Softwire WG T. Mrugalski, Ed.
Internet-Draft ISC
Intended status: Standards Track M. Boucadair
Expires: May 03, 2012 France Telecom
O. Troan
X. Deng
Orange-France Telecom
C.X. Bao
Tsinghua University
October 31, 2011

DHCPv6 Options for Mapping of Address and Port


Generic mechanism for mapping between an IPv4 prefix, address or parts of thereof, and transport layer between ports and an IPv6 prefix or address is specified in [I-D.mdt-softwire-mapping-address-and-port]. This is a companion document that specifies provisioning mechanism of MAP rules. It defines DHCPv6 options which are meant to be used between Customer Edge (CE) devices and DHCPv6 server to obtain necessary parameters to configure MAP rules. Since specification of MAP architecture is still expected to evolve, DHCPv6 options may have to evolve too to fit the revised MAP specification.

Status of this Memo

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This Internet-Draft will expire on May 03, 2012.

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Table of Contents

1. Introduction

Mapping of Address and Port (MAP) defined in [I-D.mdt-softwire-mapping-address-and-port] is a mechanism for providing IPv4 connectivity service to end users over a service provider's IPv6 network. It defines both MAP Border Relay (BR) router that is located at the edge of a MAP domain and MAP Customer Edge (CE) that typically deployed at customers' location. In a residential broadband deployment, CE is sometimes referred to as a Residential Gateway (RG) or Customer Premises Equipment (CPE). A MAP CE may also be referred to simply as a "CE" within the context of MAP.

A typical MAP CE adopting MAP rules will serve a residential site with one WAN side interface, one or more LAN side interfaces. To operate properly, it requires one or more MAP rules and additional informations. In larger networks it is infeasible to configure such parameters manually. Therefore provisioning mechanism is required. Such mechanism is defined in this document. It leverages existing DHCPv6 [RFC3315] protocol to deliver necessary parameters to CE.

This document defines several DHCPv6 options that allow delivery of required information to configure CE. Configuration of the BR is outside of scope of this document. Definitions of used parameters are provided in [I-D.mdt-softwire-mapping-address-and-port].

Since specification of MAP architecture is still expected to evolve, DHCPv6 options may have to evolve too to fit the revised MAP specification.

Described proposal is not a dynamic port allocation mechanism.

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].

3. Provisioning mechanism

A typical MAP CE usually acts as a DHCPv6 client and requests options that are being provided by a DHCPv6 server located somewhere in ISP network. It would adopt three kinds of parameters independently:

4. DHCPv6 Options Format

DHCPv6 protocol is used for CE provisioning. Several new options are defined for conveying MAP-specific parameters. Their format and usage is defined in the following sections.

Discussion: As the exact parameters required to configure MAP rules and MAP in general are expected to change, this section is expected to be updated or even rewritten completely.

Discussion: Proposed layout assumes that several simple options are used. Such approach simplifies implementation as it is much easier for implementors to reuse existing code handling such options. This design choice comes at a cost, however. Clients must perform checks if provided set of options is complete. Alternatively, it would be possible to define one complex option that contains all mandatory parameters.

Discussion: It should be noted that initial concept of 4rd provisioning was presented in DHC working group meeting. It used one complex option to convey all required parameters. Strong suggestion from DHC WG was to use several simpler options. Options (possibly nested) are preferred over conditional option formatting. See DHCP option guidelines document [I-D.ietf-dhc-option-guidelines]).

4.1. MAP Options Cardinality

MAP rule is defined in [I-D.mdt-softwire-mapping-address-and-port], Section 4.

Discussion: If you want additional parameter added to the OPTION_MAP_RULE option, please update [I-D.mdt-softwire-mapping-address-and-port] first.

In each REPLY message, server that supports MAP configuration MUST include exactly one OPTION_MAP_FLAGS option.

MAP_FLAGS option MUST include one or more OPTION_MAP_RULE options.

For proper operation, additional parameters obtained via other options are necessary. In particular, L parameter is equal to a length of a prefix delegated to CE, conveyed in OPTION_IA_PD and IAPREFIX, as defined in [RFC3633]. As there is already defined mechanism to provision this value, it is not mentioned in MAP options. Nevertheless, it is required for proper MAP rule configuration.

4.2. MAP Flags Option

. This option specifies MAP flags. Currently the only defined flag is T - transport mode. Other flags that affect all mapping rules or the whole MAP domain may be specified here at a later date.

Each MAP_FLAGS option MUST contain one or more MAP Rule Options.

