7599>.











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   [Secure-DHCPv6]
              Jiang, S., Ed., Shen, S., Zhang, D., and T. Jinmei,
              "Secure DHCPv6", Work in Progress,
              draft-ietf-dhc-sedhcpv6-08, June 2015.

   [Unified-v4-in-v6]
              Boucadair, M., Farrer, I., Perreault, S., Ed., and S.
              Sivakumar, Ed., "Unified IPv4-in-IPv6 Softwire CPE", Work
              in Progress, draft-ietf-softwire-unified-cpe-01, May 2013.

Acknowledgements

   This document was created as a product of a MAP design team.  The
   following people were members of that team: Congxiao Bao, Mohamed
   Boucadair, Gang Chen, Maoke Chen, Wojciech Dec, Xiaohong Deng, Jouni
   Korhonen, Xing Li, Satoru Matsushima, Tomek Mrugalski, Tetsuya
   Murakami, Jacni Qin, Necj Scoberne, Qiong Sun, Tina Tsou, Dan Wing,
   Leaf Yeh, and Jan Zorz.

   The authors would like to thank Bernie Volz and Tom Taylor for their
   insightful comments and suggestions.






























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Authors' Addresses

   Tomek Mrugalski
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City, CA  94063
   United States

   Phone: +1 650 423 1345
   Email: tomasz.mrugalski@gmail.com
   URI:   http://www.isc.org/


   Ole Troan
   Cisco Systems
   Philip Pedersens vei 1
   Lysaker  1366
   Norway

   Email: ot@cisco.com


   Ian Farrer
   Deutsche Telekom AG
   CTO-ATI, Landgrabenweg 151
   Bonn, NRW  53227
   Germany

   Email: ian.farrer@telekom.de


   Simon Perreault
   Jive Communications
   Quebec, QC
   Canada

   Email: sperreault@jive.com


   Wojciech Dec
   Cisco Systems, Inc.
   The Netherlands

   Email: wdec@cisco.com
   URI:   http://cisco.com






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   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   China

   Phone: +86 10-62785983
   Email: congxiao@cernet.edu.cn


   Leaf Y. Yeh
   Freelancer Technologies
   China

   Email: leaf.y.yeh@hotmail.com


   Xiaohong Deng
   The University of New South Wales
   Sydney  NSW 2052
   Australia

   Email: dxhbupt@gmail.com
   URI:   https://www.unsw.edu.au/



























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