wdiff rfc8026.original rfc8026.txt

Softwire WG
Internet Engineering Task Force (IETF) M. Boucadair
Internet-Draft
Request for Comments: 8026 Orange
Intended status:
Category: Standards Track I. Farrer
Expires: April 3, 2017
ISSN: 2070-1721 Deutsche Telekom
September 30,
November 2016

Unified IPv4-in-IPv6 Softwire CPE: A DHCPv6-based Customer Premises Equipment
(CPE): a DHCPv6-Based Prioritization Mechanism
draft-ietf-softwire-unified-cpe-08

Abstract

In IPv6-only provider networks, transporting IPv4 packets
encapsulated in IPv6 is a common solution to the problem of IPv4
service continuity. 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
specifies a DHCPv6 option option, whereby a single CPE instance of Customer
Premises Equipment (CPE) can interwork with all of the standardized
and proposed approaches to providing encapsulated
IPv4 in IPv6 IPv4-in-IPv6
services by providing a prioritization mechanism.

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].

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 an Internet Standards Track document.

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

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on April 3, 2017.
http://www.rfc-editor.org/info/rfc8026.

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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. Requirements Language . . . . . . . . . . . . . . . . 4
1.2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. DHCPv6 S46 Priority Option . . . . . . . . . . . . . . . 4 5
1.4. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . 5
1.5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . 6
2. Operator Deployment Considerations for Deploying Multiple
Sotfwire
Softwire Mechanisms . . . . . . . . . . . . . . . . . . . . . 6
2.1. Client Address Planning . . . . . . . . . . . . . . . . . 6 7
2.2. Backwards Compatability with Existing Softwire Clients . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8
4.1. S46 Mechanisms and their Their Identifying Option Codes . . . . 8
5. Acknowledgements References . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . 9
5.1. Normative References . . . . . . . . . . . . . . . . . . 9
5.2. Informative References . . . . 8
6.1. Normative References . . . . . . . . . . . . . 9
Acknowledgements . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9 . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10

1. Introduction

IPv4 service continuity is one of the major technical challenges
which that
must be considered during IPv6 migration. Over the past few years, a
number of different approaches have been developed to assist with
this problem (e.g., as described in [RFC6333], [RFC7596], or and
[RFC7597]). These approaches, referred to as 'S46 mechanisms' "S46 mechanisms" in
this document, exist in order to meet the particular deployment,
scaling, addressing addressing, and other requirements of different service provider's
providers' networks.

A common feature shared between among all of the differing modes is the
integration of softwire tunnel end-point endpoint functionality into the
Customer Premise Premises Equipment (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 S46
mechanism enabled in order to support a diverse CPE population with
differing client functionality, such as during a migration between
mechanisms,
mechanisms or where services require specific supporting softwire
architectures.

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

A number of DHCPv6 options for the provisioning of softwires have
been standardized:

RFC6334

RFC 6334 Defines DHCPv6 option 64 for configuring Basic Bridging
BroadBand (B4, [RFC6333]) (B4) [RFC6333] elements with the IPv6 address of
the Address Family Transition Router (AFTR, [RFC6333]).
RFC7341 (AFTR) [RFC6333].

RFC 7341 Defines DHCPv6 option 88 for configuring the address of a
DHCPv4 over DHCPv6
DHCPv4-over-DHCPv6 server, which can then be used by a
softwire client for obtaining further configuration.
RFC7598

RFC 7598 Defines DHCPv6 options 94, 95 95, and 96 for provisioning
Mapping of Address and Port with Encapsulation (MAP-E, [RFC7597]), (MAP-E)
[RFC7597], Mapping of Address and Port using Translation (MAP-T,
[RFC7599]),
(MAP-T) [RFC7599], and Lightweight 4over6 [RFC7596]
respectively.

This document describes a DHCPv6 based DHCPv6-based prioritization method method, whereby
a CPE which that supports several S46 mechanisms and receives configuration
for more than one can prioritise prioritize which mechanism to use. The method
requires no server side server-side logic to be implemented and only uses a
simple S46 mechanism prioritization to be implemented in the CPE.

The prioritization method as described here does not provide
redundancy between S46 mechanisms for the client. I.e. If That is, if the
highest priority S46 mechanism which that has been provisioned to the
client is not available for any reason, the means for identifying
this and falling back to the S46 mechanism with the next highest
priority is not in the scope of this document.

1.1. Terminology

This document makes use of the following terms:

o Address Family Transition Router (AFTR): is the The IPv4-in-IPv6 tunnel
termination point and the NAT44 Network Address Translator IPv4/IPv4
(NAT44) function deployed in the operator's network [RFC6333].

o Border Relay (BR): a A MAP-enabled router managed by the service
provider at the edge of a MAP domain. A BR has at least an
IPv6-enabled interface and an IPv4 interface connected to the
native IPv4 network [RFC7597].

o Customer Premise Premises Equipment (CPE): denotes Denotes the equipment at the
customer edge that terminates the customer end of an IPv6
transitional tunnel. In some documents (e.g., [RFC7597]), this
functional entity is called CE (Customer Edge). the Customer Edge (CE).

1.1.1. 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 [RFC2119].

1.2. Rationale

The following rationale has been adopted for this document:

(1) Simplify Simplified solution migration paths: Define unified CPE
behavior, allowing for smooth migration between the different s46
S46 mechanisms.

(2) Deterministic CPE co-existence coexistence behavior: Specify the behavior
when several S46 mechanisms co-exist coexist in the CPE.

(3) Deterministic service provider co-existence coexistence behavior: Specify the
behavior when several modes co-exist coexist in the service providers
network.

(4) Re-usability: Reusability: Maximize the re-use reuse of existing functional blocks
including tunnel end-points, port restricted NAPT44, endpoints, the port-restricted Network Address
Port Translator IPv4/IPv4 (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.

1.3. DHCPv6 S46 Priority Option

The S46 Priority Option is used to convey a priority order of IPv4
service continuity mechanisms. Figure 1 shows the format of the S46
Priority 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_PRIORITY | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| s46-option-code | s46-option-code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | s46-option-code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: S46 Priority Option

o option-code: OPTION_S46_PRIORITY (TBD) (111)

o option-length: >=2 and a multiple of 2, in octets.

o s46-option-code: 16-bits long IANA registered 16-bit IANA-registered option code of the DHCPv6
option which that is used to identify the softwire mechanism. S46 mechanism
mechanisms are prioritized in the appearance order in the S46
Priority Option.

Codes in OPTION_S46_PRIORITY are processed in order; in the event
that if a client
receives more than one s46-option-code with a particular value, this it
should consider this case to be considered as invalid. DHCP servers MAY validate
the list of s46-option-code values to detect invalid values and
duplicates. The option MUST contain at least one s46-
option-code. s46-option-code.

1.4. DHCPv6 Client Behavior

Clients MAY request option OPTION_S46_PRIORITY, the OPTION_S46_PRIORITY option, as defined in
[RFC3315], Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7.
As a convenience to the reader, we mention here that the client
includes requested option codes in the Option Request Option.

Upon receipt of a DHCPv6 Advertise message from the server containing
OPTION_S46_PRIORITY
OPTION_S46_PRIORITY, the client performs the following steps:

1. Check the contents of the DHCPv6 message for options containing
valid S46 mechanism configuration. A candidate list of possible
S46 mechanisms is created from these option codes.

2. Check the contents of OPTION_S46_PRIORITY for the DHCPv6 option
codes contained in the included s46-option-code fields. From
this, an S46 mechanism priority list is created, ordered from
highest to lowest following the appearance order.

3. Sequentially check the priority list against the candidate list
until a match is found.

4. When a match is found, the client MUST configure the resulting
S46 mechanism.

In the event that no match is found between the priority list and the
candidate list, the client MAY proceed with configuring one or more
of the provisioned S46 softwire mechanism(s). In this case, which
mechanism(s) are chosen by the client is implementation-specific implementation specific and
not defined here.

If an invalid OPTION_S46_PRIORITY option is received, the client MAY
proceed with configuring the provisioned S46 mechanisms as if
OPTION_S46_PRIORITY had not been received.

If an unknown option code is received in the OPTION_S46_PRIORITY
option, the client MUST skip it and continue processing other listed
option codes if they exist. The initial option codes that are
allowed to be included in a an OPTION_S46_PRIORITY option are listed in
Section 4.1.

1.5. DHCPv6 Server Behavior

Sections 17.2.2 and 18.2 of [RFC3315] govern server operation in
regards
regard to option assignment. As a convenience to the reader, we
mention here that the server will send a particular option code only
if configured with specific values for that option code and if the
client requested it.

Option OPTION_S46_PRIORITY is a singleton. Servers MUST NOT send
more than one instance of the OPTION_S46_PRIORITY option.

2. Operator Deployment Considerations for Deploying Multiple Sotfwire Softwire
Mechanisms

The following sub-sections subsections describe some considerations for operators
who are planning on implementing multiple softwire mechanisms in
their network (e.g., during a migration between mechanisms).

2.1. Client Address Planning

As an operator's available IPv4 resources are likely to be limited,
it may be desirable to use a common range of IPv4 addresses across
all of the active Softwire softwire mechanisms. However, this is likely to
result in difficulties in routing ingress IPv4 traffic to the correct
Border Relay (BR)/AFTR instance (BR) / AFTR instance, which is actively serving a given
CE. For example, a client which that is configured to use MAP-E may send
its traffic to the MAP-E BR, but BR; however, on the return path, the ingress
IP traffic gets routed to a MAP-T BR. The resulting translated
packet that gets forwarded to the MAP-E client will be dropped.

Therefore, operators are advised to use separate IPv4 pools for each
of the different mechanisms to simplify planning and IPv4 routing.

For IPv6 planning planning, there is less of a constraint as the BR/AFTR
elements for the different mechanisms can contain configuration for
overlapping the client's IPv6 addresses, providing only provided that one mechanism
is actively serving a given client at a time. However, the IPv6
address that is used as the tunnel concentrator's endpoint (BR/AFTR
address) needs to be different for each mechanisms mechanism to ensure correct
operation.

2.2. Backwards Compatability with Existing Softwire Clients

Deployed clients which that can support multiple softwire mechanisms, but
do not implement the prioritization mechanism described here may
require additional planning. In this scenario, the CPE would request
configuration for all of the supported softwire mechanisms in its
DHCPv6 Option Request Option (ORO), but would not request
OPTION_S46_PRIORITY. By default, the DHCPv6 server will respond with
configuration for all of the requested mechanisms mechanisms, which could result
in unpredictable and unwanted client configuration.

In this scenario, it may be necessary for the operator to implement
logic within the DHCPv6 server to identify such clients and only
provision them with configuration for a single softwire mechanism.
It should be noted that this can lead to complexity and reduced
scalability in the DHCPv6 server implementation due to the addition additional
DHCPv6 message processing overhead.

3. Security Considerations

Security considerations discussed in [RFC6334] and [RFC7598] apply
for this document.

Misbehaving intermediate nodes may alter the content of the S46
Priority Option. This may lead to setting a different IPv4 service
continuity mechanism than the one initially preferred by the network
side. Also, a misbehaving node may alter the content of the S46
Priority Option and other DHCPv6 options (e.g., DHCPv6 Option #64 64 or
#90)
90) so that the traffic is intercepted by an illegitimate node.
Those attacks are not unique to the S46 Priority Option but are
applicable to any DHCPv6 option that can be altered by a misbehaving
intermediate node.

4. IANA Considerations

IANA is kindly requested to allocate has allocated the following DHCPv6 option code:

TBD for

111 OPTION_S46_PRIORITY

All values should be added to the DHCPv6 option code space defined in
Section 24.3 of [RFC3315].

4.1. S46 Mechanisms and their Their Identifying Option Codes

This document requests that

IANA create has created a new registry entitled titled "Option Codes permitted in the
S46 Priority Option". This registry
will enumerate enumerates the set of DHCPv6 Option Codes
option codes that can be included in the OPTION_S46_PRIORITY option.
Options may be added to this list using the IETF Review process
described in Section 4.1 of [RFC5226].

The following table shows the option codes which that are currently defined
and the S46 mechanisms which that they represent. The contents of this
table shows the format and the initial values for the new registry.
Option codes that have not been requested to be added according to
the stated procedure should not be mentioned at all in the table, and
they should not be listed as "reserved" or "unassigned". The valid
range of values for the registry is the range of DHCPv6
Option Codes option codes
(1-65535).

+-------------+--------------------+-----------+
| Option Code | S46 Mechanism | Reference |
+-------------+--------------------+-----------+
| 64 | DS-Lite | [RFC6334] |
| 88 | DHCPv4 over DHCPv6 | [RFC7341] |
| 94 | MAP-E | [RFC7598] |
| 95 | MAP-T | [RFC7598] |
| 96 | Lightweight 4over6 | [RFC7598] |
+-------------+--------------------+-----------+

Table 1: DHCPv6 Option to S46 Mechanism Mappings

5. Acknowledgements

Many thanks to O. Troan, S. Barth. A. Yourtchenko, B. Volz, T.
Mrugalski, J. Scudder, P. Kyzivat, F. Baker, and B. Campbell for
their input and suggestions.

6. References

6.1.

5.1. 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>.

[RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
RFC 6334, DOI 10.17487/RFC6334, August 2011,
<http://www.rfc-editor.org/info/rfc6334>.

[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
RFC 7341, DOI 10.17487/RFC7341, August 2014,
<http://www.rfc-editor.org/info/rfc7341>.

[RFC7598] Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
Configuration of Softwire Address and Port-Mapped
Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
<http://www.rfc-editor.org/info/rfc7598>.

6.2.

5.2. Informative References

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<http://www.rfc-editor.org/info/rfc6333>.

[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>.

Acknowledgements

Many thanks to O. Troan, S. Barth, A. Yourtchenko, B. Volz, T.
Mrugalski, J. Scudder, P. Kyzivat, F. Baker, and B. Campbell for
their input and suggestions.

Authors' Addresses

Mohamed Boucadair
Orange
Rennes
France

Email: mohamed.boucadair@orange.com

Ian Farrer
Deutsche Telekom
Germany

Email: ian.farrer@telekom.de