WDIFF

draft-eronen-ipsec-ikev2-clarifications-02.txt --> draft-eronen-ipsec-ikev2-clarifications-03.txt

Network Working Group P. Eronen
Internet-Draft Nokia
Expires: September 25, December 3, 2005 P. Hoffman
VPN Consortium
March 27,
June 1, 2005

IKEv2 Clarifications and Implementation Guidelines
draft-eronen-ipsec-ikev2-clarifications-02.txt
draft-eronen-ipsec-ikev2-clarifications-03.txt

Status of this Memo

This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667.

By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she become becomes
aware will be disclosed, in accordance with
RFC 3668. Section 6 of BCP 79.

Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 25, December 3, 2005.

Abstract

This document clarifies many areas of the IKEv2 specification. It
does not to introduce any changes to the protocol, but rather
provides descriptions that are less prone to ambiguous
interpretations. The purpose of this document is to encourage the
development of interoperable implementations.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Authentication . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Data included in AUTH payload calculation . . . . . . . . 4
2.2 Hash function for RSA signatures . . . . . . . . . . . . . 5
2.3 Encoding method for RSA signatures . . . . . . . . . . . . 6
2.4 Identification type for EAP . . . . . . . . . . . . . . . 6
2.5 Identity for policy lookups when using EAP . . . . . . . . 7
2.6 EAP authentication and the AUTH payload . . . . . . . . . 7
2.7 Certificate encoding types . . . . . . . . . . . . . . . . 7
2.8 Shared key authentication and fixed PRF key size . . . . . 8
2.9 EAP authentication and fixed PRF key size . . . . . . . . 9
2.10 Matching ID payloads to certificate contents . . . . . . 9
3. Keying and rekeying . . . . . . . . . . . . . . . . . . . . 9
3.1 Semantics of the CREATE_CHILD_SA exchange . . . . . . . . 9
3.2 Rekeying the IKE_SA vs. reauthentication . . . . . . . . . 13
3.3 SPIs when rekeying the IKE_SA . . . . . . . . . . . . . . 13 14
3.4 SPI when rekeying a CHILD_SA . . . . . . . . . . . . . . . 14
3.5 Changing PRFs when rekeying the IKE_SA . . . . . . . . . . 14
3.6 Deleting vs. closing SAs . . . . . . . . . . . . . . . . . 14
3.7 Deleting a CHILD_SA pair . . . . . . 14 . . . . . . . . . . . 15
3.8 Deleting an IKE_SA . . . . . . . . . . . . . . . . . . . . 15
3.9 Who is the original initiator of IKE_SA . . . . . . . . . 15
4. Traffic selectors . . . . . . . . . . . . . . . . . . . . . 14 16
4.1 Semantics of complex traffic selector payloads . . . . . . 14 16
4.2 ICMP type/code in traffic selector payloads . . . . . . . 15 16
4.3 Mobility header in traffic selector payloads . . . . . . . 15 17
4.4 Narrowing the traffic selectors . . . . . . . . . . . . . 15 17
4.5 SINGLE_PAIR_REQUIRED . . . . . . . . . . . . . . . . . . . 16 17
4.6 Traffic selectors violating own policy . . . . . . . . . . 16 18
5. Configuration payloads . . . . . . . . . . . . . . . . . . . 17 19
5.1 Length of configuration attribute type field . . . . . . . 17 19
5.2 Requesting any INTERNAL_IP4/IP6_ADDRESS . . . . . . . . . 17 19
5.3 INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET . . . . . . . . . 18 19
5.4 INTERNAL_IP4_NETMASK . . . . . . . . . . . . . . . . . . . 20 22
5.5 Configuration payloads for IPv6 . . . . . . . . . . . . . 22 23
5.6 INTERNAL_IP6_ADDRESS prefix length . . . . . . . . . . . . 22 24
5.7 INTERNAL_IP6_NBNS . . . . . . . . . . . . . . . . . . . . 23 25
5.8 INTERNAL_ADDRESS_EXPIRY . . . . . . . . . . . . . . . . . 25
6. Miscellaneous issues . . . . . . . . . . . . . . . . . . . . 23 26
6.1 Diffie-Hellman for first CHILD_SA . . . . . . . . . . . . 24 26
6.2 Extended Sequence Numbers (ESN) transform . . . . . . . . 24 26
6.3 Matching ID_IPV4_ADDR and ID_IPV6_ADDR . . . . . . . . . . 24 27
6.4 Relationship of IKEv2 to RFC2401bis . . . . . . . . . . . 25 27
6.5 Reducing the window size . . . . . . . . . . . . . . . . . 25 27
6.6 Minimum size of nonces . . . . . . . . . . . . . . . . . . 25 28
6.7 Initial zero octets on port 4500 . . . . . . . . . . . . . 25 28

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6.8 SPI values in IKE_SA_INIT exchange . . . . . . . . . . . . 26 29
6.9 SPI values for messages outside of an IKE_SA . . . . . . . 27 30
6.10 Protocol ID/SPI fields in Notify payloads . . . . . . . 27 30
6.11 INVALID_IKE_SPI . . . . . . . . . . . . . . . . . . . . 27 30
6.12 Which message should contain INITIAL_CONTACT . . . . . . 28
7. Status of the clarifications . 31
6.13 Message IDs for IKE_SA_INIT messages . . . . . . . . . . 31
6.14 Message IDs for IKE_AUTH messages . . . . . 28

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8. Implementation mistakes . . . . . . 32
6.15 Creating an IKE_SA without a CHILD_SA . . . . . . . . . 32
6.16 Alignment of payloads . . . 30
9. Open issues . . . . . . . . . . . . . . 32
6.17 Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED . . . . . . 32
6.18 Negotiation of NON_FIRST_FRAGMENTS_ALSO . . . . 30 . . . . 33
7. Status of the clarifications . . . . . . . . . . . . . . . . 33
8. Implementation mistakes . . . . . . . . . . . . . . . . . . 35
9. Open issues . . . . . . . . . . . . . . . . . . . . . . . . 35
10. Security considerations . . . . . . . . . . . . . . . . . . 31 36
11. IANA considerations . . . . . . . . . . . . . . . . . . . . 31 36
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 31 36
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 36
13.1 Normative References . . . . . . . . . . . . . . . . . . . 32 36
13.2 Informative References . . . . . . . . . . . . . . . . . . 32 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 34 38
A. Exchanges and payloads . . . . . . . . . . . . . . . . . . . 39
A.1 IKE_SA_INIT exchange . . . . . . . . . . . . . . . . . . . 39
A.2 IKE_AUTH exchange without EAP . . . . . . . . . . . . . . 40
A.3 IKE_AUTH exchange with EAP . . . . . . . . . . . . . . . . 41
A.4 CREATE_CHILD_SA exchange for creating/rekeying CHILD_SAs . 41
A.5 CREATE_CHILD_SA exchange for rekeying the IKE_SA . . . . . 42
A.6 INFORMATIONAL exchange . . . . . . . . . . . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . . 35 43

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1. Introduction

This document clarifies many areas of the IKEv2 specification that
may be difficult to understand to developers not intimately familiar
with the specification and its history. The clarifications in this
document come from the discussion on the IPsec WG mailing list, from
experience in interoperability testing, and from implementation
issues that have been brought to the editors' attention.

Readers are advised that this document is work-in-progress, and may
contain incorrect interpretations. Issues where the clarification is
known to be incomplete, or there is no consensus on what the the
interpretation should be, are marked as such.

IKEv2/IPsec can be used for several different purposes, including
IPsec-based remote access (sometimes called the "road warrior" case),
site-to-site virtual private networks (VPNs), and host-to-host
protection of application traffic. While this document attempts to
consider all of these uses, the remote access scenario has perhaps
received more attention here than the other uses.

This document does not place any requirements on anyone, and does not
use [RFC2119] keywords such as "MUST" and "SHOULD", except in
quotations from the original IKEv2 documents. The requirements are
given in the IKEv2 specification [IKEv2] and IKEv2 cryptographic
algorithms document [IKEv2ALG].

In this document, references to a numbered section (such as "Section
2.15") mean that section in [IKEv2]. References to mailing list
messages refer to the IPsec WG mailing list at ipsec@ietf.org.
Archives of the mailing list can be found at
<http://www.ietf.org/mail-archive/web/ipsec/index.html>.

2. Authentication

2.1 Data included in AUTH payload calculation

Section 2.15 describes how the AUTH payloads are calculated; this
calculation involves values prf(SK_pi,IDi') and prf(SK_pr,IDr'). The
text describes the method in words, but does not give clear
definitions of what is signed or MACed.

The initiator's signed octets can be described as:

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The responder's signed octets can be described as:

2.2 Hash function for RSA signatures

Section 3.8 says that RSA digital signature is "Computed as specified
in section 2.15 using an RSA private key over a PKCS#1 padded hash."

Unlike IKEv1, IKEv2 does not negotiate a hash function for the
IKE_SA. The algorithm for signatures is selected by the signing
party who, in general, may not know beforehand what algorithms the
verifying party supports. Furthermore, [IKEv2ALG] does not say what
algorithms implementations are required or recommended to support.
This clearly has a potential for causing interoperability problems,
since authentication will fail if the signing party selects an
algorithm that is not supported by the verifying party, or not
acceptable according to the verifying party's policy.

This document recommends that all implementations support SHA-1, and
use SHA-1 as the default hash function when generating the
signatures, unless there are good reasons (such as explicit manual
configuration) to believe that the other end supports something else.

Note that unlike IKEv1, IKEv2 uses the PKCS#1 v1.5 [PKCS1v20]
signature encoding method (see next section for details), which
includes the algorithm identifier for the hash algorithm. Thus, when
the verifying party receives the AUTH payload it can determine which
hash function was used.

Other possible choices include, for example, using the hash function

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that was used to sign the certificate. However, this approach
assumes that the recipient's "IKEv2 module" supports the same
algorithms as the "certificate validation module" (which may not be
true, especially if something like [SCVP] is used). Furthermore, not
all CERT payloads types include a signature; and the certificate
could be signed with some other algorithm than RSA.

(References: Magnus Alstrom's mail "RE:", 2005-01-03. Pasi Eronen's
reply, 2005-01-04. Tero Kivinen's reply, 2005-01-04.)

2.3 Encoding method for RSA signatures

Section 3.8 says that the RSA digital signature is "Computed as
specified in section 2.15 using an RSA private key over a PKCS#1
padded hash."

The current version of PKCS#1 (v2.1) [PKCS1v21] defines two different
encoding methods (ways of "padding the hash") for signatures.
However, IKEv2 points to the older PKCS#1 v2.0 [PKCS1v20]. That
version has only one encoding method for signatures
(EMSA-PKCS1-v1_5), (EMSA-PKCS1-
v1_5), and thus there is no ambiguity.

Note that this encoding method is different from the encoding method
used in IKEv1. If future revisions of IKEv2 provide support for
other encoding methods (such as EMSA-PSS), they will be given new
Auth Method numbers.

(References: Pasi Eronen's mail "RE:", 2005-01-04.)

2.4 Identification type for EAP

Section 3.5 defines several different types for identification
payloads, including, e.g., ID_FQDN, ID_RFC822_ADDR, and ID_KEY_ID.
EAP [EAP] does not mandate the use of any particular type of
identifier, but often EAP is used with Network Access Identifiers
(NAIs) defined in [NAI] and [NAIbis]. Although NAIs look a bit like
email addresses (e.g., "joe@example.com"), the syntax is not exactly
the same as the syntax of email address in [RFC822]. This raises the
question of which identification type should be used.

This document recommends that ID_RFC822_ADDR identification type is
used for those NAIs that include the realm component. Therefore,
responder implementations should not attempt to verify that the
contents actually conform to the exact syntax given in [RFC822] or
[RFC2822], but instead should accept any reasonable looking NAI.

For NAIs that do not include the realm component, this document
recommends using the ID_KEY_ID identification type.

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(References: "need your help on this IKEv2/i18n/EAP issue" and "IKEv2
identifier issue with EAP" threads, Aug 2004.)

2.5 Identity for policy lookups when using EAP

When the initiator authentication uses EAP, it is possible that the
contents of the IDi payload is used only for AAA routing purposes and
selecting which EAP method to use. This value may be different from
the identity authenticated by the EAP method (see [EAP], Sections 5.1
and 7.3).

It is important that policy lookups and access control decisions use
the actual authenticated identity. Often the EAP server is
implemented in a separate AAA server that communicates with the IKEv2
responder using, e.g., RADIUS [RADEAP]. In this case, the
authenticated identity has to be sent from the AAA server to the
IKEv2 responder.

