Network Working Group J. Laganier

Network Working Group J. Laganier
Request for Comments: 5203 DoCoMo Euro-Labs
Category: Experimental T. Koponen
HIIT
L. Eggert
Nokia
April 2008

Host Identity Protocol (HIP) Registration Extension

Status of This Memo

This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.

Abstract

This document specifies a registration mechanism for the Host
Identity Protocol (HIP) that allows hosts to register with services,
such as HIP rendezvous servers or middleboxes.

1. Introduction

This document specifies an extension to the Host Identity Protocol
(HIP) [RFC5201]. The extension provides a generic means for a host
to register with a service. The service may, for example, be a HIP
rendezvous server [RFC5204] or a middlebox [RFC3234].

This document makes no further assumptions about the exact type of
service. Likewise, this document does not specify any mechanisms to
discover the presence of specific services or means to interact with
them after registration. Future documents may describe those
operations.

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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2. Terminology

In addition to the terminology defined in the HIP Architecture
[RFC4423], the HIP specification [RFC5201], and the HIP Rendezvous
Extension [RFC5204], this document defines and uses the following
terms:

Requester:
a HIP node registering with a HIP registrar to request
registration for a service.

Registrar:
a HIP node offering registration for one or more services.

Service:
a facility that provides requesters with new capabilities or
functionalities operating at the HIP layer. Examples include
firewalls that support HIP traversal or HIP rendezvous servers.

Registration:
shared state stored by a requester and a registrar, allowing the
requester to benefit from one or more HIP services offered by the
registrar. Each registration has an associated finite lifetime.
Requesters can extend established registrations through re-
registration (i.e., perform a refresh).

Registration Type:
an identifier for a given service in the registration protocol.
For example, the rendezvous service is identified by a specific
registration type.

3. HIP Registration Extension Overview

This document does not specify the means by which a requester
discovers the availability of a service, or how a requester locates a
registrar. After a requester has discovered a registrar, it either
initiates HIP base exchange or uses an existing HIP association with
the registrar. In both cases, registrars use additional parameters,
which the remainder of this document defines, to announce their
quality and grant or refuse registration. Requesters use
corresponding parameters to register with the service. Both the
registrar and the requester MAY also include in the messages
exchanged additional HIP parameters specific to the registration type
implicated. Other documents will define parameters and how they
shall be used. The following sections describe the differences
between this registration handshake and the standard HIP base
exchange [RFC5201].

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3.1. Registrar Announcing Its Ability

A host that is capable and willing to act as a registrar SHOULD
include a REG_INFO parameter in the R1 packets it sends during all
base exchanges. If it is currently unable to provide services due to
transient conditions, it SHOULD include an empty REG_INFO, i.e., one
with no services listed. If services can be provided later, it
SHOULD send UPDATE packets indicating the current set of services
available in a new REG_INFO parameter to all hosts it is associated
with.

3.2. Requester Requesting Registration

To request registration with a service, a requester constructs and
includes a corresponding REG_REQUEST parameter in an I2 or UPDATE
packet it sends to the registrar.

If the requester has no HIP association established with the
registrar, it SHOULD send the REG_REQUEST at the earliest
possibility, i.e., in the I2 packet. This minimizes the number of
packets that need to be exchanged with the registrar. A registrar
MAY end a HIP association that does not carry a REG_REQUEST by
including a NOTIFY with the type REG_REQUIRED in the R2. In this
case, no HIP association is created between the hosts. The
REG_REQUIRED notification error type is 51.

3.3. Registrar Granting or Refusing Service(s) Registration

Once registration has been requested, the registrar is able to
authenticate the requester based on the host identity included in I2.
It then verifies that the host identity is authorized to register
with the requested service(s), based on local policies. The details
of this authorization procedure depend on the type of requested
service(s) and on the local policies of the registrar, and are
therefore not further specified in this document.

After authorization, the registrar includes a REG_RESPONSE parameter
in its response, which contains the service type(s) for which it has
authorized registration, and zero or more REG_FAILED parameters
containing the service type(s) for which it has not authorized
registration or registration has failed for other reasons. This
response can be either an R2 or an UPDATE message, respectively,
depending on whether the registration was requested during the base
exchange, or using an existing association. In particular,
REG_FAILED with a failure type of zero indicates the service(s)
type(s) that require further credentials for registration.

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If the registrar requires further authorization and the requester has
additional credentials available, the requester SHOULD try to
register again with the service after the HIP association has been
established. The precise means of establishing and verifying
credentials are beyond the scope of this document and are expected to
be defined in other documents.

Successful processing of a REG_RESPONSE parameter creates
registration state at the requester. In a similar manner, successful
processing of a REG_REQUEST parameter creates registration state at
the registrar and possibly at the service. Both the requester and
registrar can cancel a registration before it expires, if the
services afforded by a registration are no longer needed by the
requester, or cannot be provided any longer by the registrar (for
instance, because its configuration has changed).