 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_MAP_FLAGS       |         option-length         |
|   reserved  |T|

4.3. MAP Rule Option

This option represents a single MAP Rule. Depending on deployment mode, each CE may require one or more MAP Rules to operate properly.

Server includes one or more MAP Rule Options in MAP Flags option.

Server MAY send more than one MAP Rule Option, if it is configured to do so. Clients MUST NOT send MAP Rule 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_MAP_RULE        |         option-length         |
|    rule-id    |  prefix4-len  |  prefix6-len  |    ea-len     |
|                                                               |
|                        rule-ipv6-prefix                       |
|                                                               |
|                                                               |
|                       rule-ipv4-prefix                        |
|                                                               |
.                rule sub-options (variable length)             .
.                                                               .

Each rule is identified with a rule-id. Rule-id MUST be unique within each CE. Rule ID also defines rule type. Rule-id 0 denotes default rule. Each CE configuration providioned by DHCPv6 server MUST provide exactly one default rule (with rule-id set to 0). Additional rules MAY be provided as required, but they MUST NOT use rule-id value of 0. Rules with rule-id smaller than 128 are Basic Mapping Rules. Rules with rule-id equal or greater than 128 are Forwarding Mapping Rules.

Note that the default mapping rule is a simplified version of Basic Mapping Rule. While it reuses the same DHCPv6 option format, Default Mapping Rule uses only Rule IPv6 prefix, Rule IPv6 Prefix Length and IPv4 address that denotes BR IPv4 address. All other parameters are ignored for Default Mapping Rule.

Discussion: Remi Despres pointed out that not all of prefix4len + prefix6-len + ea-len + excluded ports + off are needed. Only 4 of these are independent, so one of them will be removed.

4.4. Port Parameters Option

Port Parameters Option specifies Rule Port Paramters. It MAY appear as sub-option in OPTION_MAP_RULE option. It MUST NOT appear directly in a message.

See [I-D.mdt-softwire-mapping-address-and-port], Section 4.1 for detailed description of Port mapping algorithm.

 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_MAP_PORTPARAMS     |         option-length         |
|         excluded-ports        |A|  rsv  | off |

Map Port Parameters Option is optional. If it is not present, the following default values are to be assumed:

  1. Excluded ports: 0-1023 (excluded-ports field value is 1023)
  2. A: offset is for a (A field value is 0)
  3. Offset bits: 6 (off field value is 6)

If administrator wants to provision only one or two of those parameters, remaining fields SHOULD be set to their default value.

4.5. MAP Options Example

DHCPv6 server provisioning a single MAP Rule to a CE (DHCPv6 client) will convey the following MAP options in its messages:

    <MAP_RULE1 rule-id="0"/>
    <MAP_RULE2 rule-id="1"/>
    <MAP_RULE3 rule-id="2"/>

TODO: Make this a more detailed. This is more of a placeholder, than a real example.

5. DHCPv6 Server Behavior

RFC 3315 Section 17.2.2 [RFC3315] describes how a DHCPv6 client and server negotiate configuration values using the ORO. As a convenience to the reader, we mention here that a server will not reply with a MAP Rule Option if the client has not explicitly enumerated it on its Option Request Option.

Server conformant to this specification MUST allow configuration of one or more MAP Rule Options.

Server MUST transmist all configured instances of the Mapping Rule Options with all sub-options, if client requested it using OPTION_MAP_RULE in its Option Request Option (ORO). Server MUST transmit MAP Flags Option if client requested OPTION_MAP_FLAGS in its ORO.

Rules assignment is a stateless process from the server's perspective. Server does not need to maintain a state of rules provisioned to clients, track lifetimes, expire outdated rules etc. Server SHOULDs assign the same set of rules to all CEs in one MAP Domain, unless there are several classes of CEs defined, e.g. regular and premium users. In such case, each class of CEs is expected to get the same set of rules. Server is not expected to track MAP rules on a per CE basis. Exact assignment of specific rules to a specific CEs is outside of scope of this document.

6. DHCPv6 Client Behavior

Although other use cases are allowed, in typical use case CE will act as DHCPv6 client and will request MAP configuration to be assigned by the DHCPv6 server located in the ISP network. A client that supports MAP CE functionality and conforms to this specfication MUST include OPTION_MAP_RULE and OPTION_MAP_FLAGS in its ORO.

For proper operation, MAP CE client MUST also request IPv6 address (OPTION_IA_NA, defined in [RFC3315]) and prefix delegation (OPTION_IA_PD, defined in [RFC3633]). MAP CE client SHOULD NOT initiate DHCPv4 configuration as all parameters are delivered over DHCPv6.


If client receives more than one OPTION_MAP_RULE option, it MUST use all received instances. It MUST NOT use only the first one, while discarding remaining ones.

