[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 02 03 04 05 06 07 08 09 RFC 4718

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


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

Status of this Memo

   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 becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 3, 2005.

Copyright Notice

   Copyright (C) The Internet Society (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.





Eronen & Hoffman        Expires December 3, 2005                [Page 1]

Internet-Draft            IKEv2 Clarifications                 June 2005


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  . . . . . . . . . . . . . .  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 . . . . . . . . . . . . . . . . .  15
     3.8  Deleting an IKE_SA . . . . . . . . . . . . . . . . . . . .  15
     3.9  Who is the original initiator of IKE_SA  . . . . . . . . .  15
   4.   Traffic selectors  . . . . . . . . . . . . . . . . . . . . .  16
     4.1  Semantics of complex traffic selector payloads . . . . . .  16
     4.2  ICMP type/code in traffic selector payloads  . . . . . . .  16
     4.3  Mobility header in traffic selector payloads . . . . . . .  17
     4.4  Narrowing the traffic selectors  . . . . . . . . . . . . .  17
     4.5  SINGLE_PAIR_REQUIRED . . . . . . . . . . . . . . . . . . .  17
     4.6  Traffic selectors violating own policy . . . . . . . . . .  18
   5.   Configuration payloads . . . . . . . . . . . . . . . . . . .  19
     5.1  Length of configuration attribute type field . . . . . . .  19
     5.2  Requesting any INTERNAL_IP4/IP6_ADDRESS  . . . . . . . . .  19
     5.3  INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET  . . . . . . . . .  19
     5.4  INTERNAL_IP4_NETMASK . . . . . . . . . . . . . . . . . . .  22
     5.5  Configuration payloads for IPv6  . . . . . . . . . . . . .  23
     5.6  INTERNAL_IP6_ADDRESS prefix length . . . . . . . . . . . .  24
     5.7  INTERNAL_IP6_NBNS  . . . . . . . . . . . . . . . . . . . .  25
     5.8  INTERNAL_ADDRESS_EXPIRY  . . . . . . . . . . . . . . . . .  25
   6.   Miscellaneous issues . . . . . . . . . . . . . . . . . . . .  26
     6.1  Diffie-Hellman for first CHILD_SA  . . . . . . . . . . . .  26
     6.2  Extended Sequence Numbers (ESN) transform  . . . . . . . .  26
     6.3  Matching ID_IPV4_ADDR and ID_IPV6_ADDR . . . . . . . . . .  27
     6.4  Relationship of IKEv2 to RFC2401bis  . . . . . . . . . . .  27
     6.5  Reducing the window size . . . . . . . . . . . . . . . . .  27
     6.6  Minimum size of nonces . . . . . . . . . . . . . . . . . .  28
     6.7  Initial zero octets on port 4500 . . . . . . . . . . . . .  28



Eronen & Hoffman        Expires December 3, 2005                [Page 2]

Internet-Draft            IKEv2 Clarifications                 June 2005


     6.8  SPI values in IKE_SA_INIT exchange . . . . . . . . . . . .  29
     6.9  SPI values for messages outside of an IKE_SA . . . . . . .  30
     6.10   Protocol ID/SPI fields in Notify payloads  . . . . . . .  30
     6.11   INVALID_IKE_SPI  . . . . . . . . . . . . . . . . . . . .  30
     6.12   Which message should contain INITIAL_CONTACT . . . . . .  31
     6.13   Message IDs for IKE_SA_INIT messages . . . . . . . . . .  31
     6.14   Message IDs for IKE_AUTH messages  . . . . . . . . . . .  32
     6.15   Creating an IKE_SA without a CHILD_SA  . . . . . . . . .  32
     6.16   Alignment of payloads  . . . . . . . . . . . . . . . . .  32
     6.17   Negotiation of ESP_TFC_PADDING_NOT_SUPPORTED . . . . . .  32
     6.18   Negotiation of NON_FIRST_FRAGMENTS_ALSO  . . . . . . . .  33
   7.   Status of the clarifications . . . . . . . . . . . . . . . .  33
   8.   Implementation mistakes  . . . . . . . . . . . . . . . . . .  35
   9.   Open issues  . . . . . . . . . . . . . . . . . . . . . . . .  35
   10.  Security considerations  . . . . . . . . . . . . . . . . . .  36
   11.  IANA considerations  . . . . . . . . . . . . . . . . . . . .  36
   12.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  36
   13.  References . . . . . . . . . . . . . . . . . . . . . . . . .  36
     13.1   Normative References . . . . . . . . . . . . . . . . . .  36
     13.2   Informative References . . . . . . . . . . . . . . . . .  37
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  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 . . . . . . .  43






