+-----+ I1 +-----+-----+
| |--------------------->| | S1 |
| |<---------------------| | |
| | R1(REG_INFO:S1,S2) | +-----+
| RQ | | R | S2 |
| | I2(REG_REQ:S1) | | |
| |--------------------->| +-----+
| |<---------------------| | S3 |
| | R2(REG_RESP:S1) | | |
+-----+ +-----+-----+

A requester (RQ) registers with a registrar (R) of services (S1) and
(S2), with which it has no current HIP association.

+-----+ +-----+-----+
| | UPDATE(REG_INFO:S) | | |
| |<---------------------| | |
| RQ |--------------------->| R | S |
| | UPDATE(REG_REQ:S) | | |
| | UPDATE(REG_RESP:S) | | |
| |<---------------------| | |
+-----+ +-----+-----+

A requester (RQ) registers with a registrar (R) of services (S), with
which it currently has a HIP association established.

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4. Parameter Formats and Processing

This section describes the format and processing of the new
parameters introduced by the HIP registration extension.

4.1. Encoding Registration Lifetimes with Exponents

The HIP registration uses an exponential encoding of registration
lifetimes. This allows compact encoding of 255 different lifetime
values ranging from 4 ms to 178 days into an 8-bit integer field.
The lifetime exponent field used throughout this document MUST be
interpreted as representing the lifetime value 2^((lifetime - 64)/8)
seconds.

4.2. REG_INFO

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min Lifetime | Max Lifetime | Reg Type #1 | Reg Type #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ... | Reg Type #n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Padding +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type 930
Length Length in octets, excluding Type, Length, and Padding.
Min Lifetime Minimum registration lifetime.
Max Lifetime Maximum registration lifetime.
Reg Type The registration types offered by the registrar.

Other documents will define specific values for registration types.
See Section 7 for more information.

Registrars include the parameter in R1 packets in order to announce
their registration capabilities. The registrar SHOULD include the
parameter in UPDATE packets when its service offering has changed.
HIP_SIGNATURE_2 protects the parameter within the R1 packets.

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4.3. REG_REQUEST

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime | Reg Type #1 | Reg Type #2 | Reg Type #3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ... | Reg Type #n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Padding +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type 932
Length Length in octets, excluding Type, Length, and Padding.
Lifetime Requested registration lifetime.
Reg Type The preferred registration types in order of preference.

Other documents will define specific values for registration types.
See Section 7 for more information.

A requester includes the REG_REQUEST parameter in I2 or UPDATE
packets to register with a registrar's service(s). If the
REG_REQUEST parameter is in an UPDATE packet, the registrar MUST NOT
modify the registrations of registration types that are not listed in
the parameter. Moreover, the requester MUST NOT include the
parameter unless the registrar's R1 packet or latest received UPDATE
packet has contained a REG_INFO parameter with the requested
registration types.

The requester MUST NOT include more than one REG_REQUEST parameter in
its I2 or UPDATE packets, while the registrar MUST be able to process
one or more REG_REQUEST parameters in received I2 or UPDATE packets.

When the registrar receives a registration with a lifetime that is
either smaller or greater than the minimum or maximum lifetime,
respectively, then it SHOULD grant the registration for the minimum
or maximum lifetime, respectively.

HIP_SIGNATURE protects the parameter within the I2 and UPDATE
packets.

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4.4. REG_RESPONSE

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime | Reg Type #1 | Reg Type #2 | Reg Type #3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ... | Reg Type #n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Padding +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type 934
Length Length in octets, excluding Type, Length, and Padding.
Lifetime Granted registration lifetime.
Reg Type The granted registration types in order of preference.

Other documents will define specific values for registration types.
See Section 7 for more information.

The registrar SHOULD includes an REG_RESPONSE parameter in its R2 or
UPDATE packet only if a registration has successfully completed.

The registrar MUST NOT include more than one REG_RESPONSE parameter
in its R2 or UPDATE packets, while the requester MUST be able to
process one or more REG_RESPONSE parameters in received R2 or UPDATE
packets.

The requester MUST be prepared to receive any registration lifetime,
including ones beyond the minimum and maximum lifetime indicated in
the REG_INFO parameter. It MUST NOT expect that the returned
lifetime will be the requested one, even when the requested lifetime
falls within the announced minimum and maximum.

HIP_SIGNATURE protects the parameter within the R2 and UPDATE
packets.

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4.5. REG_FAILED

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failure Type | Reg Type #1 | Reg Type #2 | Reg Type #3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ... | Reg Type #n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Padding +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type 936
Length Length in octets, excluding Type, Length, and Padding.
Failure Type Reason for failure.
Reg Type The registration types that failed with the specified
reason.

Failure Type Reason
------------ --------------------------------------------
0 Registration requires additional credentials
1 Registration type unavailable
2-200 Unassigned
201-255 Reserved by IANA for private use

Other documents will define specific values for registration types.
See Section 7 for more information.