(References: Pasi Eronen's mail "RE: Reauthentication in IKEv2",
2004-10-28. "Policy lookups" thread, Oct/Nov 2004. RFC 3748,
Section 7.3.)

2.6 EAP authentication and the AUTH payload

Section 2.16 says that "For EAP methods that create a shared key as a
side effect of authentication, that shared key MUST be used by both
the initiator and responder to generate AUTH payloads in messages 5
and 6 using the syntax for shared secrets specified in section 2.15."

This text should say "messages 7 and 8".

(References: "How to do authentication with EAP" thread, Feb 2005)

2.7 Certificate encoding types

Section 3.6 defines a total of twelve different certificate encoding
types, and continues that "Specific syntax is for some of the
certificate type codes above is not defined in this document."
However, the text does not provide references to other documents that
would contain information about the exact contents and use of those
values.

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Without this information, it is not possible to develop interoperable
implementations. Therefore, this document recommends that the
following certificate encoding values should not be used before new
specifications that specify their use are available.

PKCS #7 wrapped X.509 certificate 1
PGP Certificate 2
DNS Signed Key 3
Kerberos Token 6
SPKI Certificate 9

(Future versions of this document may also contain clarifications
about how these values are to be used.)

This document recommends that most implementations should use only
those values that are "MUST"/"SHOULD" requirements in [IKEv2]; i.e.,
"X.509 Certificate - Signature" (4), "Raw RSA Key" (11), "Hash and
URL of X.509 certificate" (12), and "Hash and URL of X.509 bundle"
(13).

Furthermore, Section 3.7 says that the "Certificate Encoding" field
for the Certificate Request payload uses the same values as for
Certificate payload. However, the contents of the "Certification
Authority" field are defined only for X.509 certificates (presumably
covering at least types 4, 10, 12, and 13). This document recommends
that other values should not be used before new specifications that
specify their use are available.

2.8 Shared key authentication and fixed PRF key size

Section 2.15 says that "If the negotiated prf takes a fixed size key,
the shared secret MUST be of that fixed size". This statement is
correct: the shared secret must be of the correct size. If it is
not, it cannot be used; there is no padding, truncation, or other
processing involved to force it to that correct size.

This requirement means that it is difficult to use these PRFs with
shared key authentication. The authors think this part of the
specification was very poorly thought out, and using PRFs with a
fixed key size is likely to result in interoperability problems.
Thus, we recommend that such PRFs (currently only PRF_AES128_CBC)
should not be used with shared key authentication.

Note that Section 2.13 also contains text that is related to PRFs
with fixed key size: "When the key for the prf function has fixed
length, the data provided as a key is truncated or padded with zeros
as necessary unless exceptional processing is explained following the
formula". However, this text applies only to the prf+ construction,

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so it does not contradict the text in Section 2.15.

(References: Paul Hoffman's mail "Re: ikev2-07: last nits",
2003-05-02. Hugo Krawczyk's reply, 2003-05-12. Thread "Question
about PRFs with fixed size key", Jan 2005.)

2.9 EAP authentication and fixed PRF key size

As described in the previous section, PRFs with a fixed key size
require a shared secret of exactly that size. A strict
interpretation of this text also means that such PRFs are unlikely to
be useful for EAP authentication, since [EAP] specifies that the MSK
is at least 64 octets (512 bits) long, while PRF_AES128_CBC requires
a 128-bit key. It is currently under discussion whether truncation
or padding should be allowed in the EAP case (where the security
implications of truncation are slightly different).

(References: Thread "Question about PRFs with fixed size key", Jan
2005.)

3. Keying and rekeying

3.1 Semantics of the CREATE_CHILD_SA exchange

Section 1.3's organization does not lead

2.10 Matching ID payloads to clear understanding of
what is needed in which environment. certificate contents

In IKEv1, there was some confusion about whether or not the
identities in certificates used to authenticate IKE were required to
match the contents of the ID payloads. There has been some work done
on this in the PKI4IPSEC Working Group, but that work is not finished
at this time. However, Section 3.5 explicitly says that the ID
payload "does not necessarily have to match anything in the CERT
payload".

3. Keying and rekeying

3.1 Semantics of the CREATE_CHILD_SA exchange

Section 1.3's organization does not lead to clear understanding of
what is needed in which environment. The section can be reorganized
with subsections for each use of the CREATE_CHILD_SA exchange
(creating child SAs, rekeying IKE SAs, and rekeying child SAs.)

Further, specific parts of Section 3.1 can be clarified. These
include:

o It is not clear which SA to send in a rekeying a child SA. The
relevant sentence says "If this CREATE_CHILD_SA exchange is
rekeying an existing SA other than the IKE_SA, the leading N
payload of type REKEY_SA MUST identify the SA being rekeyed."
That can be clarified by adding "sender's inbound" before "SA
being rekeyed".

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o The specific method for rekeying an IKE_SA is not described in the
section that describes the rekeying. This is described in Section
2.8. Relevant text from Section 2.8 can be moved here.

o Section 1.3 never mentions the REKEY_SA Notification, but it does
have a mandatory Notification payload when rekeying. The
CREATE_CHILD_SA exchange MUST include a REKEY_SA Notification
payload with an SPI field identifying the SA being rekeyed.

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o The spec is partially wrong about the use of nonces in computing
keys for CHILD_SAs. Section 1.3 says "The nonces from the initial
exchange are used in computing the keys for the CHILD_SA."
However, that is not always true. It is only true for a CHILD_SA
created in the IKE_AUTH exchange. Thus, the sentence can be
ignored because the use of the nonces for computing the keys is
clear in Section 2.17.

The new Section 1.3 with subsections and the above changes might look
like this.

NEW-1.3 The CREATE_CHILD_SA Exchange

The CREATE_CHILD_SA Exchange is used to create new CHILD_SAs and
to rekey both IKE_SAs and CHILD_SAs. This exchange consists of a
single request/response pair, and some of its function was
referred to as a phase 2 exchange in IKEv1. It MAY be initiated
by either end of the IKE_SA after the initial exchanges are
completed.

All messages following the initial exchange are
cryptographically protected using the cryptographic algorithms
and keys negotiated in the first two messages of the IKE
exchange. These subsequent messages use the syntax of the
Encrypted Payload described in section 3.14. All subsequent
messages included an Encrypted Payload, even if they are
referred to in the text as "empty". For both messages in the
CREATE_CHILD_SA, the message following the header is encrypted
and the message including the header is integrity protected
using the cryptographic algorithms negotiated for the IKE_SA.

The CREATE_CHILD_SA is used for rekeying IKE_SAs and
CHILD_SAs. This section describes the first part of rekeying,
the creation of new SAs; Section 2.8 covers the mechanics of
rekeying, including moving traffic from old to new SAs and the
deletion of the old SAs. The two sections must be read together
to understand the entire process of rekeying.

Either endpoint may initiate a CREATE_CHILD_SA exchange, so in

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this section the term initiator refers to the endpoint
initiating this exchange. An implementation MAY refuse all
CREATE_CHILD_SA requests within an IKE_SA.

The CREATE_CHILD_SA request MAY optionally contain a KE payload
for an additional Diffie-Hellman exchange to enable stronger
guarantees of forward secrecy for the CHILD_SA. The keying
material for the CHILD_SA is a function of SK_d established
during the establishment of the IKE_SA, the nonces exchanged

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during the CREATE_CHILD_SA exchange, and the Diffie-Hellman
value (if KE payloads are included in the CREATE_CHILD_SA
exchange).

If a CREATE_CHILD_SA exchange includes a KEi payload, at least
one of the SA offers MUST include the Diffie-Hellman group of
the KEi. The Diffie-Hellman group of the KEi MUST be an element
of the group the initiator expects the responder to accept
(additional Diffie-Hellman groups can be proposed). If the
responder rejects the Diffie-Hellman group of the KEi payload,
the responder MUST reject the request and indicate its preferred
Diffie-Hellman group in the INVALID_KE_PAYLOAD Notification
payload. In the case of such a rejection, the CREATE_CHILD_SA
exchange fails, and the initiator SHOULD retry the exchange with
a Diffie-Hellman proposal and KEi in the group that the
responder gave in the INVALID_KE_PAYLOAD.

NEW-1.3.1 Creating New CHILD_SAs with the CREATE_CHILD_SA Exchange

A CHILD_SA may be created by sending a CREATE_CHILD_SA request.
The CREATE_CHILD_SA request for creating a new CHILD_SA is:

Initiator Responder
----------- -----------
HDR, SK {SA, Ni, [KEi],
TSi, TSr} -->

The initiator sends SA offer(s) in the SA payload, a nonce in
the Ni payload, optionally a Diffie-Hellman value in the KEi
payload, and the proposed traffic selectors for the proposed
CHILD_SA in the TSi and TSr payloads.

The CREATE_CHILD_SA response for creating a new CHILD_SA is:

<-- HDR, SK {SA, Nr, [KEr],
TSi, TSr}

The responder replies (using the same Message ID to respond)
with the accepted offer in an SA payload, and a Diffie-Hellman

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value in the KEr payload if KEi was included in the request and
the selected cryptographic suite includes that group.

The traffic selectors for traffic to be sent on that SA are
specified in the TS payloads in the response, which may be a
subset of what the initiator of the CHILD_SA proposed.

NEW-1.3.2 Rekeying IKE_SAs with the CREATE_CHILD_SA Exchange

The CREATE_CHILD_SA request for rekeying an IKE_SA is:

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Initiator Responder
----------- -----------
HDR, SK {SA, Ni, [KEi]} KEi} -->

The initiator sends SA offer(s) in the SA payload, a nonce in
the Ni payload, and optionally a Diffie-Hellman value in the KEi payload.
New initiator and responder SPIs are supplied in the SPI fields.

The CREATE_CHILD_SA response for rekeying an IKE_SA is:

<-- HDR, SK {SA, Nr, [KEr]} KEr}

The responder replies (using the same Message ID to respond)
with the accepted offer in an SA payload, and a Diffie-Hellman
value in the KEr payload if KEi was included in the request and the selected cryptographic suite
includes that group.

The new IKE_SA has its message counters set to 0, regardless of
what they were in the earlier IKE_SA. The window size starts at
1 for any new IKE_SA.

KEi and KEr are required for rekeying an IKE_SA.

NEW-1.3.3 Rekeying CHILD_SAs with the CREATE_CHILD_SA Exchange

The CREATE_CHILD_SA request for rekeying a CHILD_SA is:

Initiator Responder
----------- -----------
HDR, SK {N, SA, Ni, [KEi],
TSi, TSr} -->

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included and MUST identify give the SPI (as they would be expected in
the sender's headers of inbound SA packets) of the SAs being rekeyed.

The CREATE_CHILD_SA response for rekeying a CHILD_SA is:

<-- HDR, SK {SA, Nr, [KEr],
TSi, TSr}

The responder replies (using the same Message ID to respond)
with the accepted offer in an SA payload, and a Diffie-Hellman
value in the KEr payload if KEi was included in the request and
the selected cryptographic suite includes that group.

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The traffic selectors for traffic to be sent on that SA are
specified in the TS payloadsin payloads in the response, which may be a
subset of what the initiator of the CHILD_SA proposed.

3.2 Rekeying the IKE_SA vs. reauthentication

Rekeying the IKE_SA and reauthentication are different concepts in
IKEv2. Rekeying the IKE_SA establishes new keys for the IKE_SA and
resets the Message ID counters, but it does not authenticate the
parties again (no AUTH or EAP payloads are involved).

While rekeying the IKE_SA may be important in some environments,
reauthentication (the verification that the parties still have access
to the long-term credentials) is often more important.

IKEv2 does not have any special support for reauthentication.
Reauthentication is done by creating a new IKE_SA from scratch (using
IKE_SA_INIT/IKE_AUTH exchanges, without any REKEY_SA notify
payloads), creating new CHILD_SAs within the new IKE_SA (without
REKEY_SA notify payloads), and finally deleting the old IKE_SA (which
deletes the old CHILD_SAs as well).

This means that reauthentication also establishes new keys for the
IKE_SA and CHILD_SAs. Therefore, while rekeying can be performed
more often than reauthentication, the situation where "authentication
lifetime" is shorter than "key lifetime" does not make sense.

While creation of a new IKE_SA can be initiated by either party
(initiator or responder in the original IKE_SA), the use of EAP
authentication and/or configuration payloads means in practice that
reauthentication has to be initiated by the same party as the
original IKE_SA. IKEv2 does not currently allow the responder to
request reauthentication in this case; however, there is ongoing work
to add this functionality [ReAuth].