Note that system implementing MAP CE functionality may have multiple network interfaces, and these interfaces may be configured differently; some may be connected to networks that call for MAP, and some may be connected to networks that are using normal dual stack or other means. The MAP CE system should approach this specification on an interface-by-interface basis. For example, if the CE system is attached to multiple networks that provide the MAP Mapping Rule Option, then the CE system MUST configure a MAP connection (i.e. a translation or encapsulation) for each interface separately as each MAP provides IPv4 connectivity for each distinct interface. Means to bind a MAP configuration to a given interface in a multiple interfaces device are out of scope of this document.

7. IANA Considerations

IANA is kindly requested to allocate DHCPv6 option code referencing this document, delineating OPTION_MAP_RULE and OPTION_MAP_FLAGS.

8. Security Considerations

Implementation of 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 that the access over the MAP can be trusted, and it should not therefore bypass any security mechanisms such as IP firewalls.

Readers concerned with security of MAP provisioning over DHCPv6 are encouraged to familiarize with [I-D.ietf-dhc-secure-dhcpv6].

Section XX of [I-D.mdt-softwire-mapping-address-and-port] discusses security issues of the MAP mechanism.

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

Section 6 of [I-D.murakami-softwire-4rd] discusses 4rd related security issues that are partially applicable to MAP mechanism.

9. IANA Considerations

IANA is requested to allocate DHCPv6 option code TBD1 to the OPTION_MAP_FLAGS,TBD2 to OPTION_MAP_RULE and TBD3 to OPTION_MAP_PORTPARAMS. All three values should be added to the DHCPv6 option code space defined in Section 24.3 of [RFC3315].

10. Contributors

The members of the MAP design team are:

  1. Congxiao Bao
  2. Mohamed Boucadair
  3. Gang Chen
  4. Maoke Chen
  5. Wojciech Dec
  6. Xiaohong Deng
  7. Remi Despres
  8. Jouni Korhonen
  9. Xing Li
  10. Satoru Matsushima
  11. Tomasz Mrugalski
  12. Jacni Qin
  13. Qiong Sun
  14. Tina Tsou
  15. Ole Troan
  16. Dan Wing
  17. Leaf Yeh
  18. Jan Zorz

11. Acknowledgements

Authors would like to thank Xiaohong Deng, Congxiao Bao, Jacni Qin, Qiong Sun for their comments and suggestions.

12. References

12.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.mdt-softwire-mapping-address-and-port] Troan, O, "Mapping of Address and Port (MAP)", Internet-Draft draft-mdt-softwire-mapping-address-and-port-01, October 2011.
[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.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.

12.2. Informative References

[I-D.ietf-dhc-option-guidelines] Hankins, D, "Guidelines for Creating New DHCP Options", Internet-Draft draft-ietf-dhc-option-guidelines-07, October 2011.
[I-D.mrugalski-dhc-dhcpv6-4rd] Mrugalski, T, "DHCPv6 Options for IPv4 Residual Deployment (4rd)", Internet-Draft draft-mrugalski-dhc-dhcpv6-4rd-00, July 2011.
[I-D.boucadair-dhcpv6-shared-address-option] Boucadair, M, Levis, P, Grimault, J, Savolainen, T and G Bajko, "Dynamic Host Configuration Protocol (DHCPv6) Options for Shared IP Addresses Solutions", Internet-Draft draft-boucadair-dhcpv6-shared-address-option-01, December 2009.
[I-D.ietf-dhc-secure-dhcpv6] Jiang, S and S Shen, "Secure DHCPv6 Using CGAs", Internet-Draft draft-ietf-dhc-secure-dhcpv6-03, June 2011.
[I-D.murakami-softwire-4rd] Murakami, T, Troan, O and S Matsushima, "IPv4 Residual Deployment on IPv6 infrastructure - protocol specification", Internet-Draft draft-murakami-softwire-4rd-01, September 2011.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.

Authors' Addresses

Tomasz Mrugalski editor Internet Systems Consortium, Inc. 950 Charter Street Redwood City, CA 94063 USA Phone: +1 650 423 1345 EMail:
Mohamed Boucadair France Telecom Rennes, 35000 France EMail:
Ole Troan Cisco Systems, Inc. Telemarksvingen 20 Oslo, N-0655 Norway EMail:
Xiaohong Deng Orange-France Telecom Haidian district Beijing, 100190 China EMail:
Congxiao Bao CERNET Center/Tsinghua University Room 225, Main Building, Tsinghua University Beijing, 100084 CN Phone: +86 10-62785983 EMail: