Softwire                                                    T. Mrugalski
Internet-Draft                                                       ISC
Intended status: Standards Track                                   P. Wu
Expires: October 8, 2012                             Tsinghua University
                                                           April 6, 2012

Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for DHCPv4
                          over IPv6 Transport


   [I-D.ietf-dhc-dhcpv4-over-ipv6] defines a way for communication
   between legacy DHCPv4 clients with DHCPv4 servers over IPv6-only
   transport.  It requires the deployment of Client Relay Agent (CRA)
   that transmits messages to IPv6-Transport Server (TSV) or IPv6-
   Transport Relay Agent (TRA).  The deployed CRA must know the address
   of a TSV or TRA to forward incoming client's messages.  This document
   defines an DHCPv6 option that may be used to provision the TSV or TRA
   location to CRAs.

Status of this Memo

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

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   This Internet-Draft will expire on October 8, 2012.

Copyright Notice

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   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.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  The DHCPv4-Over-IPv6 DHCPv6 Option  . . . . . . . . . . . . . . 3
   4.  DHCPv6 Server Behavior  . . . . . . . . . . . . . . . . . . . . 5
   5.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Introduction

   [I-D.ietf-dhc-dhcpv4-over-ipv6] defines a way for communication
   between legacy DHCPv4 clients with DHCPv4 servers (defined in
   [RFC2131]) over IPv6-only transport.  It requires the deployment of
   Client Relay Agent (CRA) that transmits messages to IPv6-Transport
   Server (TSV) or IPv6-Transport Relay Agent (TRA).  There are several
   scenarios envisaged, all of them assume that CRA needs to know the
   recipient address of the DHCPv4-over-IPv6 traffic.

   Depending on the scenario discussed, the DHCPv4 over IPv6 transport
   endpoint could be either an IPv6-Transport Server (TSV) or an IPv6-
   Transport Relay Agent (TRA).  Both cases are indistinguishable from
   the CRA's perspective.  CRA needs to know TSV's or TRA's IPv6 address
   in advance to relay traffic.

   As the CRA uplink is IPv6-only (otherwise there would be no need to
   deploy DHCPv4 over IPv6), the only feasible way to provision
   information to CRA is over DHCPv6.  Therefore this document specifies
   a DHCPv6 option that conveys the necessary information to CRA.  To be
   more specific, a single DHCPv6 [RFC3315] option is used, expressing
   the TRA's or TSV's Fully Qualified Domain Name (FQDN) to the CRA.

3.  The DHCPv4-Over-IPv6 DHCPv6 Option

   The DHCPv4-over-IPv6 option is a DHCPv6 option.  It consists of an
   option-code and option-len fields (as all DHCPv6 options have), and a
   variable length dhcpv4-over-ipv6-endpoint-name field containing a
   fully qualified domain name that refers to the DHCPv4 over IPv6
   transport endpoint to which the CRA MAY transport DHCPv4 traffic.
   This name represents a TRA or TSV, depending on deployment scenario.

   The DHCPv4-over-IPv6 option SHOULD NOT appear in any other than the
   following DHCPv6 messages: Solicit, Advertise, Request, Renew,
   Rebind, Information-Request and Reply.

   The format of the DHCPv4 over IPv6 option is shown in the following

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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_DHCP4_OVER_V6: (TBD)   |          option-len           |
    |                                                               |
    |              dhcpv4-over-ipv6-endpoint-name (FQDN)            |
    |                                                               |


               option-len: Length of the dhcpv4-over-ipv6-endpoint-name
                           field, expressed in octets.

      dhcpv4-over-ipv6-endpoint-name: A fully qualified domain name
                         of the DHCPv4-over-IPv6 transport endpoint.

                 Figure 1: AFTR-Name DHCPv6 Option Format

   The dhcpv4-over-ipv6-endpoint-name field is formatted as required in
   DHCPv6 [RFC3315] Section 8 ("Representation and Use of Domain
   Names").  Briefly, the format described uses a single octet noting
   the length of one DNS label (limited to at most 63 octets), followed
   by the label contents.  This repeats until all labels in the FQDN are
   exhausted, including a terminating zero-length label.  Any updates to
   Section 8 of DHCPv6 [RFC3315] also apply to encoding of this field.
   An example format for this option is shown in Figure 2, which conveys
   the FQDN "".
      | 0x04 |   d  |   h  |   c  |   p  | 0x07 |   e  |   x  |   a  |
      |   m  |   p  |   l  |   e  | 0x03 |   c  |   o  |   m  | 0x00 |

             Figure 2: Example dhcpv4-over-ipv6-endpoint-name.

   Note that in the specific case of the example (Figure 2), the length
   of the dhcpv4-over-ipv6-endpoint-name is 18 octets, and so an option-
   len field value of 18 would be used.

   The option is validated by confirming that all of the following
   conditions are met:

   1.  the option-len is greater than 3;

   2.  the option data can be contained by the option length, and the
       option length does not run off the end of the packet;

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   3.  the individual label lengths do not exceed the option length;

   4.  the dhcpv4-over-ipv6-endpoint-name is of valid format as
       described in DHCPv6 Section 8 [RFC3315];

   5.  there are no compression tags;

   6.  there is at least one label of nonzero length.

4.  DHCPv6 Server Behavior

   A DHCPv6 server SHOULD NOT send more than one DHCPv4-over-IPv6
   option.  It SHOULD NOT permit the configuration of multiple names
   within one DHCPv4-over-IPv6 option.  Both of these conditions are
   handled as exception by the client, so an operator using software
   that does not perform these validations should be careful not to
   configure multiple domain names.

   RFC 3315 Section 17.2.2 [RFC3315] describes how a DHCPv6 client and
   server negotiate configuration values using the Option Request Option
   (OPTION_ORO).  As a convenience to the reader, we mention here that a
   server will not reply with a DHCPv4-over-IPv6 option if the client
   has not explicitly enumerated it in its Option Request Option.  In
   other words, server SHOULD send this option only if client explicitly
   requested it in ORO.

5.  DHCPv6 Client Behavior

   A client that supports the DHCPv4 over IPv6 functionality and
   conforms to this specification MUST include OPTION_DHCP4_OVER_V6 on
   its OPTION_ORO.

   Because it requires DNS name to address resolution, the client SHOULD
   also wish to include the OPTION_DNS_SERVERS [RFC3646] option on its

   If the client receives the DHCPv4-over-IPv6 option, it MUST verify
   the option contents as described in Section 3.

   If the CRA entity receives more than one DHCPv4-over-IPv6 option, it
   MUST use only one instance of that option.

   If the DHCPv4-over-IPv6 option contains more than one FQDN, as
   distinguished by the presence of multiple root labels, the CRA entity
   system MUST use only the first FQDN listed in configuration.  It
   SHOULD warn its operator about such condition.

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   The CRA entity performs standard DNS resolution using the provided
   FQDN to resolve a AAAA Resource Record, as defined in [RFC3596] and
   STD 13 [RFC1034] [RFC1035].

   If any DNS response contains more than one IPv6 address (probably for
   redundancy and high availability consideration), the CRA entity picks
   only one IPv6 address and uses it as a DHCPv4-over-IPv6 transport
   endpoint for the interface being configured in the current message
   exchange.  The CRA system MUST NOT establish more than one transport
   at the same time per interface.

   Note that a CRA system may have multiple network interfaces, and
   these interfaces may be configured differently; some may be connected
   to networks that call for DHCPv4-over-IPv6, and some may be connected
   to networks that are using normal dual stack or other means.  The CRA
   entity should approach this specification on an interface-by-
   interface basis.  For example, if the CRA entity is attached to
   multiple networks that provide the DHCPv4-over-IPv6 option, then the
   CRA entity MUST configure a DHCPv4 over IPv6 transport for each
   interface separately as each transport provides IPv4 connectivity for
   each distinct interface.  Means to bind a DHCPv4-over-IPv6 transport
   configuration to a given interface in a multiple interfaces device
   are out of scope of this document.

6.  Security Considerations

   This document does not present any new security issues, but as with
   all DHCPv6-derived configuration state, it is completely possible
   that the configuration is being delivered by a third party (Man In
   The Middle).  As such, there is no basis to trust the access the
   address of which is provisioned following this specification, and it
   should not therefore bypass any security mechanisms such as IP

   It should be noted that DHCPv4 over IPv6 traffic may bypass existing
   firewalls that are typically configured to drop incoming outside
   DHCPv4 over IPv4 and DHCPv6 over IPv6 traffic.

   RFC 3315 [RFC3315] discusses DHCPv6-related security issues.

   [RFC6333] discusses DS-Lite related security issues.

7.  IANA Considerations

   IANA is kindly requested to allocate DHCPv6 option code TBD to the
   OPTION_DHCP4_OVER_V6.  The value should be added to the DHCPv6 option

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   code space defined in Section 24.3 of [RFC3315].

8.  Acknowledgements

   Authors would like to thank nobody so far, as we have not received
   any comments yet.

   This work has been partially supported by the Polish Ministry of
   Science and Higher Education under the European Regional Development
   Fund, Grant No.  POIG.01.01.02-00-045/09-00 (Future Internet
   Engineering Project).

9.  Normative References

              Cui, Y., Wu, P., Wu, J., and T. Lemon, "DHCPv4 over IPv6
              Transport", draft-ietf-dhc-dhcpv4-over-ipv6-02 (work in
              progress), March 2012.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
              "DNS Extensions to Support IP Version 6", RFC 3596,
              October 2003.

   [RFC3646]  Droms, R., "DNS Configuration options for Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              December 2003.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

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Authors' Addresses

   Tomasz Mrugalski
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City, CA  94063

   Phone: +1 650 423 1345

   Peng Wu
   Tsinghua University
   Beijing  100084


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