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(References: "Reauthentication in IKEv2" thread, Oct/Nov 2004.)

3.3 SPIs when rekeying the IKE_SA

Section 2.18 says that "New initiator and responder SPIs are supplied
in the SPI fields". This refers to the SPI fields in the Proposal
structures inside the Security Association (SA) payloads, not the SPI
fields in the IKE header.

(References: Tom Stiemerling's mail "Rekey IKE SA", 2005-01-24.
Geoffrey Huang's reply, 2005-01-24.)

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3.4 SPI when rekeying a CHILD_SA

Section 3.10.1 says that in REKEY_SA notifications, "The SPI field
identifies the SA being rekeyed."

Since CHILD_SAs always exist in pairs, there are two different SPIs.
The SPI placed in the REKEY_SA notification is the SPI the exchange
initiator would expect in inbound ESP or AH packets (just as in
Delete payloads).

3.5 Changing PRFs when rekeying the IKE_SA

When rekeying the IKE_SA, Section 2.18 says that "SKEYSEED for the
new IKE_SA is computed using SK_d from the existing IKE_SA as
follows:

SKEYSEED = prf(SK_d (old), [g^ir (new)] | Ni | Nr)"

If the old and new IKE_SA selected a different PRF, it is not clear
which PRF should be used.

Regardless of which is the correct answer, it works poorly if the new
IKE_SA's PRF has a fixed key size. If the new PRF is also used to
calculate SKEYSEED, then SK_d may not be of the correct size. And if
SKEYSEED is calculated using the old PRF, then it may not be of the
correct size for the new PRF.

Although it is not yet clear which is the correct answer, this
supports our opinion earlier in the document that the use of PRFs
with a fixed key size is a bad idea.

3.6 Deleting vs. closing SAs

It is not clear that SAs must be actively deleted. The text
sometimes says that SAs are "closed" when it means that the SAs are
actively deleted. Section 1.4 says "ESP and AH SAs always exist in

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pairs, with one SA in each direction. When an SA is closed, both
members of the pair MUST be closed." It is important to note that
SAs that are closed need to be actively deleted with DELETE payloads.

4. Traffic selectors

4.1 Semantics of complex traffic selector payloads

As described in

3.7 Deleting a CHILD_SA pair

Section 3.13, 1.4 describes how to delete SA pairs using the TSi/TSr payloads can include Informational
exchange: "To delete an SA, an INFORMATIONAL Exchange with one or
more individual traffic selectors.

There delete payloads is no requirement that TSi and TSr contain sent listing the same number of
individual traffic selectors. Thus, SPIs (as they are interpreted as follows:
a packet matches a given TSi/TSr if it matches at least one of the
individual selectors would be
expected in TSi, and at least one the headers of inbound packets) of the individual
selectors in TSr.

For instance, SAs to be deleted.
The recipient MUST close the following traffic selectors:

TSi = ((17, 100, 192.0.1.66-192.0.1.66),
(17, 200, 192.0.1.66-192.0.1.66))
TSr = ((17, 300, 0.0.0.0-255.255.255.255),
(17, 400, 0.0.0.0-255.255.255.255))

would match UDP packets from 192.0.1.66 to anywhere, with any of the
four combinations of source/destination ports (100,300), (100,400),
(200,300), and (200, 400).

This implies that designated SAs."

The "one or more delete payloads" phrase has caused some types of policies may require several CHILD_SA
pairs. For instance, a policy matching only source/destination ports
(100,300) and (200,400), but not confusion.
You never send delete payloads for the other two combinations, cannot
be negotiated as sides of an SA in a single CHILD_SA pair using IKEv2.

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(References: "IKEv2 Traffic Selectors?" thread, Feb 2005.)

4.2 ICMP type/code in traffic selector payloads

The traffic selector types 7 and 8 can also refer
message. If you have many SAs to ICMP type and
code fields. As described in Section 3.13.1, "For the ICMP protocol, delete at the two one octet fields Type and Code are treated same time (such as a single 16 bit
integer (with Type in
the most significant eight bits and Code nested example given in the
least significant eight bits) port number that paragraph), you include delete
payloads for the purposes of
filtering based on this field."

This encoding is quite clear. However, as both TSi and TSr are
always present, together they have two "start port" fields (one in
TSi and one inbound half or each SA in TSr) and two "end port" fields. your Informational
exchange.

3.8 Deleting an IKE_SA

Since ICMP messages
only have a single type/code field (instead of separate
source/destination ports, like TCP and UDP), there IKE_SAs do not exist in pairs, it is some room for
confusion.

One sensible interpretation would be that in case of ICMP, the "start
port" fields in TSi and TSr must always be equal, and likewise for
the "end port" fields.

4.3 Mobility header in traffic selector payloads

Traffic selectors can use IP Protocol ID 135 to match not totally clear what the IPv6
mobility header [MIPv6]. However,
response message should contain when the IKEv2 specification does not
define how to represent request deleted the "MH Type" field in traffic selectors.

At some point, it was expected IKE_SA.

Since there is no information that this will needs to be defined in a
separate document later. However, [RFC2401bis] says sent to the other side
(except that "For IKE, the IPv6 mobility header message type (MH type) is placed in request was received), an empty Informational
response seems like the most
significant eight bits of the 16 bit local "port" selector." logical choice.

(References: Tero Kivinen's mail "Issue #86: Add IPv6 mobility header
message type as selector", 2003-10-14.)

4.4 Narrowing "Question about delete IKE SA" thread, May 2005.)

3.9 Who is the traffic selectors

Section 2.9 describes how traffic selectors are negotiated when
creating a CHILD_SA. A more concise summary original initiator of IKE_SA

In the narrowing process
is presented below.

o If IKEv2 document, "initiator" refers to the responder's policy does not allow any part of party who initiated
the traffic
covered by TSi/TSr, it responds with TS_UNACCEPTABLE.

o If exchange being described, and "original initiator" refers to the responder's policy allows
party who initiated the entire set of traffic covered
by TSi/TSr, no narrowing whole IKE_SA. However, there is necessary, and some
potential for confusion because the responder IKE_SA can
return the same TSi/TSr values.

Eronen & be rekeyed by either
party.

To clear up this confusion, we propose that "original initiator"
always refers to the party who initiated the exchange which resulted
in the current IKE_SA. In other words, if the the "original
responder" starts rekeying the IKE_SA, that party becomes the
"original initiator" of the new IKE_SA.

(References: Paul Hoffman's mail "Original initiator in IKEv2", 2005-
04-21.)

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o Otherwise, narrowing is needed. If the responder's policy allows
all traffic covered by TSi[1]/TSr[1] (the first traffic

4. Traffic selectors

4.1 Semantics of complex traffic selector payloads

As described in TSi/TSr) but not entire TSi/TSr, Section 3.13, the responder narrows to an
acceptable subset of TSi/TSr payloads can include one or
more individual traffic selectors.

There is no requirement that includes TSi[1]/TSr[1].

o If TSi and TSr contain the responder's policy does not allow all traffic covered by
TSi[1]/TSr[1], but does allow some parts same number of TSi/TSr,
individual traffic selectors. Thus, they are interpreted as follows:
a packet matches a given TSi/TSr if it narrows to
an acceptable subset matches at least one of TSi/TSr.

In the last two cases, there may be several subsets that are
acceptable (but their union is not);
individual selectors in this case, the responder
arbitrarily chooses TSi, and at least one of them, and includes ADDITIONAL_TS_POSSIBLE
notification the individual
selectors in TSr.

For instance, the response.

4.5 SINGLE_PAIR_REQUIRED

The description following traffic selectors:

TSi = ((17, 100, 192.0.1.66-192.0.1.66),
(17, 200, 192.0.1.66-192.0.1.66))
TSr = ((17, 300, 0.0.0.0-255.255.255.255),
(17, 400, 0.0.0.0-255.255.255.255))

would match UDP packets from 192.0.1.66 to anywhere, with any of the SINGLE_PAIR_REQUIRED notify payload in
Sections 2.9
four combinations of source/destination ports (100,300), (100,400),
(200,300), and 3.10.1 is not fully consistent.

We do not attempt to describe this payload in this document either,
since it is expected (200, 400).

This implies that most implementations will not have some types of policies
that may require separate SAs for each address pair.

Thus, if several CHILD_SA
pairs. For instance, a policy matching only some part (or parts) of the TSi/TSr proposed by the
initiator is (are) acceptable to the responder, most responders
should simply narrow TSi/TSr to an acceptable subset (as described in source/destination ports
(100,300) and (200,400), but not the last other two paragraphs of Section 2.9), rather than use
SINGLE_PAIR_REQUIRED.

4.6 combinations, cannot
be negotiated as a single CHILD_SA pair using IKEv2.

(References: "IKEv2 Traffic selectors violating own policy

Section 2.9 describes Selectors?" thread, Feb 2005.)

4.2 ICMP type/code in traffic selector negotiation payloads

The traffic selector types 7 and 8 can also refer to ICMP type and
code fields. As described in great detail.
One aspect of this negotiation that may need some clarification is
that when creating Section 3.13.1, "For the ICMP protocol,
the two one octet fields Type and Code are treated as a new SA, single 16 bit
integer (with Type in the initiator should not propose traffic
selectors that violate its own policy. If most significant eight bits and Code in the
least significant eight bits) port number for the purposes of
filtering based on this rule is not followed,
valid traffic may be dropped. field."

This encoding is best illustrated by an example. Suppose that host A has a
policy whose effect is that traffic to 192.0.1.66 is sent via host B
encrypted using AES, quite clear. However, as both TSi and traffic to all other hosts TSr are
always present, together they have two "start port" fields (one in 192.0.1.0/24
is also sent via B, but must use 3DES. Suppose also that host B
accepts any combination of AES
TSi and 3DES.

If host A now proposes an SA that uses 3DES, one in TSr) and includes TSr
containing (192.0.1.0-192.0.1.0.255), this will be accepted by host
B. Now, host B can also use this SA to send traffic from 192.0.1.66,
but those packets will be dropped by A since it requires the use of
AES for those traffic. Even if host A creates a new SA two "end port" fields. Since ICMP messages
only have a single type/code field (instead of separate source/
destination ports, like TCP and UDP), there is some room for
confusion.

One sensible interpretation would be that in case of ICMP, the "start

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192.0.1.66 that uses AES, host B may freely continue to use the first
SA for the traffic. In this situation, when proposing the SA, host A
should have followed its own policy,

port" fields in TSi and included a TSr containing
((192.0.1.0-192.0.1.65),(192.0.1.67-192.0.1.255)) instead.

In general, if (1) the initiator makes a proposal "for traffic X
(TSi/TSr), do SA", must always be equal, and (2) likewise for some subset X' of X, the initiator
does not actually accept traffic X' with SA, and (3)
the initiator
would be willing to accept traffic X' with some SA' (!=SAi), valid "end port" fields.

4.3 Mobility header in traffic selector payloads

Traffic selectors can be unnecessarily dropped since the responder can apply
either SA or SA' use IP Protocol ID 135 to traffic X'.

(References: "Question about "narrowing" ..." thread, Feb 2005.
"IKEv2 needs a "policy usage mode"..." thread, Feb 2005. "IKEv2
Traffic Selectors?" thread, Feb 2005. "IKEv2 traffic selector
negotiation examples", 2004-08-08.)

5. Configuration payloads

5.1 Length of configuration attribute type field

In Section 3.15.1, Figure 23 shows that match the length of IPv6
mobility header [MIPv6]. However, the "Attribute IKEv2 specification does not
define how to represent the "MH Type" field is 15 bits, while the text below the figure in traffic selectors.

At some point, it was expected that this will be defined in a
separate document later. However, [RFC2401bis] says that "For IKE,
the
length is 7 bits.

The figure IPv6 mobility header message type (MH type) is correct, placed in the field is 15 bits. most
significant eight bits of the 16 bit local "port" selector."

(References: Tero Kivinen's mail "Comments to "Issue #86: Add IPv6 mobility header
message type as selector", 2003-10-14.)

4.4 Narrowing the
draft-ietf-ipsec-ikev2-11.txt", 2003-11-09. Yoav Nir's mail "Will
ikev2-16 be traffic selectors

Section 2.9 describes how traffic selectors are negotiated when
creating a CHILD_SA. A more concise summary of the charm?", 2004-09-23. Charlie Kaufman's
mail"draft-ietf-ipsec-ikev2-17.txt", 2004-10-04. It narrowing process
is expected that
this issue will be fixed during the "Authors' 48 hours" before presented below.

o If the
RFC is published.)

