INTERNET-DRAFT                                                 D. Dukes
Expires March 2002                                           R. Pereira
Document: <draft-dukes-ike-mode-cfg-02.txt>               Cisco Systems
                                                         September 2001

                    The ISAKMP Configuration Method

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   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
   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at


   This document describes a new ISAKMP method that allows
   configuration items to be exchanged securely by using both
   push/acknowledge or request/reply paradigms.

   The authors currently intend this document to be published as an
   Informational RFC, not a standards-track document, so that the many
   IPsec implementations that have implemented to earlier drafts of
   this protocol can have a single stable reference.

   Comments regarding this draft should be sent to ietf-mode- or to the authors.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119 [2].

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Table of Contents
   1. Introduction....................................................3
   1.1. Changes since last revision...................................3
   1.2. Reader Prerequisites..........................................3
   2. Configuration Transaction.......................................3
   3. Configuration Method Exchange and Payload.......................4
   3.1. Transaction Exchanges.........................................4
   3.1.1. Protected Exchanges.........................................4
   3.1.2. Unprotected Exchanges.......................................5
   3.2. Attribute Payload.............................................5
   3.3. Configuration Message Types...................................6
   3.4. Configuration Attributes......................................6
   3.5. Retransmission................................................9
   4. Exchange Positioning............................................9
   5. Specific Uses...................................................9
   5.1. Requesting an Internal Address................................9
   5.2. Requesting the PeerÆs Version................................10
   6. Enterprise Management Considerations...........................11
   7. Security Considerations........................................11
   8. References.....................................................11
   10. Author's Addresses............................................12
   Full Copyright Statement..........................................13

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1. Introduction

   The ISAKMP protocol provides a framework to negotiate and generate
   Security Associations.  While negotiating SAs, it is sometimes quite
   useful to retrieve certain information from the other peer before
   the non-ISAKMP SA can be established.  Luckily, ISAKMP is also
   flexible enough to provide configuration information and do it
   securely.  This document will present a mechanism to extend ISAKMP
   to provide such functionality.

1.1. Changes since last revision.

   The last revision of this document was published as "draft-dukes-
   ike-mode-cfg-01.txt", and was originally named "draft-ietf-ipsec-

   o Fixed some typo's and cross-references.

1.2. Reader Prerequisites

   It is assumed that the reader is familiar with the terms and
   concepts described in the "Security Architecture for the Internet
   Protocol" [ArchSec] and "IP Security Document Roadmap" [Thayer97]

   Readers are advised to be familiar with both [IKE] and [ISAKMP]
   because of the terminology used within this document and the fact
   that this document is an extension of both of those documents.

2. Configuration Transaction

   A "Configuration Transaction" is defined as one or more transaction
   exchanges each consisting of two messages, the first being either a
   Set or a Request and the second being either an Acknowledge or a
   Reply, respectively.  A common identifier is used to identify the
   configuration transaction between exchanges.

   There are two paradigms to follow for this method.

   o "Request/Reply" allows a host to request information from an
   informed hosts (a configuration manager).  If the attributes in the
   Request message are not empty, then these attributes are taken as
   suggestions for that attribute.  The Reply message MAY wish to
   choose those values, or return new values.  It MAY also add new
   attributes and not include some requested attributes.

   A Reply MUST always be sent when a Request is received, even if it
   is an empty Reply or if there are missing attributes in the Request.
   This merely means that the requested attributes were not available
   or unknown.

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       Initiator              Responder
       ---------------        --------------
       REQUEST          -->
                        <--   REPLY

   o "Set/Acknowledge" works on the push principle that allows a
   configuration manager (a host that wishes to send information to
   another host) to start the configuration transaction.  This code
   sends attributes that it wants the peer to alter.  The Acknowledge
   code MUST return the zero length attributes that it accepted.  Those
   attributes that it did not accept will NOT be sent back in the

       Initiator              Responder
       ---------------        -------------------
       SET              -->
                        <--   ACKNOWLEDGE

   Transaction exchanges are completed once the Reply or Acknowledge
   code is received.  If one is not received, the implementation MAY
   wish to retransmit the original message as detailed in a later

   The initiator and responder are not necessarily the same as the
   initiator and responder of the ISAKMP exchange.

3. Configuration Method Exchange and Payload

3.1. Transaction Exchanges

   A new exchange mode is required for the configuration method.  This
   exchange is called the "Transaction Exchange" and has a value of 6.
   This exchange is quite similar to the Information exchange described
   in [ISAKMP] and [IKE], but allows for multi-exchange transactions
   instead of being a one-way transmittal of information.

   This specification protects ISAKMP Transaction Exchanges when

3.1.1. Protected Exchanges

   Once an ISAKMP security association has been established (and
   SKEYID_e and SKEYID_a have been generated), the ISAKMP Transaction
   Exchange is as follows:

        Initiator                        Responder
       -----------                      -----------
        HDR*, HASH, ATTR      -->
                              <--        HDR*, HASH, ATTR

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   Where the HASH payload contains the prf output, using SKEYID_a as
   the key, and the M-ID (ISAKMP header Message ID) unique to this
   exchange concatenated with all of the payloads after the HASH
   payload. In other words, the hash for the above exchange is:

       HASH = prf( SKEYID_a, M-ID | ATTR )

   Multiple ATTR payloads MAY NOT be present in the Transaction

   As noted, the message ID in the ISAKMP header-- as used in the prf
   computation-- is unique to this transaction exchange and MUST NOT be
   the same as the message ID of another transaction exchange.  The
   derivation of the initialization vector (IV) for the first message,
   used with SKEYID_e to encrypt the message, is described in Appendix
   B of [IKE].  Subsequent IVs are taken from the last ciphertext block
   of the previous message as described in [IKE].

3.1.2. Unprotected Exchanges

   If the ISAKMP security association has not yet been established at
   the time of the Transaction Exchange and the information being
   exchanged is not sensitive, the exchange MAY be done in the clear
   without an accompanying HASH payload.

        Initiator                        Responder
       -----------                      -----------
        HDR, ATTR           -->
                            <--          HDR, ATTR

   Multiple ATTR payloads MAY NOT be present in the Transaction

3.2. Attribute Payload

   A new payload is defined to carry attributes as well as the type of
   transaction message.

                           1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     ! Next Payload  !   RESERVED    !         Payload Length        !
     !     Type      !   RESERVED    !           Identifier          !
     !                                                               !
     ~                           Attributes                          ~
     !                                                               !

   The Attributes Payload fields are defined as follows:

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   o Next Payload (1 octet) - Identifier for the payload type of the
   next payload in the message.  If the current payload is the last in
   the message, then this field will be 0.

   o RESERVED (1 octet) - Unused, set to 0.

   o Payload Length (2 octets) - Length in octets of the current
   payload, including the generic payload header, the transaction-
   specific header and all attributes.  If the length does not match
   the length of the payload headers plus the attributes, (i.e. an
   attribute is half contained within this payload) then entire payload
   MUST be discarded.

   o Attribute Message Type (1 octet) - Specifies the type of message
   represented by the attributes.  These are defined in the next

   o RESERVED (1 octet) - Unused, set to 0.

   o Identifier (2 octets) - An identifier used to reference a
   configuration transaction within the individual messages.

   o Attributes (variable length) - Zero or more ISAKMP Data Attributes
   as defined in [ISAKMP].  The attribute types are defined in a later

   The payload type for the Attributes Payload is 14.

3.3. Configuration Message Types

   These values are to be used within the Type field of an Attribute
   ISAKMP payload.

    Types                      Value
   ========================== ===========
    RESERVED                   0
    ISAKMP_CFG_REQUEST         1
    ISAKMP_CFG_REPLY           2
    ISAKMP_CFG_SET             3
    ISAKMP_CFG_ACK             4
    Reserved for Future Use    5-127
    Reserved for Private Use   128-255

   Messages with unknown types SHOULD be silently discarded.

3.4. Configuration Attributes

   Zero or more ISAKMP attributes [ISAKMP] are contained within an
   Attributes Payload. Zero length attribute values are usually sent in
   a Request and MUST NOT be sent in a Response.