A failure type of zero means a registrar requires additional
credentials to authorize a requester to register with the
registration types listed in the parameter. A failure type of one
means that the requested service type is unavailable at the
registrar. Failure types other than zero (0) and one (1) have not
been defined.

The registrar SHOULD include the REG_FAILED parameter in its R2 or
UPDATE packet, if registration with the registration types listed has
not completed successfully and a requester is asked to try again with
additional credentials.

HIP_SIGNATURE protects the parameter within the R2 and UPDATE
packets.

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5. Establishing and Maintaining Registrations

Establishing and/or maintaining a registration may require additional
information not available in the transmitted REG_REQUEST or
REG_RESPONSE parameters. Therefore, registration type definitions
MAY define dependencies for HIP parameters that are not defined in
this document. Their semantics are subject to the specific
registration type specifications.

The minimum lifetime both registrars and requesters MUST support is
10 seconds, while they SHOULD support a maximum lifetime of 120
seconds, at least. These values define a baseline for the
specification of services based on the registration system. They
were chosen to be neither too short nor too long, and to accommodate
for existing timeouts of state established in middleboxes (e.g., NATs
and firewalls.)

A zero lifetime is reserved for canceling purposes. Requesting a
zero lifetime for a registration type is equal to canceling the
registration of that type. A requester MAY cancel a registration
before it expires by sending a REG_REQ to the registrar with a zero
lifetime. A registrar SHOULD respond and grant a registration with a
zero lifetime. A registrar (and an attached service) MAY cancel a
registration before it expires, at its own discretion. However, if
it does so, it SHOULD send a REG_RESPONSE with a zero lifetime to all
registered requesters.

6. Security Considerations

This section discusses the threats on the HIP registration protocol,
and their implications on the overall security of HIP. In
particular, it argues that the extensions described in this document
do not introduce additional threats to HIP.

The extensions described in this document rely on the HIP base
exchange and do not modify its security characteristics, e.g.,
digital signatures or HMAC. Hence, the only threat introduced by
these extensions is related to the creation of soft registration
state at the registrar.

Registrars act on a voluntary basis and are willing to accept being a
responder and then to create HIP associations with a number of
previously unknown hosts. Because they have to store HIP association
state anyway, adding a certain amount of time-limited HIP
registration state should not introduce any serious additional
threats, especially because HIP registrars may cancel registrations
at any time at their own discretion, e.g., because of resource
constraints during an attack.

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7. IANA Considerations

This section is to be interpreted according to the Guidelines for
Writing an IANA Considerations Section in RFCs [RFC2434].

This document updates the IANA Registry for HIP Parameter Types by
assigning new HIP Parameter Types values for the new HIP Parameters
defined in this document:

o REG_INFO (defined in Section 4.2)

o REG_REQUEST (defined in Section 4.3)

o REG_RESPONSE (defined in Section 4.4)

o REG_FAILED (defined in Section 4.5)

IANA has allocated the Notify Message Type code 51 for the
REG_REQUIRED notification error type in the Notify Message Type
registry.

IANA has opened a new registry for registration types. This document
does not define registration types but makes the following
reservations:

Reg Type Service
-------- -------
0-200 Unassigned
201-255 Reserved by IANA for private use

Adding a new type requires new IETF specifications.

IANA has opened a new registry for registration failure types. This
document makes the following failure type definitions and
reservations:

Failure Type Reason
------------ --------------------------------------------
0 Registration requires additional credentials
1 Registration type unavailable
2-200 Unassigned
201-255 Reserved by IANA for private use

Adding a new type requires new IETF specifications.

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8. Acknowledgments

The following people (in alphabetical order) have provided thoughtful
and helpful discussions and/or suggestions that have helped to
improve this document: Jeffrey Ahrenholz, Miriam Esteban, Mika Kousa,
Pekka Nikander, and Hannes Tschofenig.

9. References

9.1. Normative References

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

[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.

[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., Ed., and T.
Henderson, "Host Identity Protocol", RFC 5201, April 2008.

9.2. Informative References

[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, February 2002.

[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.

[RFC5204] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", RFC 5204, April 2008.

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Authors' Addresses

Julien Laganier
DoCoMo Communications Laboratories Europe GmbH
Landsberger Strasse 312
Munich 80687
Germany

Phone: +49 89 56824 231
EMail: [email protected]
URI: http://www.docomolab-euro.com/

Teemu Koponen
Helsinki Institute for Information Technology
Advanced Research Unit (ARU)
P.O. Box 9800
Helsinki FIN-02015-HUT
Finland

Phone: +358 9 45 1
EMail: [email protected]
URI: http://www.hiit.fi/

Lars Eggert
Nokia Research Center
P.O. Box 407
Nokia Group 00045
Finland

Phone: +358 50 48 24461
EMail: [email protected]
URI: http://research.nokia.com/people/lars_eggert/

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