5.2 Requesting responder's policy does not allow any INTERNAL_IP4/IP6_ADDRESS

When describing part of the INTERNAL_IP4/IP6_ADDRESS attributes, Section
3.15.1 says that "In a request message, traffic
covered by TSi/TSr, it responds with TS_UNACCEPTABLE.

o If the address specified is a
requested address (or zero if responder's policy allows the entire set of traffic covered
by TSi/TSr, no specific address is requested)".
The question here narrowing is that does "zero" mean an address "0.0.0.0" or a
zero length string?

Earlier, necessary, and the responder can
return the same section also says that "If an attribute TSi/TSr values.

o Otherwise, narrowing is needed. If the responder's policy allows
all traffic covered by TSi[1]/TSr[1] (the first traffic selectors
in TSi/TSr) but not entire TSi/TSr, the
CFG_REQUEST Configuration Payload is responder narrows to an
acceptable subset of TSi/TSr that includes TSi[1]/TSr[1].

o If the responder's policy does not zero length allow all traffic covered by
TSi[1]/TSr[1], but does allow some parts of TSi/TSr, it is taken as a
suggestion for narrows to
an acceptable subset of TSi/TSr.

In the last two cases, there may be several subsets that attribute". Also, are
acceptable (but their union is not); in this case, the table responder
arbitrarily chooses one of configuration
attributes shows that them, and includes ADDITIONAL_TS_POSSIBLE
notification in the length response.

4.5 SINGLE_PAIR_REQUIRED

The description of INTERNAL_IP4_ADDRESS is either "0
or 4 octets", the SINGLE_PAIR_REQUIRED notify payload in
Sections 2.9 and likewise, INTERNAL_IP6_ADDRESS 3.10.1 is either "0 or 17
octets". not fully consistent.

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Thus, if the client does not request a specific address, it includes
a zero-length INTERNAL_IP4/IP6_ADDRESS attribute,

We do not an attribute
containing an all-zeroes address. The example attempt to describe this payload in 2.19 is thus
incorrect, this document either,
since it shows the attribute as
"INTERNAL_ADDRESS(0.0.0.0)".

However, since the value is only a suggestion, expected that most implementations are
recommended to ignore suggestions they do not accept; or in other
words, treat the same way a zero-length INTERNAL_IP4_ADDRESS,
"0.0.0.0", and any other addresses the implementation does will not
recognize as a reasonable suggestion.

5.3 INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET

Section 3.15.1 describes the INTERNAL_IP4_SUBNET as "The protected
sub-networks have policies
that this edge-device protects. This attribute is made
up require separate SAs for each address pair.

Thus, if only some part (or parts) of two fields; the first being an IP address and TSi/TSr proposed by the second being
a netmask. Multiple sub-networks MAY be requested. The responder
MAY respond with zero or more sub-network attributes."
INTERNAL_IP6_SUBNET is defined in a similar manner.

This raises two questions: first, since this information
initiator is usually
included in (are) acceptable to the TSr payload, what functionality does this attribute
add? And second, what does this attribute mean responder, most responders
should simply narrow TSi/TSr to an acceptable subset (as described in CFG_REQUESTs?

For
the first question, there seem to be last two sensible
interpretations. Clearly TSr (in IKE_AUTH or CREATE_CHILD_SA
response) indicates which subnets are accessible through the SA that
was just created.

The first interpretation paragraphs of Section 2.9), rather than use
SINGLE_PAIR_REQUIRED.

4.6 Traffic selectors violating own policy

Section 2.9 describes traffic selector negotiation in great detail.
One aspect of the INTERNAL_IP4/6_SUBNET attributes is
that they indicate additional subnets that can be reached through this gateway, but negotiation that may need some clarification is
that when creating a separate SA. According to this
interpretation, new SA, the INTERNAL_IP4/6_SUBNET attributes are useful
mainly when they contain addresses initiator should not included in TSr.

The second interpretation is propose traffic
selectors that the INTERNAL_IP4/6_SUBNET
attributes express the gateway's policy about what violate its own policy. If this rule is not followed,
valid traffic should may be
sent through the gateway. The client can choose whether other
traffic (covered dropped.

This is best illustrated by TSr, but not in INTERNAL_IP4/6_SUBNET) an example. Suppose that host A has a
policy whose effect is sent
through the gateway or directly the destination. According to this
interpretation, the attributes are useful mainly when TSr contains
addresses not included in the INTERNAL_IP4/6_SUBNET attributes.

These two interpretations are not totally incompatible: in both
cases, they suggest that traffic to the addresses listed 192.0.1.66 is sent via host B
encrypted using AES, and traffic to all other hosts in the
INTERNAL_IP4/6_SUBNET attributes should be 192.0.1.0/24
is also sent via this gateway
(and, B, but must use 3DES. Suppose also that host B
accepts any combination of course, the packets have to AES and 3DES.

If host A now proposes an SA that uses 3DES, and includes TSr
containing (192.0.1.0-192.0.1.0.255), this will be sent over some accepted by host
B. Now, host B can also use this SA whose

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but those packets will be dropped by A couple since it requires the use of examples are given below. For instance,
AES for those traffic. Even if there are two
subnets, 192.0.1.0/26 and 192.0.2.0/24, and host A creates a new SA only for
192.0.1.66 that uses AES, host B may freely continue to use the client's request
contains first
SA for the following:

CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65536, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65536, 0.0.0.0-255.255.255.255)

Then a valid response could be the following (in which TSr and
INTERNAL_IP4_SUBNET contain the same information):

CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(192.0.1.234)
INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65536, 192.0.1.234-192.0.1.234)
TSr = ((0, 0-65536, 192.0.1.0-192.0.1.63),
(0, 0-65536, 192.0.2.0-192.0.2.255)) traffic. In these cases, this situation, when proposing the INTERNAL_IP4_SUBNET does not really carry any
useful information. Another possible reply would SA, host A
should have been this:

This would mean that the client can send all followed its traffic through the
gateway, but the gateway does not mind if the client sends traffic
not own policy, and included by INTERNAL_IP4_SUBNET directly to the destination
(without going through the gateway).

A different situation arises a TSr containing
((192.0.1.0-192.0.1.65),(192.0.1.67-192.0.1.255)) instead.

In general, if (1) the gateway has initiator makes a policy that
requires the proposal "for traffic X
(TSi/TSr), do SA", and (2) for some subset X' of X, the two subnets to be carried in separate
SAs. Then a response like this initiator
does not actually accept traffic X' with SA, and (3) the initiator
would indicate be willing to accept traffic X' with some SA' (!=SAi), valid
traffic can be unnecessarily dropped since the client that if
it wants access responder can apply
either SA or SA' to the second subnet, it traffic X'.

(References: "Question about "narrowing" ..." thread, Feb 2005.
"IKEv2 needs to create a separate
SA:

CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(192.0.1.234)
INTERNAL_IP4_SUBNET(192.0.1.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65536, 192.0.1.234-192.0.1.234) "policy usage mode"..." thread, Feb 2005. "IKEv2
Traffic Selectors?" thread, Feb 2005. "IKEv2 traffic selector
negotiation examples", 2004-08-08.)

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5. Configuration payloads

5.1 Length of configuration attribute type field

In Section 3.15.1, Figure 23 shows that the length of the "Attribute
Type" field is 15 bits, while the text below the figure says the
length is 7 bits.

The figure is correct, the field is 15 bits.

(References: Tero Kivinen's mail "Comments to the
draft-ietf-ipsec-ikev2-11.txt", 2003-11-09. Yoav Nir's mail "Will
ikev2-16 be the charm?", 2004-09-23. Charlie Kaufman's
mail"draft-ietf-ipsec-ikev2-17.txt", 2004-10-04. It is expected that
this issue will be fixed during the "Authors' 48 hours" before the
RFC is published.)

5.2 Requesting any INTERNAL_IP4/IP6_ADDRESS

When describing the INTERNAL_IP4/IP6_ADDRESS attributes, Section
3.15.1 says that "In a request message, the address specified is a
requested address (or zero if no specific address is requested)".
The question here is that does "zero" mean an address "0.0.0.0" or a
zero length string?

Earlier, the same section also says that "If an attribute in the
CFG_REQUEST Configuration Payload is not zero length it is taken as a
suggestion for that attribute". Also, the table of configuration
attributes shows that the length of INTERNAL_IP4_ADDRESS is either "0
or 4 octets", and likewise, INTERNAL_IP6_ADDRESS is either "0 or 17
octets".

Thus, if the client does not request a specific address, it includes
a zero-length INTERNAL_IP4/IP6_ADDRESS attribute, not an attribute
containing an all-zeroes address. The example in 2.19 is thus
incorrect, since it shows the attribute as
"INTERNAL_ADDRESS(0.0.0.0)".

However, since the value is only a suggestion, implementations are
recommended to ignore suggestions they do not accept; or in other
words, treat the same way a zero-length INTERNAL_IP4_ADDRESS,
"0.0.0.0", and any other addresses the implementation does not
recognize as a reasonable suggestion.

5.3 INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET

Section 3.15.1 describes the INTERNAL_IP4_SUBNET as "The protected
sub-networks that this edge-device protects. This attribute is made

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up of two fields; the first being an IP address and the second being
a netmask. Multiple sub-networks MAY be requested. The responder
MAY respond with zero or more sub-network attributes."
INTERNAL_IP6_SUBNET is defined in a similar manner.

This raises two questions: first, since this information is usually
included in the TSr payload, what functionality does this attribute
add? And second, what does this attribute mean in CFG_REQUESTs?

For the first question, there seem to be two sensible
interpretations. Clearly TSr (in IKE_AUTH or CREATE_CHILD_SA
response) indicates which subnets are accessible through the SA that
was just created.

The first interpretation of the INTERNAL_IP4/6_SUBNET attributes is
that they indicate additional subnets that can be reached through
this gateway, but need a separate SA. According to this
interpretation, the INTERNAL_IP4/6_SUBNET attributes are useful
mainly when they contain addresses not included in TSr.

The second interpretation is that the INTERNAL_IP4/6_SUBNET
attributes express the gateway's policy about what traffic should be
sent through the gateway. The client can choose whether other
traffic (covered by TSr, but not in INTERNAL_IP4/6_SUBNET) is sent
through the gateway or directly the destination. According to this
interpretation, the attributes are useful mainly when TSr contains
addresses not included in the INTERNAL_IP4/6_SUBNET attributes.

These two interpretations are not totally incompatible: in both
cases, they suggest that traffic to the addresses listed in the
INTERNAL_IP4/6_SUBNET attributes should be sent via this gateway
(and, of course, the packets have to be sent over some SA whose
traffic selectors cover the address in question).

A couple of examples are given below. For instance, if there are two
subnets, 192.0.1.0/26 and 192.0.2.0/24, and the client's request
contains the following:

CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65536, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65536, 0.0.0.0-255.255.255.255)

Then a valid response could be the following (in which TSr and
INTERNAL_IP4_SUBNET contain the same information):

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In these cases, the INTERNAL_IP4_SUBNET does not really carry any
useful information. Another possible reply would have been this:

This would mean that the client can send all its traffic through the
gateway, but the gateway does not mind if the client sends traffic
not included by INTERNAL_IP4_SUBNET directly to the destination
(without going through the gateway).

A different situation arises if the gateway has a policy that
requires the traffic for the two subnets to be carried in separate
SAs. Then a response like this would indicate to the client that if
it wants access to the second subnet, it needs to create a separate
SA:

INTERNAL_IP4_SUBNET can also be useful if the client's TSr included
only part of the address space. For instance, if the client requests
the following:

CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65536, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65536, 192.0.2.155-192.0.2.155)

Then the gateway's reply could be this:

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It is less clear what the attributes mean in CFG_REQUESTs, and
whether other lengths than zero make sense in this situation (but for
INTERNAL_IP6_SUBNET, zero length is not allowed at all!). Currently
this document recommends that implementations should not include
INTERNAL_IP4_SUBNET or INTERNAL_IP6_SUBNET attributes in
CFG_REQUESTs.

For the IPv4 case, this document recommends using only netmasks
consisting of some amount of "1" bits followed by "0" bits; for
instance, "255.0.255.0" would not be a valid netmask for
INTERNAL_IP4_SUBNET.

(References: Tero Kivinen's mail "Intent of couple of attributes in
Configuration Payload in IKEv2?", 2004-11-19. Srinivasa Rao
Addepalli's mail "INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET in
IKEv2", 2004-09-10. Yoav Nir's mail "Re: New I-D: IKEv2
Clarifications and Implementation Guidelines", 2005-02-07.)

5.4 INTERNAL_IP4_NETMASK

Section 3.15.1 defines the INTERNAL_IP4_NETMASK attribute, and says
that "The internal network's netmask. Only one netmask is allowed in
the request and reply messages (e.g., 255.255.255.0) and it MUST be
used only with an INTERNAL_IP4_ADDRESS attribute".

However, it is not clear what exactly this attribute means, as the
concept of "netmask" is not very well defined for point-to-point
links (unlike multi-access links, where it means "you can reach hosts
inside this netmask directly using layer 2, instead of sending
packets via a router").

One possible interpretation would be that the host is given a whole
block of IP addresses instead of a single address. This is also what
Framed-IP-Netmask does in [RADIUS] and the IPCP "subnet mask"
extension does in PPP [IPCPSubnet]. This interpretation would also
work nicely with IPv6 (see the following section).

However, one IKEv2 guru assured the authors that this interpretation
is not correct. Section 3.15.1 also says that multiple addresses are
assigned using multiple INTERNAL_IP4_ADDRESS attributes.

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TSr = (0, 0-65536, 192.0.1.0-192.0.1.63)

Currently, this document's interpretation is the following:

o INTERNAL_IP4_NETMASK in a CFG_REPLY means exactly the same thing
as INTERNAL_IP4_SUBNET can also be useful if containing the client's TSr included
only part same information (see the
previous section for description of INTERNAL_IP4_SUBNET).

o INTERNAL_IP4_NETMASK does not make sense for CFG_REQUESTs, and the address space. For
example in Section 2.19 is incorrect in this sense. (Another
interpretation would be that by sending, for instance, if the
combination of INTERNAL_IP4_ADDRESS(192.0.2.0) and
INTERNAL_IP4_NETMASK(255.255.255.0), the client requests is asking to be
assigned one IP address from the following:

CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65536, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65536, 192.0.2.155-192.0.2.155)

Then network 192.0.2.0/24. However,
this interpretation is not supported by the gateway's reply could be this:

It IKEv2 spec.)

This interpretation is less clear what not yet settled; and it would imply that the attributes mean in CFG_REQUESTs,
whole attribute is totally unnecessary.

Yet another possible interpretation would be that
INTERNAL_IP4_NETMASK indicates a broadcast address, meaning that if a
client sends a packet to this address, the gateway will decrypt it
and
whether send copies to all other lengths than zero make sense VPN clients in this situation (but for
INTERNAL_IP6_SUBNET, zero length that address range.
However, no implementation is not allowed at all!). Currently known to do this, and there is nothing
in the IKEv2 spec that would support this document recommends interpretation.

Fortunately, Section 4 clearly says that implementations should a minimal implementation
does not need to include
INTERNAL_IP4_SUBNET or INTERNAL_IP6_SUBNET attributes in
CFG_REQUESTs.

For understand the IPv4 case, INTERNAL_IP4_NETMASK
attribute, and thus this document recommends using only netmasks
consisting of some amount of "1" bits followed by "0" bits; for
instance, "255.0.255.0" would that implementations
should not be a valid netmask for
INTERNAL_IP4_SUBNET. use the INTERNAL_IP4_NETMASK attribute at all.

(References: Tero Kivinen's mail "Intent of couple of attributes in
Configuration Payload in IKEv2?", 2004-11-19. Srinivasa Rao
Addepalli's Charlie Kaufman's mail "INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET in "RE: Proposed Last Call based
revisions to IKEv2", 2004-09-10. 2004-05-27. Email discussion with Tero Kivinen,
Jan 2005. Yoav Nir's mail "Re: New I-D: IKEv2 Clarifications and
Implementation Guidelines", 2005-02-07.)

5.4 INTERNAL_IP4_NETMASK

However, it is not clear what exactly this attribute means, as the
concept of "netmask" is not very well defined

5.5 Configuration payloads for point-to-point
links (unlike multi-access links, where it means "you can reach hosts

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IKEv2 Clarifications March 2005

inside this netmask directly using layer 2, instead of sending
packets via a router").

One possible interpretation would be that the host is given a whole
block of IP addresses instead of a single address. This is also what
Framed-IP-Netmask does in [RADIUS] defines configuration payloads for IPv6. However, they
are based on the corresponding IPv4 payloads, and do not fully follow
the IPCP "subnet mask"
extension does in PPP [IPCPSubnet]. This interpretation would also
work nicely with "normal IPv6 (see the following section).

However, one way of doing things".

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A client can be assigned an IPv6 address using the authors that this interpretation
is not correct. Section 3.15.1 also says
INTERNAL_IP6_ADDRESS configuration payload. Presumably, the idea was
that multiple addresses a minimal exchange would look something like this:

CP(CFG_REQUEST) =
INTERNAL_IP6_ADDRESS()
INTERNAL_IP6_DNS()
TSi = (0, 0-65536, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65536, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)

CP(CFG_REPLY) =
INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5/?)
INTERNAL_IP6_DNS(2001:DB8:99:88:77:66:55:44)
TSi = (0, 0-65536, 2001:DB8:0:1:2:3:4:5 - 2001:DB8:0:1:2:3:4:5)
TSr = (0, 0-65536, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)

In particular, IPv6 stateless autoconfiguration or router
advertisement messages are
assigned using multiple INTERNAL_IP4_ADDRESS attributes.

Currently, not used; neither is neighbor discovery.

While this document's interpretation approach is the following:

o INTERNAL_IP4_NETMASK reasonably simple, it has some limitations:
IPsec tunnels configured using IKEv2 are not fully-featured
"interfaces" in a CFG_REPLY means exactly the same thing
as INTERNAL_IP4_SUBNET containing the same information (see the
previous section for description of INTERNAL_IP4_SUBNET).

o INTERNAL_IP4_NETMASK does IPv6 addressing architecture [IPv6Addr] sense.
In particular, they do not make sense for CFG_REQUESTs, necessarily have link-local addresses, and
this may complicate the
example use of protocols that assume them, such as
[MLDv2]. (Whether they are called "interfaces" in Section 2.19 some particular
operating system is incorrect in a different issue.)

(References: "VPN remote host configuration IPv6 ?" thread, May
2004.)

5.6 INTERNAL_IP6_ADDRESS prefix length

Earlier versions of the IKEv2 draft had an INTERNAL_IP6_NETMASK
attribute corresponding to INTERNAL_IP4_NETMASK, but this sense. (Another
interpretation was deleted
when the prefix length field was added to the INTERNAL_IP6_ADDRESS
attribute. Thus, it seems logical to assume that their purpose would
be similar; however, this is far from obvious.

The draft quite clearly says that by sending, for instance, the
combination of INTERNAL_IP4_ADDRESS(192.0.2.0) and
INTERNAL_IP4_NETMASK(255.255.255.0), the client is asking to be assigned one IP an IPv6
address from using the network 192.0.2.0/24. INTERNAL_IP6_ADDRESS attribute. However,
this interpretation as with
the netmask in IPv4, it is not supported by clear what the IKEv2 spec.)

This prefix length here
means.

Again, one possible interpretation is not yet settled; and it would imply that a prefix length smaller
than 128 in a CFG_REPLY means that the client is assigned a whole
block of IPv6 addresses. This would be in line with the IPv6
addressing architecture in general, and with, e.g., the Framed-IPv6-
Prefix attribute is totally unnecessary.

Yet another possible in [RADIUS6]. However, the previous section

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rejected this interpretation for IPv4, so it would be seem strange to
adopt it only for IPv6.

Thus, if we assume that INTERNAL_IP4_NETMASK indicates and the prefix length in
INTERNAL_IP6_ADDRESS have the same meaning, and the reasoning in the
previous section is correct, then a broadcast address, meaning CFG_REPLY containing a prefix
length smaller than 128 has the same purpose as INTERNAL_IP6_SUBNET.

However, CFG_REQUESTs are more complicated. It seems that if a
client sends
CFG_REQUEST message that requests a packet to specific IPv6 address (usually an
address this address, the gateway will decrypt it
and send copies to all client was using earlier) should have prefix length 128.
But what do other VPN clients prefix lengths mean in CFG_REQUESTs?

Section 3.15.1 says that "With IPv6, a requestor MAY supply the low
order address range.
However, no implementation is known bytes it wants to do this, and use": presumably the prefix length
tells how many low order bits there is nothing
in are (i.e., if the IKEv2 spec that would support prefix length
is X, there requester supplies 128-X low order address bits).
However, this interpretation.

Fortunately, Section 4 clearly says that is quite confusing: if, say, a minimal implementation prefix length 126 means
that "I want to use these 128-126=2 low order bits", why does not need prefix
length 128 mean that "I want to include or understand use these 128 low order bits"?

Another interpretation is that instead of "low order", the INTERNAL_IP4_NETMASK
attribute, draft
should have said "high order", and thus a prefix length smaller than
128 means "I'd like to get an address from this subnet".

Given this very confusing discussion, this document recommends that
implementations should not use other INTERNAL_IP6_ADDRESS prefix
lengths than 128.

5.7 INTERNAL_IP6_NBNS

Section 3.15.1 defines the INTERNAL_IP4_NETMASK INTERNAL_IP6_NBNS attribute for sending
the IPv6 address of NetBIOS name servers.

However, NetBIOS is not defined for IPv6, and probably never will be.
Thus, this attribute most likely does not make much sense.

(Pointed out by Bernard Aboba in the IP Configuration Security (ICOS)
BoF at all.

(References: Charlie Kaufman's mail "RE: Proposed Last Call based
revisions to IKEv2", 2004-05-27. Email discussion with Tero Kivinen,
Jan 2005. Yoav Nir's mail "Re: New I-D: IKEv2 Clarifications IETF62.)

5.8 INTERNAL_ADDRESS_EXPIRY

Section 3.15.1 defines the INTERNAL_ADDRESS_EXPIRY attribute as
"Specifies the number of seconds that the host can use the internal
IP address. The host MUST renew the IP address before this expiry
time. Only one of these attributes MAY be present in the reply."

Expiry times and
Implementation Guidelines", 2005-02-07.) explicit renewals are primarily useful in

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5.5 Configuration payloads for IPv6

IKEv2 also defines configuration payloads for IPv6. However, they
are based on

environments like DHCP, where the corresponding IPv4 payloads, and do not fully follow server cannot reliably know when
the "normal IPv6 way of doing things".

A client has gone away. However, in IKEv2 this is known, and the
gateway can be assigned an IPv6 address using simply free the
INTERNAL_IP6_ADDRESS configuration payload. Presumably, address when the idea was IKE_SA is deleted.

Also, Section 4 says that a minimal exchange would look something like this:

CP(CFG_REQUEST) =
INTERNAL_IP6_ADDRESS()
INTERNAL_IP6_DNS()
TSi = (0, 0-65536, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65536, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)

In particular, IPv6 stateless autoconfiguration or router
advertisement messages are not used; neither supporting renewals is neighbor discovery.

While not mandatory.
Given that this approach functionality is reasonably simple, it has some limitations:
IPsec tunnels configured using IKEv2 are usually not fully-featured
"interfaces" in the IPv6 addressing architecture [IPv6Addr] sense.
In particular, they do needed, we recommend
that gateways should not necessarily have link-local addresses, and send the INTERNAL_ADDRESS_EXPIRY attribute.
(And since this may complicate attribute does not seem to make much sense for
CFG_REQUESTs, clients should not send it either.)

Note that according to Section 4, clients are required to understand
INTERNAL_ADDRESS_EXPIRY if the receive it. A minimum implementation
would use the value to limit the lifetime of protocols that assume them, such as
[MLDv2]. (Whether they are called "interfaces" in some particular
operating system is a different issue.) the IKE_SA.

(References: "VPN remote host configuration IPv6 ?" thread, May
2004.)

5.6 INTERNAL_IP6_ADDRESS prefix length

Earlier versions Tero Kivinen's mail "Comments of
draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05.
"Questions about internal address" thread, April 2005.)

6. Miscellaneous issues

6.1 Diffie-Hellman for first CHILD_SA

Section 1.2 shows that IKE_AUTH messages do not contain KEi/KEr or
Ni/Nr payloads. This implies that the IKEv2 draft had an INTERNAL_IP6_NETMASK
attribute corresponding to INTERNAL_IP4_NETMASK, but SA payload in IKE_AUTH
exchange cannot contain Transform Type 4 (Diffie-Hellman Group) with
any other value than NONE. Implementations should probably leave the
transform out entirely in this was deleted
when case.