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   All IPv6 specific attributes are mandatory only if the
   implementation supports IPv6 and vice versa for IPv4.  Mandatory
   attributes are stated below.

   Unknown private attributes SHOULD be silently discarded.

   The following attributes are currently defined:

    Attribute                 Value   Type       Length
   ========================= ======= ========== =====================
    RESERVED                    0
    INTERNAL_IP4_ADDRESS        1     Variable   0 or 4 octets
    INTERNAL_IP4_NETMASK        2     Variable   0 or 4 octets
    INTERNAL_IP4_DNS            3     Variable   0 or 4 octets
    INTERNAL_IP4_NBNS           4     Variable   0 or 4 octets
    INTERNAL_ADDRESS_EXPIRY     5     Variable   0 or 4 octets
    INTERNAL_IP4_DHCP           6     Variable   0 or 4 octets
    APPLICATION_VERSION         7     Variable   0 or more
    INTERNAL_IP6_ADDRESS        8     Variable   0 or 16 octets
    INTERNAL_IP6_NETMASK        9     Variable   0 or 16 octets
    INTERNAL_IP6_DNS           10     Variable   0 or 16 octets
    INTERNAL_IP6_NBNS          11     Variable   0 or 16 octets
    INTERNAL_IP6_DHCP          12     Variable   0 or 16 octets
    INTERNAL_IP4_SUBNET        13     Variable   0 or 8 octets
    SUPPORTED_ATTRIBUTES       14     Variable   0 or multiples of 2
    INTERNAL_IP6_SUBNET        15     Variable   0 or 17 octets
    Reserved for future use    16-16383
    Reserved for private use   16384-32767

   o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - Specifies an address
   within the internal network.  This address is sometimes called a red
   node address or a private address and MAY be a private address on
   the Internet.  Multiple internal addresses MAY be requested by
   requesting multiple internal address attributes.  The responder MAY
   only send up to the number of addresses requested.

   The requested address is valid until the expiry time defined with
   the INTERNAL_ADDRESS EXPIRY attribute or until the ISAKMP SA that
   was used to secure the request expires.  The address MAY also expire
   when the IPSec (phase 2) SA expires, if the request is associated
   with a phase 2 negotiation.  If no ISAKMP SA was used to secure the
   request, then the response MUST include an
   expiry or the host MUST expire the SA after an implementation-
   defined time.

   An implementation MUST support this attribute.

   network's netmask.  Only one netmask is allowed in the request and
   reply messages (e.g. and it MUST be used only with an
   INTERNAL_ADDRESS attribute.

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   An implementation MUST support this attribute.

   o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a DNS
   server within the network.  Multiple DNS servers MAY be requested.
   The responder MAY respond with zero or more DNS server attributes.

   o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of a
   NetBios Name Server (WINS) within the network.  Multiple NBNS
   servers MAY be requested.  The responder MAY respond with zero or
   more NBNS server attributes.

   o INTERNAL_ADDRESS_EXPIRY - 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 attribute MAY be present
   in the reply.

   An implementation MUST support this attribute.

   o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to send
   any internal DHCP requests to the address contained within the
   attribute.  Multiple DHCP servers MAY be requested.  The responder
   MAY respond with zero or more DHCP server attributes.

   o APPLICATION_VERSION - The version or application information of
   the IPSec host.  This is a string of printable ASCII characters that
   is NOT null terminated.

   This attribute does not need to be secured.

   An implementation MUST support this attribute.

   o INTERNAL_IP4_SUBNET - The protected sub-networks that this edge-
   device protects.  This attribute is made 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.

   An implementation MUST support this attribute.

   o SUPPORTED_ATTRIBUTES - When used within a Request, this attribute
   must be zero length and specifies a query to the responder to reply
   back with all of the attributes that it supports.  The response
   contains an attribute that contains a set of attribute identifiers
   each in 2 octets.  The length divided by 2 (bytes) would state the
   number of supported attributes contained in the response.

   An implementation MUST support this attribute.

   o INTERNAL_IP6_SUBNET - The protected sub-networks that this edge-
   device protects.  This attribute is made up of two fields; the first
   being a 16 octet IPv6 address the second being a one octet prefix-
   mask as defined in [ADDRIPV6].  Multiple sub-networks MAY be

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                   The ISAKMP Configuration Method     September 2001

   requested.  The responder MAY respond with zero or more sub-network

   An implementation MUST support this attribute.