Eronen & Hoffman        Expires December 3, 2005                [Page 3]

Internet-Draft            IKEv2 Clarifications                 June 2005


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:








Eronen & Hoffman        Expires December 3, 2005                [Page 4]

Internet-Draft            IKEv2 Clarifications                 June 2005


       InitiatorSignedOctets = RealMessage1 | NonceRData | MACedIDForI
       GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR
       RealIKEHDR =  SPIi | SPIr |  . . . | Length
       RealMessage1 = RealIKEHDR | RestOfMessage1
       NonceRPayload = PayloadHeader | NonceRData
       InitiatorIDPayload = PayloadHeader | RestOfIDPayload
       RestOfInitIDPayload = IDType | RESERVED | InitIDData
       MACedIDForI = prf(SK_pi, RestOfInitIDPayload)

   The responder's signed octets can be described as:

       ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR
       GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR
       RealIKEHDR =  SPIi | SPIr |  . . . | Length
       RealMessage2 = RealIKEHDR | RestOfMessage2
       NonceIPayload = PayloadHeader | NonceIData
       ResponderIDPayload = PayloadHeader | RestOfIDPayload
       RestOfRespIDPayload = IDType | RESERVED | InitIDData
       MACedIDForR = prf(SK_pr, RestOfRespIDPayload)


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



Eronen & Hoffman        Expires December 3, 2005                [Page 5]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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), 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.



Eronen & Hoffman        Expires December 3, 2005                [Page 6]

Internet-Draft            IKEv2 Clarifications                 June 2005


   (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.










Eronen & Hoffman        Expires December 3, 2005                [Page 7]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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,



Eronen & Hoffman        Expires December 3, 2005                [Page 8]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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.)

2.10  Matching ID payloads to 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".



Eronen & Hoffman        Expires December 3, 2005                [Page 9]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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.

   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



Eronen & Hoffman        Expires December 3, 2005               [Page 10]

Internet-Draft            IKEv2 Clarifications                 June 2005


        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
        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



Eronen & Hoffman        Expires December 3, 2005               [Page 11]

Internet-Draft            IKEv2 Clarifications                 June 2005


        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:

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

        The initiator sends SA offer(s) in the SA payload, a nonce in
        the Ni payload, and 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}

        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 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}             -->

        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. When rekeying an existing
        CHILD_SA, the leading N payload of type REKEY_SA MUST be



Eronen & Hoffman        Expires December 3, 2005               [Page 12]

Internet-Draft            IKEv2 Clarifications                 June 2005


        included and MUST give the SPI (as they would be expected in
        the headers of inbound 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.

        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.


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].



Eronen & Hoffman        Expires December 3, 2005               [Page 13]

Internet-Draft            IKEv2 Clarifications                 June 2005


   (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.)

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



Eronen & Hoffman        Expires December 3, 2005               [Page 14]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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.

3.7  Deleting a CHILD_SA pair

   Section 1.4 describes how to delete SA pairs using the Informational
   exchange: "To delete an SA, an INFORMATIONAL Exchange with one or
   more delete payloads is sent listing the SPIs (as they would be
   expected in the headers of inbound packets) of the SAs to be deleted.
   The recipient MUST close the designated SAs."

   The "one or more delete payloads" phrase has caused some confusion.
   You never send delete payloads for the two sides of an SA in a single
   message.  If you have many SAs to delete at the same time (such as
   the nested example given in that paragraph), you include delete
   payloads for in inbound half or each SA in your Informational
   exchange.

3.8  Deleting an IKE_SA

   Since IKE_SAs do not exist in pairs, it is not totally clear what the
   response message should contain when the request deleted the IKE_SA.

   Since there is no information that needs to be sent to the other side
   (except that the request was received), an empty Informational
   response seems like the most logical choice.

   (References: "Question about delete IKE SA" thread, May 2005.)

3.9  Who is the original initiator of IKE_SA

   In the IKEv2 document, "initiator" refers to the party who initiated
   the exchange being described, and "original initiator" refers to the
   party who initiated the whole IKE_SA.  However, there is some
   potential for confusion because the IKE_SA can 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.)





Eronen & Hoffman        Expires December 3, 2005               [Page 15]

Internet-Draft            IKEv2 Clarifications                 June 2005


4.  Traffic selectors

4.1  Semantics of complex traffic selector payloads

   As described in Section 3.13, the TSi/TSr payloads can include one or
   more individual traffic selectors.

   There is no requirement that TSi and TSr contain the same number of
   individual traffic selectors.  Thus, they are interpreted as follows:
   a packet matches a given TSi/TSr if it matches at least one of the
   individual selectors in TSi, and at least one of the individual
   selectors in TSr.

   For instance, 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 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 the other two combinations, cannot
   be negotiated as a single CHILD_SA pair using IKEv2.

   (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 to ICMP type and
   code fields.  As described in Section 3.13.1, "For the ICMP protocol,
   the two one octet fields Type and Code are treated as a single 16 bit
   integer (with Type in the most significant eight bits and Code in the
   least significant eight bits) port number 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 in TSr) and 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



Eronen & Hoffman        Expires December 3, 2005               [Page 16]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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 the IPv6
   mobility header [MIPv6].  However, the IKEv2 specification does not
   define how to represent the "MH Type" field 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 IPv6 mobility header message type (MH type) is placed in the most
   significant eight bits of the 16 bit local "port" selector."

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

4.4  Narrowing the traffic selectors

   Section 2.9 describes how traffic selectors are negotiated when
   creating a CHILD_SA.  A more concise summary of the narrowing process
   is presented below.

   o  If the responder's policy does not allow any part of the traffic
      covered by TSi/TSr, it responds with TS_UNACCEPTABLE.

   o  If the responder's policy allows the entire set of traffic covered
      by TSi/TSr, no narrowing is necessary, and the responder can
      return the same 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 responder narrows to an
      acceptable subset of TSi/TSr that includes TSi[1]/TSr[1].

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

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

4.5  SINGLE_PAIR_REQUIRED

   The description of the SINGLE_PAIR_REQUIRED notify payload in
   Sections 2.9 and 3.10.1 is not fully consistent.



Eronen & Hoffman        Expires December 3, 2005               [Page 17]

Internet-Draft            IKEv2 Clarifications                 June 2005


   We do not attempt to describe this payload in this document either,
   since it is expected that most implementations will not have policies
   that require separate SAs for each address pair.

   Thus, if 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
   the last two 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 this negotiation that may need some clarification is
   that when creating a new SA, the initiator should not propose traffic
   selectors that violate its own policy.  If this rule is not followed,
   valid traffic may be dropped.

   This 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, and traffic to all other hosts 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 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 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 only for
   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, 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", and (2) 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
   traffic can be unnecessarily dropped since the responder can apply
   either SA or SA' 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.)






Eronen & Hoffman        Expires December 3, 2005               [Page 18]

Internet-Draft            IKEv2 Clarifications                 June 2005


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



Eronen & Hoffman        Expires December 3, 2005               [Page 19]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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):






Eronen & Hoffman        Expires December 3, 2005               [Page 20]

Internet-Draft            IKEv2 Clarifications                 June 2005


        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))

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

        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, 0.0.0.0-255.255.255.255)

   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:

        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)

   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:





Eronen & Hoffman        Expires December 3, 2005               [Page 21]

Internet-Draft            IKEv2 Clarifications                 June 2005


        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, 192.0.2.155-192.0.2.155)

   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.




Eronen & Hoffman        Expires December 3, 2005               [Page 22]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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 containing the 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
      example in Section 2.19 is incorrect in this sense.  (Another
      interpretation would be 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 address from the network 192.0.2.0/24.  However,
      this interpretation is not supported by the IKEv2 spec.)

   This interpretation is not yet settled; and it would imply that the
   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 send copies to all other VPN clients in that address range.
   However, no implementation is known to do this, and there is nothing
   in the IKEv2 spec that would support this interpretation.

   Fortunately, Section 4 clearly says that a minimal implementation
   does not need to include or understand the INTERNAL_IP4_NETMASK
   attribute, and thus this document recommends that implementations
   should not use the INTERNAL_IP4_NETMASK attribute 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 and
   Implementation Guidelines", 2005-02-07.)

5.5  Configuration payloads for IPv6

   IKEv2 also defines configuration payloads for IPv6.  However, they
   are based on the corresponding IPv4 payloads, and do not fully follow
   the "normal IPv6 way of doing things".












Eronen & Hoffman        Expires December 3, 2005               [Page 23]

Internet-Draft            IKEv2 Clarifications                 June 2005


   A client can be assigned an IPv6 address using the
   INTERNAL_IP6_ADDRESS configuration payload.  Presumably, the idea was
   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)

        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 not used; neither is neighbor discovery.

   While this approach is reasonably simple, it has some limitations:
   IPsec tunnels configured using IKEv2 are not fully-featured
   "interfaces" in the IPv6 addressing architecture [IPv6Addr] sense.
   In particular, they do not necessarily have link-local addresses, and
   this may complicate the use of protocols that assume them, such as
   [MLDv2].  (Whether they are called "interfaces" in some particular
   operating system is 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 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 the client is assigned an IPv6
   address using the INTERNAL_IP6_ADDRESS attribute.  However, as with
   the netmask in IPv4, it is not clear what the prefix length here
   means.

   Again, one possible interpretation is 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 in [RADIUS6].  However, the previous section



Eronen & Hoffman        Expires December 3, 2005               [Page 24]

Internet-Draft            IKEv2 Clarifications                 June 2005


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

   Thus, if we assume that INTERNAL_IP4_NETMASK and the prefix length in
   INTERNAL_IP6_ADDRESS have the same meaning, and 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 address bytes it wants to use": presumably the prefix length
   tells how many low order bits there are (i.e., if the prefix length
   is X, there requester supplies 128-X low order address bits).
   However, this is quite confusing: if, say, a prefix length 126 means
   that "I want to use these 128-126=2 low order bits", why does prefix
   length 128 mean that "I want to use these 128 low order bits"?

   Another interpretation is that instead of "low order", the 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_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 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 explicit renewals are primarily useful in



Eronen & Hoffman        Expires December 3, 2005               [Page 25]

Internet-Draft            IKEv2 Clarifications                 June 2005


   environments like DHCP, where the server cannot reliably know when
   the client has gone away.  However, in IKEv2 this is known, and the
   gateway can simply free the address when the IKE_SA is deleted.

   Also, Section 4 says that supporting renewals is not mandatory.
   Given that this functionality is usually not needed, we recommend
   that gateways should not send the INTERNAL_ADDRESS_EXPIRY attribute.
   (And since this 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 the IKE_SA.

   (References: 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 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 case.

6.2  Extended Sequence Numbers (ESN) transform

   The description of the ESN transform in Section 3.3 has be proved
   difficult to understand.  When the ESN transform is included, it 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 only allowed in requests; the response
      will contain only one ESN transform.)

   In most cases, the exchange initiator will include either the first
   or third alternative in its SA payload.  The second alternative is
   rarely useful for the initiator: it means that using normal sequence



Eronen & Hoffman        Expires December 3, 2005               [Page 26]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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 "If Transform Type 5 is not included in
   a proposal, use of Extended Sequence Numbers is assumed".  Or in
   other words, omitting the ESN transform means the same thing as
   including one ESN transform with value 1.

   This choice of default value is somewhat counterintuitive and as
   described above, rarely useful.  IPsec WG decided recently to change
   this part of the specification, and make it mandatory to include the
   ESN transform for ESP/AH.

   (References: "Technical change needed to IKEv2 before publication",
   "STRAW POLL: Dealing with the ESN negotiation interop issue in 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 ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr
   payloads, IKEv2 does not require this address to match the address in
   the IP header (of IKEv2 packets), or anything in the TSi/TSr
   payloads.  The contents of IDi/IDr is used purely to fetch the policy
   and authentication data related to the other party.

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

6.4  Relationship of IKEv2 to RFC2401bis

   The IKEv2 document 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 2.24 of IKEv2 says "Specifically, tunnel encapsulators and
   decapsulators for all tunnel-mode Security Associations (SAs) created
   by IKEv2 MUST support the ECN full-functionality option for tunnels
   specified in [RFC3168] and MUST implement the tunnel encapsulation
   and decapsulation processing specified in [RFC2401bis] to prevent
   discarding of ECN congestion indications."  This, in essence, says
   that IKEv2 must be used with [RFC2401bis] only, not with RFC 2401,
   because RFC 2401 has no requirements for ECN.

6.5  Reducing the window size

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



Eronen & Hoffman        Expires December 3, 2005               [Page 27]

Internet-Draft            IKEv2 Clarifications                 June 2005


   property of a particular implementation, and is not related to
   congestion control (unlike the window size in 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 is currently in effect.  Thus, there is currently no way to
   reduce the window size of an existing IKE_SA.  However, when rekeying
   an IKE_SA, the new IKE_SA starts with window size 1 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 IKEv2 MUST be randomly chosen,
   MUST be at least 128 bits in size, and MUST be at least half the key
   size of the negotiated prf."

   However, the initiator chooses the nonce before the outcome of the
   negotiation is known.  In this case, the nonce has to be long enough
   for all the PRFs being proposed.

6.7  Initial zero octets on port 4500

   It is not clear whether a peer sending an IKE_SA_INIT request on port
   4500 should include the initial four zero octets.  Section 2.23 talks
   about how to upgrade to tunneling over port 4500 after message 2, but
   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.

       [...]

       The IKE initiator MUST check these payloads if present and if
       they do not match the addresses 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 the
       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



Eronen & Hoffman        Expires December 3, 2005               [Page 28]

Internet-Draft            IKEv2 Clarifications                 June 2005


   to do after changing to port 4500.  However, [RFC3948] shows clearly
   the format has the initial zeros even for initiators on port 4500.
   Furthermore, without the initial zeros, the processing engine cannot
   determine whether the packet is an IKE packet or an ESP packet.

   Thus, all packets sent on port 4500 need the four zero prefix;
   otherwise, the receiver won't know how to handle them.

6.8  SPI values in IKE_SA_INIT exchange

   Normal IKE messages include the 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 specification is not fully
   consistent about what values should be used.

   First, Section 3.1 says that the Responder's SPI "...MUST NOT be zero
   in any other message" (than the first message of the IKE_SA_INIT
   exchange).  However, the figure in Section 2.6 shows the second
   IKE_SA_INIT message as "HDR(A,0), N(COOKIE)", contradicting the text
   in 3.1.

   Since the responder's SPI identifies security-related state held by
   the responder, and in this case no state is created, sending a zero
   value seems reasonable.

   Second, in addition to cookies, there are several other cases when
   the IKE_SA_INIT exchange does not result in the creation of an IKE_SA
   (for instance, INVALID_KE_PAYLOAD or NO_PROPOSAL_CHOSEN).  What
   responder SPI value should be used in the IKE_SA_INIT response in
   this case?

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

   There is also an important detail about the Initiator SPI that must
   be taken into account by responders.  If a responder receives two
   IKE_SA_INIT requests with the 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 require that SPIs are chosen randomly).  Instead, the responder
   should compare the whole packets (or at the minimum, Ni payloads,
   which are always chosen randomly) to determine whether or not this
   packet creates a new IKE_SA or belongs to an existing IKE_SA.






Eronen & Hoffman        Expires December 3, 2005               [Page 29]

Internet-Draft            IKEv2 Clarifications                 June 2005


6.9  SPI values for messages outside of an IKE_SA

   The IKEv2 specification does not say what SPI values should be used
   in the IKE header for the 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
   1.5 makes it clear that these are one-way messages that must not be
   responded to.

   There are two cases when such a 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 the recipient of such a
   notification.

   A strict interpretation of the specification would require the sender
   to invent garbage values for the SPI fields.  However, we think this
   was not the 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 existing SA, this field MUST
   be sent as zero and MUST be ignored on receipt".  However, the
   specification does not clearly say which notifications are related to
   existing SAs and which are not.

   Since the main purpose of the Protocol ID field is to specify the
   type of the SPI, our interpretation is that the Protocol ID field
   should be 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 3.10.1 says that the 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 value should be included in the
   notification.  However, it is clear that the notification will be
   useful to the recipient only if it can find the IKE_SA somehow, so
   the SPI should be included.

   This still leaves two questions open: which SPI(s) should be
   included, and how it (or they) should be sent.  For the first
   question, the alternatives are the unrecognized destination SPI, the



Eronen & Hoffman        Expires December 3, 2005               [Page 30]

Internet-Draft            IKEv2 Clarifications                 June 2005


   source SPI (which presumably would be more useful for the recipient),
   or both.  For the second question, the SPI(s) could be placed in the
   SPI field(s) in the IKE header, the SPI field in the Notify payload,
   or the Notification Data field.

   In the case of another related notification, INVALID_SPI, the
   situation is clearer: there is only a single SPI, and the text
   explicitly says that the SPI is sent as Notification Data (since the
   notification is not about an existing SA, the SPI field in the Notify
   payload is not used; and obviously the value cannot be placed in the
   IKE header).

   Since the INVALID_IKE_SPI notification is sent outside of an IKE_SA,
   and it is not about an existing SA, it seems that using Notification
   Data would be the logical choice.  However, this issue needs more
   discussion and 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 "This notification asserts that this IKE_SA is the only
   IKE_SA currently active between the authenticated identities".
   However, neither Section 2.4 nor 3.10.1 says in which message this
   payload should be placed.

   The text does talk about authenticated identities, so it seems the
   notification cannot be sent before both endpoints have been
   authenticated.  Thus, the possible places are the last IKE_AUTH
   response message and a separate Informational exchange.

   Based on how this was implemented in IKEv1, it seems the intent was
   to use a separate Informational exchange.

   (References: "Clarifying the 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 state, and when
   the 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)



Eronen & Hoffman        Expires December 3, 2005               [Page 31]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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 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 pair of AUTH messages will
   have an ID of 1, the 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 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 cryptographic parts of the IKE_SA.  This might happen when the
   parties in the 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 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 sending
   endpoint will NOT accept packets that contain Flow Confidentiality
   (TFC) padding".

   However, the text does not say in which messages this notification
   should be included, or whether the scope of this notification is a
   single CHILD_SA or all CHILD_SAs of the peer.



Eronen & Hoffman        Expires December 3, 2005               [Page 32]

Internet-Draft            IKEv2 Clarifications                 June 2005


   Our interpretation is that the scope is a single CHILD_SA, and thus
   this notification is included in messages containing an SA payload
   negotiating a CHILD_SA.  If neither endpoint accepts TFC padding,
   this notification will be included in both the request proposing an
   SA and the response accepting it.  If this notification is included
   in only one of the 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 will transmit non-initial
   fragments on a tunnel mode SA that makes use of non-trivial port (or
   ICMP type/code or MH type) selectors MUST notify a peer via the IKE
   NOTIFY NON_FIRST_FRAGMENTS_ALSO payload.  The peer MUST reject this
   proposal if it will not accept non-initial fragments in this context.
   If an implementation does not successfully negotiate transmission of
   non-initial fragments for such an SA, it 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 is included
   in both the request proposing an SA and the response accepting it.
   In other words, if the peer "rejects this proposal", it only omits
   NON_FIRST_FRAGMENTS_ALSO notification from the 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
   clarifications marked with two asterisks (**) are somewhere between
   the extremes.




Eronen & Hoffman        Expires December 3, 2005               [Page 33]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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 payloads                 **



Eronen & Hoffman        Expires December 3, 2005               [Page 34]

Internet-Draft            IKEv2 Clarifications                 June 2005


      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              **
      6.18 Negotiation of NON_FIRST_FRAGMENTS_ALSO                   **

   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.

   o  Some implementations responded to a delete request by sending an
      empty INFORMATIONAL response, and then initiated their own
      INFORMATIONAL exchange with the pair of SAs to delete.

   o  Although this did not happen at the bakeoff, from the discussion
      there, it is clear 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 this document probably should address,
   but has not done so yet.




Eronen & Hoffman        Expires December 3, 2005               [Page 35]

Internet-Draft            IKEv2 Clarifications                 June 2005


   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  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  This document might want to explicitly talk about not doing ESP-
      in-AH even though it is possible.  We could say "implementations
      do not need to 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.

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),



Eronen & Hoffman        Expires December 3, 2005               [Page 36]

Internet-Draft            IKEv2 Clarifications                 June 2005


              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-06 (work
              in progress), March 2005.

13.2  Informative References

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

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

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

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

   [MIPv6]    Johnson, D., Perkins, 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.



Eronen & Hoffman        Expires December 3, 2005               [Page 37]

Internet-Draft            IKEv2 Clarifications                 June 2005


   [NAIbis]   Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
              Network Access Identifier",
              draft-ietf-radext-rfc2486bis-05 (work in progress),
              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., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RADIUS6]  Aboba, B., Zorn, 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., 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-02 (work in progress), May 2005.

   [SCVP]     Freeman, T., Housley, R., Malpani, A., Cooper, D., and T.
              Polk, "Simple Certificate Validation Protocol (SCVP)",
              draft-ietf-pkix-scvp-18 (work in progress), February 2005.


Authors' Addresses

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

   Email: pasi.eronen@nokia.com





Eronen & Hoffman        Expires December 3, 2005               [Page 38]

Internet-Draft            IKEv2 Clarifications                 June 2005


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

   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+]












Eronen & Hoffman        Expires December 3, 2005               [Page 39]

Internet-Draft            IKEv2 Clarifications                 June 2005


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+]



























Eronen & Hoffman        Expires December 3, 2005               [Page 40]

Internet-Draft            IKEv2 Clarifications                 June 2005


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)]



Eronen & Hoffman        Expires December 3, 2005               [Page 41]

Internet-Draft            IKEv2 Clarifications                 June 2005


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)]



































Eronen & Hoffman        Expires December 3, 2005               [Page 42]

Internet-Draft            IKEv2 Clarifications                 June 2005


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




Eronen & Hoffman        Expires December 3, 2005               [Page 43]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/