6.2 Extended Sequence Numbers (ESN) transform

The description of the prefix length field was added ESN transform in Section 3.3 has be proved
difficult to understand. When the INTERNAL_IP6_ADDRESS
attribute. Thus, ESN transform is included, it seems logical to assume that their purpose would
be similar; however, has
the following meaning:

o A proposal containing one ESN transform with value 0 means "do not
use extended sequence numbers".

o A proposal containing one ESN transform with value 1 means "use
extended sequence numbers".

o A proposal containing two ESN transforms with values 0 and 1 means
"I support both normal and extended sequence numbers, you choose".
(Obviously this case is far from obvious.

The draft quite clearly says that only allowed in requests; the client is assigned an IPv6
address using response
will contain only one ESN transform.)

In most cases, the INTERNAL_IP6_ADDRESS attribute. However, as with exchange initiator will include either the netmask first
or third alternative in IPv4, it its SA payload. The second alternative is not clear what
rarely useful for the prefix length here
means. initiator: it means that using normal sequence

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Again, one possible interpretation

numbers is not acceptable (so if the responder does not support ESNs,
the exchange will fail with NO_PROPOSAL_CHOSEN).

Section 3.3.2 also says that a prefix length smaller
than 128 "If Transform Type 5 is not included in
a CFG_REPLY proposal, use of Extended Sequence Numbers is assumed". Or in
other words, omitting the ESN transform means that the client same thing as
including one ESN transform with value 1.

This choice of default value is assigned a whole
block somewhat counterintuitive and as
described above, rarely useful. IPsec WG decided recently to change
this part of IPv6 addresses. This would be in line with the IPv6
addressing architecture in general, specification, and with, e.g., the
Framed-IPv6-Prefix attribute in [RADIUS6]. However, the previous
section rejected this interpretation for IPv4, so make it would seem
strange mandatory to adopt it only include the
ESN transform for IPv6.

Thus, if we assume that INTERNAL_IP4_NETMASK and ESP/AH.

(References: "Technical change needed to IKEv2 before publication",
"STRAW POLL: Dealing with the prefix length ESN negotiation interop issue in
INTERNAL_IP6_ADDRESS have the same meaning, IKEv2"
and "Results of straw poll regarding: IKEv2 interoperability issue"
threads, March-April 2005.)

6.3 Matching ID_IPV4_ADDR and ID_IPV6_ADDR

When using the reasoning in the
previous section is correct, then a CFG_REPLY containing a prefix
length smaller than 128 has the same purpose as INTERNAL_IP6_SUBNET.

However, CFG_REQUESTs are more complicated. It seems that a
CFG_REQUEST message that requests a specific IPv6 address (usually an
address this client was using earlier) should have prefix length 128.
But what do other prefix lengths mean in CFG_REQUESTs?

Section 3.15.1 says that "With IPv6, a requestor MAY supply the low
order ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr
payloads, IKEv2 does not require this address bytes it wants to use": presumably the prefix length
tells how many low order bits there are (i.e., if match the prefix length
is X, there requester supplies 128-X low order address bits).
However, this in
the IP header (of IKEv2 packets), or anything in the TSi/TSr
payloads. The contents of IDi/IDr is quite confusing: if, say, a prefix length 126 means
that "I want used purely to use these 128-126=2 low order bits", why does prefix
length 128 mean that "I want fetch the policy
and authentication data related to use these 128 low order bits"?

Another interpretation is that instead of "low order", the draft
should have said "high order", other party.

(References: "Identities types IP address,FQDN/user FQDN and thus a prefix length smaller than
128 means "I'd like DN and
its usage in preshared key authentication" thread, Jan 2005.)

6.4 Relationship of IKEv2 to get an address from this subnet".

Given this very confusing discussion, this RFC2401bis

The IKEv2 document recommends that
implementations should not use other INTERNAL_IP6_ADDRESS prefix
lengths than 128.

5.7 INTERNAL_IP6_NBNS refers to [RFC2401bis], but it never makes clear
what the exact relationship is. That is probably because there is no
exact relationship. However, the IKEv2 document could state this
explicitly.

Section 3.15.1 defines 2.24 of IKEv2 says "Specifically, tunnel encapsulators and
decapsulators for all tunnel-mode Security Associations (SAs) created
by IKEv2 MUST support the INTERNAL_IP6_NBNS attribute ECN full-functionality option for sending tunnels
specified in [RFC3168] and MUST implement the IPv6 address tunnel encapsulation
and decapsulation processing specified in [RFC2401bis] to prevent
discarding of NetBIOS name servers.

However, NetBIOS is ECN congestion indications." This, in essence, says
that IKEv2 must be used with [RFC2401bis] only, not defined with RFC 2401,
because RFC 2401 has no requirements for IPv6, and probably never will be.
Thus, this attribute most likely does not make much sense.

(Pointed out by Bernard Aboba in ECN.

6.5 Reducing the IP Configuration Security (ICOS)
BoF at IETF62.)

6. Miscellaneous issues window size

In IKEv2, the window size is assumed to be a (possibly configurable)

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6.1 Diffie-Hellman for first CHILD_SA

Section 1.2 shows that IKE_AUTH messages do

property of a particular implementation, and is not contain KEi/KEr or
Ni/Nr payloads. This implies that related to
congestion control (unlike the SA payload window size in IKE_AUTH
exchange cannot contain Transform Type 4 (Diffie-Hellman Group) with
any other TCP, for instance).

In particular, it is not defined what the responder should do when it
receives a SET_WINDOW_SIZE notification containing a smaller value
than NONE.

6.2 Extended Sequence Numbers (ESN) transform

The description of the ESN transform is currently in Section 3.3 has be proved
difficult effect. Thus, there is currently no way to understand. When
reduce the ESN transform is included, it has window size of an existing IKE_SA. However, when rekeying
an IKE_SA, the following meaning:

o A proposal containing one ESN transform with value 0 means "do not
use extended sequence numbers".

o A proposal containing one ESN transform with value 1 means "use
extended sequence numbers".

o A proposal containing two ESN transforms new IKE_SA starts with values 0 and window size 1 means
"I support both normal and extended sequence numbers, you choose".
(Obviously this case is only allowed until it is
explicitly increased by sending a new SET_WINDOW_SIZE notification.

(References: Tero Kivinen's mail "Comments of
draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05.)

6.6 Minimum size of nonces

Section 2.10 says that "Nonces used in requests; IKEv2 MUST be randomly chosen,
MUST be at least 128 bits in size, and MUST be at least half the response
will contain only one ESN transform.)

In most cases, key
size of the negotiated prf."

However, the exchange initiator will include either chooses the first
or third alternative in its SA payload. The second alternative nonce before the outcome of the
negotiation is
rarely useful known. In this case, the nonce has to be long enough
for all the initiator: it means that using normal sequence
numbers PRFs being proposed.

6.7 Initial zero octets on port 4500

It is not acceptable (so if the responder does not support ESNs, clear whether a peer sending an IKE_SA_INIT request on port
4500 should include the exchange will fail with NO_PROPOSAL_CHOSEN). initial four zero octets. Section 3.3.2 also says that "If Transform Type 5 is 2.23 talks
about how to upgrade to tunneling over port 4500 after message 2, but
it does not included in
a proposal, use of Extended Sequence Numbers say what to do if message 1 is assumed". Or in
other words, omitting the ESN transform means the same thing sent on port 4500.

IKE MUST listen on port 4500 as
including one ESN transform with value 1.

This choice of default value is somewhat counterintuitive and well as
described above, rarely useful. There is ongoing discussion about
making including port 500.

[...]

The IKE initiator MUST check these payloads if present and if
they do not match the ESN transform mandatory, thus removing this
illogical default value.

(References: "Technical change needed to IKEv2 before publication" addresses in the outer packet MUST tunnel
all future IKE and "STRAW POLL: Dealing ESP packets associated with this IKE_SA over
UDP port 4500.

To tunnel IKE packets over UDP port 4500, the ESN negotiation interop issuein
IKEv2" threads, March 2005.)

6.3 Matching ID_IPV4_ADDR IKE header has four
octets of zero prepended and ID_IPV6_ADDR

When using the ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr
payloads, IKEv2 does not require this address to match result immediately follows the address
UDP header. [...]

The very beginning of Section 2 says "... though IKE messages may
also be received on UDP port 4500 with a slightly different format
(see section 2.23)."

That "slightly different format" is only described in discussing what

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to do after changing to port 4500. However, [RFC3948] shows clearly
the IP header (of IKEv2 packets), or anything in format has the TSi/TSr
payloads. The contents of IDi/IDr initial zeros even for initiators on port 4500.
Furthermore, without the initial zeros, the processing engine cannot
determine whether the packet is used purely to fetch an IKE packet or an ESP packet.

Thus, all packets sent on port 4500 need the policy
and authentication data related to four zero prefix;
otherwise, the other party.

(References: "Identities types IP address,FQDN/user FQDN and DN and
its usage in pershared key authentication" thread, Jan 2005.)

6.4 Relationship of IKEv2 to RFC2401bis

The IKEv2 document refers receiver won't know how to [RFC2401bis], but it never makes clear
what handle them.

6.8 SPI values in IKE_SA_INIT exchange

Normal IKE messages include the exact relationship is. That is probably because there is no
exact relationship. initiator's and responder's SPIs,
both of which are non-zero, in the IKE header. However, there are
some corner cases where the IKEv2 document could state this
explicitly.

IKEv2 can specification is not fully
consistent about what values should be used with either [RFC2401] or [RFC2401bis], except in
places used.

First, Section 3.1 says that are only covered by [RFC2401bis]. The areas specific to
[RFC2401bis] are ECN (Section 2.24), fragmentation control (Section
3.10), and the use of opaque ports Responder's SPI "...MUST NOT be zero
in traffic selectors (Section
3.13.1). IKEv2 allows any other message" (than the creation first message of a single SA that has multiple
protocols when being used with [RFC2401]; this is not allowed in
[RFC2401bis].

6.5 Reducing the window size

In IKEv2, IKE_SA_INIT
exchange). However, the window size is assumed to be a (possibly configurable)
property of a particular implementation, and is not related to
congestion control (unlike figure in Section 2.6 shows the window size second
IKE_SA_INIT message as "HDR(A,0), N(COOKIE)", contradicting the text
in TCP, for instance).

In particular, there is no way to reduce 3.1.

Since the window size of an
existing IKE_SA. However, when rekeying an IKE_SA, responder's SPI identifies security-related state held by
the new IKE_SA
starts with window size 1 until it responder, and in this case no state is explicitly increased by created, sending a new SET_WINDOW_SIZE notification.

6.6 Minimum size of nonces

Section 2.10 says that "Nonces used zero
value seems reasonable.

Second, in IKEv2 MUST be randomly chosen,
MUST be at least 128 bits addition to cookies, there are several other cases when
the IKE_SA_INIT exchange does not result in size, and MUST be at least half the key
size creation of an IKE_SA
(for instance, INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN). What
responder SPI value should be used in the negotiated prf."

However, the initiator chooses IKE_SA_INIT response in
this case?

Since the nonce before IKE_SA_INIT request always has a zero responder SPI, the outcome of
value will not be actually used by the
negotiation initiator. Thus, we think
sending a zero value is known. In correct also in this case, case.

There is also an important detail about the nonce has to Initiator SPI that must
be long enough
for all taken into account by responders. If a responder receives two
IKE_SA_INIT requests with the PRFs being proposed.

6.7 Initial zero octets on port 4500 same Initiator SPI, it must not
automatically conclude that the latter is a retransmission of the
former. It is possible that the packets were sent by two different
peers that just happened to choose the same Initiator SPI (IKEv2 does
not clear whether a peer sending an IKE_SA_INIT request on port
4500 require that SPIs are chosen randomly). Instead, the responder
should include compare the initial four zero octets. Section 2.23 talks
about how whole packets (or at the minimum, Ni payloads,
which are always chosen randomly) to upgrade determine whether or not this
packet creates a new IKE_SA or belongs to tunneling over port 4500 after message 2, but an existing IKE_SA.

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it does not say what to do if message 1 is sent on port 4500.

IKE MUST listen on port 4500 as well as port 500.

[...]

6.9 SPI values for messages outside of an IKE_SA

The IKE initiator MUST check these payloads if present and if
they do IKEv2 specification does not match the addresses say what SPI values should be used
in the outer packet MUST tunnel
all future IKE and ESP packets associated with this IKE_SA over
UDP port 4500.

To tunnel IKE packets over UDP port 4500, the IKE header has four
octets of zero prepended and the result immediately follows for the
UDP header. [...]

The very beginning small number of notifications that are
allowed to be sent outside of an IKE_SA. Note that such
notifications are explicitly *not* Informational exchanges; Section 2 says "... though IKE
1.5 makes it clear that these are one-way messages may
also that must not be received on UDP port 4500 with
responded to.

There are two cases when such a slightly different format
(see section 2.23)."

That "slightly different format" is only described in discussing what
to do after changing one-way notification can be sent:
INVALID_IKE_SPI and INVALID_SPI. In both cases, there are no IKE SPI
values that would be meaningful to port 4500. However, [RFC3948] shows clearly the format has recipient of such a
notification.

A strict interpretation of the initial zeros even for initiators on port 4500.
Furthermore, without specification would require the initial zeros, sender
to invent garbage values for the processing engine cannot
determine whether SPI fields. However, we think this
was not the packet intention, and using zero values is acceptable.

6.10 Protocol ID/SPI fields in Notify payloads

Section 3.10 says that the Protocol ID field in Notify payloads "For
notifications which do not relate to an IKE packet or an ESP packet.

Thus, all packets existing SA, this field MUST
be sent on port 4500 need the four as zero prefix;
otherwise, and MUST be ignored on receipt". However, the receiver won't know how
specification does not clearly say which notifications are related to handle them.

6.8 SPI values in IKE_SA_INIT exchange

Normal IKE messages include the initiator's
existing SAs and responder's SPIs,
both of which are non-zero, in not.

Since the IKE header. However, there are
some corner cases where main purpose of the IKEv2 specification Protocol ID field is not fully
consistent about what values to specify the
type of the SPI, our interpretation is that the Protocol ID field
should be used.

First, non-zero only when the SPI field is non-empty.

There are currently only two notifications where this is the case:
INVALID_SELECTORS and REKEY_SA.

6.11 INVALID_IKE_SPI

Section 3.1 3.10.1 says that the Responder's INVALID_IKE_SPI notification "indicates
an IKE message was received with an unrecognized destination SPI.
This usually indicates that the recipient has rebooted and forgotten
the existence of an IKE_SA."

The text does not say whether the SPI "...MUST NOT value should be zero included in any other message" (than the first message of the IKE_SA_INIT
exchange).
notification. However, it is clear that the figure in Section 2.6 shows notification will be
useful to the second
IKE_SA_INIT message as "HDR(A,0), N(COOKIE)", contradicting recipient only if it can find the text
in 3.1.

Since IKE_SA somehow, so
the responder's SPI identifies security-related state held by
the responder, should be included.

This still leaves two questions open: which SPI(s) should be
included, and in this case no state is created, sending a zero
value seems reasonable.

Second, in addition to cookies, there how it (or they) should be sent. For the first
question, the alternatives are several other cases when the IKE_SA_INIT exchange does not result in unrecognized destination SPI, the creation of an IKE_SA
(for instance, INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN). What

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responder

source SPI value should (which presumably would be used in more useful for the IKE_SA_INIT response in
this case?

Since recipient),
or both. For the IKE_SA_INIT request always has a zero responder SPI, second question, the
value will not SPI(s) could be actually used by the initiator. Thus, we think
sending a zero value is correct also placed in this case.

6.9 SPI values for messages outside of an IKE_SA

The IKEv2 specification does not say what the
SPI values should be used
for Informational requests sent outside of an IKE_SA.

There seem to be two cases when such a message can be sent:
INVALID_IKE_SPI and INVALID_SPI notifications. Especially field(s) in the
latter case, no meaningful IKE header, the SPI values are available.

A strict interpretation of field in the specification would require Notify payload,
or the sender
to invent garbage values for Notification Data field.

In the SPI fields. However, we think this
was not case of another related notification, INVALID_SPI, the intention, and using zero values
situation is acceptable.

6.10 Protocol ID/SPI fields in Notify payloads

Section 3.10 clearer: there is only a single SPI, and the text
explicitly says that the Protocol ID field in Notify payloads "For
notifications which do SPI is sent as Notification Data (since the
notification is not relate to about an existing SA, this the SPI field MUST
be sent as zero and MUST be ignored on receipt". However, in the
specification does Notify
payload is not clearly say which notifications are related to
existing SAs used; and which are not. obviously the value cannot be placed in the
IKE header).

Since the main purpose of the Protocol ID field INVALID_IKE_SPI notification is to specify the
type sent outside of the SPI, our interpretation an IKE_SA,
and it is not about an existing SA, it seems that the Protocol ID field
should using Notification
Data would be non-zero only when the SPI field is non-empty.

There are currently only two notifications where logical choice. However, this is the case:
INVALID_SELECTORS issue needs more
discussion and REKEY_SA.

6.11 INVALID_IKE_SPI we do not yet propose any solution in this document.

6.12 Which message should contain INITIAL_CONTACT

The description of the INITIAL_CONTACT notification in Section 3.10.1
says that the INVALID_IKE_SPI "This notification "indicates
an IKE message was received with an unrecognized destination SPI.
This usually indicates asserts that this IKE_SA is the recipient has rebooted and forgotten only
IKE_SA currently active between the existence of an IKE_SA." authenticated identities".
However, neither Section 2.4 nor 3.10.1 says in which message this
payload should be placed.

The text does not say whether talk about authenticated identities, so it seems the SPI value should
notification cannot be included in sent before both endpoints have been
authenticated. Thus, the
notification. However, possible places are the last IKE_AUTH
response message and a separate Informational exchange.

Based on how this was implemented in IKEv1, it is clear that seems the notification will be
useful intent was
to use a separate Informational exchange.

(References: "Clarifying the recipient only if it can find use of INITIAL_CONTACT in IKEv2" thread,
April 2005. "Initial Contact messages" thread, December 2004.
"IKEv2 and Initial Contact" thread, September 2004.)

6.13 Message IDs for IKE_SA_INIT messages

The Message ID for IKE_SA_INIT messages is always zero. This
includes retries of the message due to responses such as COOKIE and
INVALID_KE_PAYLOAD.

This is because Message IDs are part of the IKE_SA somehow, so state, and when
the SPI should be included.

This still leaves two questions open: which SPI(s) should be responder replies to IKE_SA_INIT request with N(COOKIE) or
N(INVALID_KE_PAYLOAD), the responder does not allocate any state.

(References: "Question about N(COOKIE) and N(INVALID_KE_PAYLOAD)

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included, and how it (or they) should

combination" thread, Oct 2004. Tero Kivinen's mail "Comments of
draft-eronen-ipsec-ikev2-clarifications-02.txt", 2005-04-05.)

6.14 Message IDs for IKE_AUTH messages

According to Section 2.2, "The IKE_SA initial setup messages will
always be sent. For numbered 0 and 1." That is true when the IKE_AUTH exchange
does not use EAP. When EAP is used, each pair of messages have their
message numbers incremented. The first
question, pair of AUTH messages will
have an ID of 1, the alternatives are second will be 2, and so on.

(References: "Question about MsgID in AUTH exchange" thread, April
2005.)

6.15 Creating an IKE_SA without a CHILD_SA

It is recommended that the unrecognized destination SPI, responder set up an IKE_SA even if it is
not possible to set up a CHILD_SA, as long as there is agreement on
the
source SPI (which presumably would be more useful for cryptographic parts of the recipient),
or both. For IKE_SA. This might happen when the second question,
parties in the SPI(s) could be placed IKE_AUTH exchange agree on cryptographic protocols but
fail to agree on IPsec issues. The list of responses in the IKE_AUTH
exchange that should not prevent an IKE_SA from being set up include
NO_PROPOSAL_CHOSEN, SINGLE_PAIR_REQUIRED, INTERNAL_ADDRESS_FAILURE,
FAILED_CP_REQUIRED, and TS_UNACCEPTABLE.

(References: "Questions about internal address" thread, April, 2005.)

6.16 Alignment of payloads

Many IKEv2 payloads contain fields marked as "RESERVED", mostly
because IKEv1 had them, and partly because they make the pictures
easier to draw. In particular, payloads in IKEv2 are not, in
general, aligned to 4-byte boundaries. (Note that payloads were not
aligned to 4-byte boundaries in the
SPI field(s) IKEv1 either.)

(References: "IKEv2: potential 4-byte alignment problem" thread, June
2004.)

6.17 Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED

The description of ESP_TFC_PADDING_NOT_SUPPORTED notification in
Section 3.10.1 says that "This notification asserts that the IKE header, sending
endpoint will NOT accept packets that contain Flow Confidentiality
(TFC) padding".

However, the SPI field text does not say in the Notify payload, which messages this notification
should be included, or whether the Notification Data field.

In the case scope of another related notification, INVALID_SPI, the
situation is clearer: there this notification is only a
single SPI, and CHILD_SA or all CHILD_SAs of the text
explicitly says peer.

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Our interpretation is that the SPI scope is sent as Notification Data (since the a single CHILD_SA, and thus
this notification is not about an existing SA, the SPI field included in the Notify messages containing an SA payload is not used; and obviously the value cannot
negotiating a CHILD_SA. If neither endpoint accepts TFC padding,
this notification will be placed included in both the
IKE header).

Since the INVALID_IKE_SPI notification is sent outside of request proposing an IKE_SA,
SA and it is not about an existing SA, it seems that using Notification
Data would be the logical choice. However, response accepting it. If this issue needs more
discussion and we do not yet propose any solution notification is included
in this document.

6.12 Which message should contain INITIAL_CONTACT

The description only one of the INITIAL_CONTACT messages, TFC padding can still be sent in one
direction.

6.18 Negotiation of NON_FIRST_FRAGMENTS_ALSO

NON_FIRST_FRAGMENTS_ALSO notification is described in Section 3.10.1
simply as "Used for fragmentation control. See [RFC2401bis] for
explanation."

[RFC2401bis] says "Implementations that "This notification asserts will transmit non-initial
fragments on a tunnel mode SA that this IKE_SA is the only
IKE_SA currently active between makes use of non-trivial port (or
ICMP type/code or MH type) selectors MUST notify a peer via the authenticated identities".
However, neither Section 2.4 nor 3.10.1 says IKE
NOTIFY NON_FIRST_FRAGMENTS_ALSO payload. The peer MUST reject this
proposal if it will not accept non-initial fragments in which message this
payload should be placed.

The text context.
If an implementation does talk about authenticated identities, so not successfully negotiate transmission of
non-initial fragments for such an SA, it seems MUST NOT send such fragments
over the SA."

However, it is not clear exactly how the negotiation works. Our
interpretation is that the negotiation works the same way as for
IPCOMP_SUPPORTED and USE_TRANSPORT_MODE: sending non-first fragments
is enabled only if NON_FIRST_FRAGMENTS_ALSO notification cannot be sent before is included
in both endpoints have been
authenticated. Thus, the possible places are request proposing an SA and the last IKE_AUTH response message and a separate Informational exchange.

Based on how accepting it.
In other words, if the peer "rejects this was implemented in IKEv1, proposal", it seems only omits
NON_FIRST_FRAGMENTS_ALSO notification from the intent was
to use a separate Informational exchange. response, but does not
reject the whole CHILD_SA creation.

7. Status of the clarifications

This document is work-in-progress, and it contains both relatively
stable and finished parts, and other parts that are incomplete or
even incorrect. To help the reader in deciding how much weight
should be given to each clarification, this section contains our
opinions about which parts we believe to are stable, and which are
likely to change in future versions.

Those clarifications believed to be correct and without controversy
are marked with three asterisks (***); those where the clarification
is known to be incomplete and/or there is disagreement about what the
correct interpretation is are marked with one asterisk (*). The

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clarifications marked with two asterisks (**) are somewhere between
the extremes.

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2. Authentication
2.1 Data included in AUTH payload calculation ***
2.2 Hash function for RSA signatures ***
2.3 Encoding method for RSA signatures ***
2.4 Identification type for EAP ***
2.5 Identity for policy lookups when using EAP ***
2.6 EAP authentication and the AUTH payload ***
2.7 Certificate encoding types ***
2.8 Shared key authentication and fixed PRF key size **
2.9 EAP authentication and fixed PRF key size *
2.10 Matching ID payloads to certificate contents ***
3. Keying and rekeying
3.1 Semantics of the CREATE_CHILD_SA exchange *
3.2 Rekeying the IKE_SA vs. reauthentication **
3.3 SPIs when rekeying the IKE_SA ***
3.4 Which SPI to use in REKEY_SA ***
3.5 Changing PRFs when rekeying the IKE_SA *
3.6 Deleting vs. closing SAs **
3.7 Deleting an SA pair **
3.8 Deleting an IKE_SA **
3.9 Who is the original initiator of IKE_SA **
4. Traffic selectors
4.1 Semantics of complex traffic selector payloads ***
4.2 ICMP type/code in traffic selector payloads ***
4.3 Mobility header in traffic selector payloads ***
4.4 Narrowing the traffic selectors ***
4.5 SINGLE_PAIR_REQUIRED **
4.6 Traffic selectors violating own policy *
5. Configuration payloads
5.1 Length of configuration attribute type field ***
5.2 Requesting any INTERNAL_IP4/IP6_ADDRESS ***
5.3 INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET **
5.4 INTERNAL_IP4_NETMASK **
5.5 Configuration payloads for IPv6 *
5.6 INTERNAL_IP6_ADDRESS prefix length *
5.7 INTERNAL_IP6_NBNS ***
5.8 INTERNAL_ADDRESS_EXPIRY **
6. Miscellaneous issues
6.1 Diffie-Hellman for first CHILD_SA ***
6.2 Extended Sequence Numbers (ESN) transform **
6.3 Matching ID_IPV4_ADDR and ID_IPV6_ADDR ***
6.4 Relationship of IKEv2 to RFC2401bis **
6.5 Reducing the window size **
6.6 Minimum size of nonces ***
6.7 Initial zero octets on port 4500 ***
6.8 SPI values in IKE_SA_INIT exchange **
6.9 SPI values for messages outside of an IKE_SA *
6.10 Protocol ID/SPI fields in Notify an IKE_SA *
6.10 Protocol ID/SPI fields in Notify payloads **

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6.11 INVALID_IKE_SPI *
6.12 Which message should contain INITIAL_CONTACT **
6.13 Message IDs for IKE_SA_INIT messages **
6.14 Message IDs for IKE_AUTH messages ***
6.15 Creating an IKE_SA without a CHILD_SA **
6.16 Alignment of payloads ***
6.17 Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED **
6.11 INVALID_IKE_SPI *
6.12 Which message should contain INITIAL_CONTACT
6.18 Negotiation of NON_FIRST_FRAGMENTS_ALSO **

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Future versions of this document will, of course, change these
estimates (and changes in both directions are possible, though
hopefully it's more towards higher confidence).

8. Implementation mistakes

Some implementers at the first IKEv2 bakeoff didn't do everything
correctly. This may seem like an obvious statement, but it is
probably useful to list a few things that were clear in the document
and not needing clarification, that some implementors didn't do. All
of these things caused interoperability problems.

o Some implementations continued to send traffic on a CHILD_SA after
it was rekeyed, even after receiving an DELETE payload.

o After rekeying an IKE_SA, some implementations did not reset their
message counters to zero. One set the counter to 2, another did
not reset the counter at all.

o Some implementations could only handle a single pair of traffic
selectors, or would only process the first pair in the proposal.

9. Open issues

This section lists issues that this document probably should address,
but has not done so yet.

o In the traffic selector discussion, we need to come up with better
wording for the "sender's inbound" SAs. Is that traffic that is
being sent to the sender, or traffic being sent from the sender?

o Many of the configuration payload issues in this draft are still
far from clear. These need to be resolved before implementers can
feel assured of creating interoperable implementations.

o There may need Some implementations responded to be more text about deleting an old SA after
rekeying is finished.

o The text about sending a DELETE for only one direction of an SA
(and the responder delete request by sending the DELETE for the other direction of
the SA in its response) doesn't explain the logic, an
empty INFORMATIONAL response, and doesn't say
why you should not send DELETEs for both directions of then initiated their own
INFORMATIONAL exchange with the SA. We
need to add a description pair of the race condition if one side
deletes both SAs at once. to delete.

o When Although this did not happen at the document uses bakeoff, from the term "original initiator" (or similar
terms), discussion
there, it is not clear whether or that some people had not implemented message
window sizes correctly. Some implementations might have sent
messages that did not fit into the responder's message windows,
and some implementations may not have torn down an SA if they did
not ever receive a message that they know they should have.

9. Open issues

This section lists issues that term also applies to this document probably should address,
but has not done so yet.

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the side that originates an rekeying

o Many of the IKE_SA. That is, if
Alice starts the first IKE_SA, but then Bob rekeys the IKE_SA, is
the "original initiator" from that point on now Bob, or is it configuration payload issues in this draft are still Alice? Also, if it is Bob, at what exact point does it
become Bob? This needs
far from clear. These need to be cleared up on a case-by-case basis
throughout the document. resolved before implementers can
feel assured of creating interoperable implementations.

o It would be very useful to have actual examples of certificate
type 12 (hash and URL of X.509 certificates) and type 13 (hash and
URL of X.509 bundle).

o The message IDs of IKE_SA_INIT messages is unclear if there are
cookies followed by INVALID_KE_PAYLOAD. See "Question about
N(COOKIE) and N(INVALID_KE_PAYLOAD) combination" thread, Oct 2004. This definitely needs to be clarified.

o There is some confusion on when document might want to emit and process
INITIAL_CONTACT payloads. References: Michael Richardson's mail
"Initial Contact Messages", 2004-12-05. Paul Hoffman's reply,
2004-12-05. Tero Kivinen's reply, 2004-12-07. "Replicated
identities" thread in Jan 2005.) It is explicitly talk about not clear if there doing ESP-
in-AH even though it is an
interoperability issue because reacting possible. We could say "implementations
do not need to INITIAL_CONTACT is
optional, but this should be cleared up. support this".

10. Security considerations

This document does not introduce any new security considerations to
IKEv2. If anything, clarifying complex areas of the specification
can reduce the likelihood of implementation problems that may have
security implications.

11. IANA considerations

This document does not change or create any IANA-registered values.

12. Acknowledgments

This document is mainly based on conversations on the IPsec WG
mailing list. The authors would especially like to thank Bernard
Aboba, Jari Arkko, Vijay Devarapalli, William Dixon, Mika
Joutsenvirta, Charlie Kaufman, Tero Kivinen, Yoav Nir, and Michael
Richardson for their contributions.

In addition, the authors would like to thank all the participants of
the first public IKEv2 bakeoff, held in Santa Clara in February 2005,
for their questions and proposed clarifications.

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13. References

13.1 Normative References

[IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", draft-ietf-ipsec-ikev2-17 (work in progress),
September 2004.

[IKEv2ALG]
Schiller, J., "Cryptographic Algorithms for use in the
Internet Key Exchange Version 2",
draft-ietf-ipsec-ikev2-algorithms-05 (work in progress),

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April 2004.

[PKCS1v20]
Kaliski, B. and J. Staddon, "PKCS #1: RSA Cryptography
Specifications Version 2.0", RFC 2437, October 1998.

[PKCS1v21]
Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.

[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.

[RFC2401bis]
Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", draft-ietf-ipsec-rfc2401bis-05 draft-ietf-ipsec-rfc2401bis-06 (work
in progress), December 2004. March 2005.

13.2 Informative References

[EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.

[EAPKey] Aboba, B., Simon, D., Arkko, J., Eronen, P. P., and H.
Levkowetz, "Extensible Authentication Protocol (EAP) Key
Management Framework", draft-ietf-eap-keying-04 draft-ietf-eap-keying-06 (work in
progress), November 2004. April 2005.

[IPCPSubnet]
Cisco Systems, Inc., "IPCP Subnet Mask Support
Enhancements",
http://www.cisco.com/univercd/cc/td/doc/product/software/i
os121/121newft/121limit/121dc/121dc3/ipcp_msk.htm, http://www.cisco.com/univercd/cc/td/doc/
product/software/ios121/121newft/121limit/121dc/121dc3/
ipcp_msk.htm, January 2003.

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[IPv6Addr]
Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2004.

[MIPv6] Johnson, D., Perkins, C. C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.

[MLDv2] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

[NAI] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.

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[NAIbis] Aboba, B., Beadles, M., Arkko, J. J., and P. Eronen, "The
Network Access Identifier",
draft-ietf-radext-rfc2486bis-03
draft-ietf-radext-rfc2486bis-05 (work in progress),
November 2004.
February 2005.

[RADEAP] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.

[RADIUS] Rigney, C., Willens, S., Rubens, A. A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.

[RADIUS6] Aboba, B., Zorn, G. G., and D. Mitton, "RADIUS and IPv6",
RFC 3162, August 2001.

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

[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.

[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L. L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.

[RFC822] Crocker, D., "Standard for the format of ARPA Internet
text messages", RFC 822, August 1982.

[ReAuth] Nir, Y., "Repeated Authentication in IKEv2",
draft-nir-ikev2-auth-lt-01
draft-nir-ikev2-auth-lt-02 (work in progress), November
2004. May 2005.

[SCVP] Freeman, T., Housley, R. and A. T., Housley, R., Malpani, A., Cooper, D., and T.
Polk, "Simple Certificate Validation Protocol (SCVP)",

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draft-ietf-pkix-scvp-16
draft-ietf-pkix-scvp-18 (work in progress), October 2004. February 2005.

Authors' Addresses

Pasi Eronen
Nokia Research Center
P.O. Box 407
FIN-00045 Nokia Group
Finland

EMail:

Email: pasi.eronen@nokia.com

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Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
USA

EMail:

Email: paul.hoffman@vpnc.org

Appendix A. Exchanges and payloads

This appendix contains a short summary of the IKEv2 exchanges, and
what payloads can appear in which message. This appendix is purely
informative; if it disagrees with the body of this document or the
IKEv2 specification, the other text is considered correct.

Vendor-ID (V) payloads may be included in any place in any message.
This sequence shows what are, in our opinion, the most logical places
for them.

The specification does not say which messages can contain
N(SET_WINDOW_SIZE). It can possibly be included in any message, but
it is not yet shown below.

Note: N(INITIAL_CONTACT) is still under discussion and is not shown
below.

A.1 IKE_SA_INIT exchange

request --> [N(COOKIE)],
SA, KE, Ni,
[N(NAT_DETECTION_SOURCE_IP)+,
N(NAT_DETECTION_DESTINATION_IP)],
[V+]

normal response <-- SA, KE, Nr,
(no cookie) [N(NAT_DETECTION_SOURCE_IP),
N(NAT_DETECTION_DESTINATION_IP)],
[[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
[V+]

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A.2 IKE_AUTH exchange without EAP

request --> IDi, [CERT+],
[[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
[IDr],
AUTH,
[CP(CFG_REQUEST)],
[N(IPCOMP_SUPPORTED)+],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[V+]

response <-- IDr, [CERT+],
AUTH,
[CP(CFG_REPLY)],
[N(IPCOMP_SUPPORTED)],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[N(ADDITIONAL_TS_POSSIBLE)],
[V+]

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A.3 IKE_AUTH exchange with EAP

first request --> IDi,
[[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
[IDr],
[CP(CFG_REQUEST)],
[N(IPCOMP_SUPPORTED)+],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[V+]

first response <-- IDr, [CERT+], AUTH,
EAP,
[V+]

/ --> EAP
repeat 1..N times |
\ <-- EAP

last request --> AUTH

last response <-- AUTH,
[CP(CFG_REPLY)],
[N(IPCOMP_SUPPORTED)],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, TSi, TSr,
[N(ADDITIONAL_TS_POSSIBLE)],
[V+]

A.4 CREATE_CHILD_SA exchange for creating/rekeying CHILD_SAs

request --> [N(REKEY)],
[N(IPCOMP_SUPPORTED)+],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, Ni, [KEi], TSi, TSr

response <-- [N(IPCOMP_SUPPORTED)],
[N(USE_TRANSPORT_MODE)],
[N(ESP_TFC_PADDING_NOT_SUPPORTED)],
[N(NON_FIRST_FRAGMENTS_ALSO)],
SA, Nr, [KEr], TSi, TSr,
[N(ADDITIONAL_TS_POSSIBLE)]

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A.5 CREATE_CHILD_SA exchange for rekeying the IKE_SA

request --> N(REKEY),
SA, Ni, [KEi]

response <-- SA, Nr, [KEr]

A.6 INFORMATIONAL exchange

request --> [N+],
[D+],
[CP(CFG_REQUEST)]

response <-- [N+],
[D+],
[CP(CFG_REPLY)]

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