   Note that no recommendations are made in this document how an
   implementation actually figures out what information to send in a
   reply.  i.e. we do not recommend any specific method of (an edge
   device) determining which DNS server should be returned to a
   requesting host.

3.5. Retransmission

   Retransmission SHOULD follow the same retransmission rules used with
   standard ISAKMP messages.

4. Exchange Positioning

   The exchange and messages defined within this document MAY appear at
   any time.  Because of security considerations with most attributes,
   the exchange SHOULD be secured with an ISAKMP phase 1 SA.

   Depending on the type of transaction and the information being
   exchanged, the exchange MAY be dependant on an ISAKMP phase 1 SA
   negotiation, a phase 2 SA negotiation, or none of the above.

   The next section details specific functions and their position
   within an ISAKMP negotiation.

5. Specific Uses

   The following descriptions detail how to perform specific functions
   using this protocol.  Other functions are possible and thus this
   list is not a complete list of all of the possibilities.  While
   other functions are possible, the functions listed below MUST be
   performed as detailed in this document to preserve interoperability
   among different vendor's implementations.

5.1. Requesting an Internal Address

   This function provides address allocation to a remote host trying to
   tunnel into a network protected by an edge device.   The remote host
   requests an address and optionally other information concerning the
   internal network from the edge device.  The edge device procures an
   internal address for the remote host from any number of sources such
   as a DHCP/BOOTP server or its own address pool.

    Initiator                           Responder
   -----------------------------       -------------------------------

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    HDR*, HASH, ATTR1(REQUEST)    -->
                                  <--   HDR*, HASH, ATTR2(REPLY)
    ATTR1(REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute
   (either IPv4 or IPv6) but MAY also contain any number of additional
   attributes that it wants returned in the response.

   For example:


   All returned values will be implementation dependent.  As can be
   seen in the above example, the edge device MAY also send other
   attributes that were not included in the REQUEST and MAY ignore the
   non-mandatory attributes that it does not support.

   This Transaction Exchange MUST occur after an ISAKMP phase 1 SA is
   already established and before an ISAKMP phase 2 negotiation has
   started, since that negotiation requires the internal address.

   Initial Negotiation:
     MainMode or AggressiveMode
     TransactionMode (IP Address request)

   Subsequent address requests would be done without the phase 1
   negotiation when there already exists a phase 1 SA.

   Subsequent Negotiations:
     TransactionMode (IP Address request)

5.2. Requesting the Peer's Version

   An IPSec host wishing to inquire about the other peer's version
   information (with or without security) MUST use this method.

    Initiator                           Responder
   -----------------------------       --------------------------
    HDR, ATTR1(REQUEST)           -->
                                  <--   HDR, ATTR2(REPLY)


     APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar Inc.")

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   The return text string will be implementation dependent.  This
   transaction MAY be done at any time and with or without any other
   ISAKMP exchange and because the version information MAY be deemed
   not sensitive, security is optional.

6. Enterprise Management Considerations

   The method defined in this document SHOULD NOT be used for wide
   scale management.  Its main intent is to provide a bootstrap
   mechanism to exchange information within IPSec.  While it MAY be
   useful to use such a method of exchange information to some outlying
   IPSec hosts or small networks, existing management protocols such as
   considered for enterprise management as well as subsequent
   information exchanges.

7. Security Considerations

   This entire draft discusses a new ISAKMP configuration method to
   allow IPSec-enabled entities to acquire and share configuration

   The draft mandates that this exchange should normally occur after
   the Phase I Security Association has been set up and that the entire
   exchange be protected by that Phase I SA.  Thus the exchange is as
   secure as any Phase II SA negotiation.

   This exchange MAY be secured (encrypted and authenticated) by other
   means as well, such as pre-configured ESP [ESP] or data-link

8. References

   [1]         Bradner, S., "The Internet Standards Process -- Revision
               3", BCP 9, RFC 2026, October 1996.

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

   [Thayer97]  R. Thayer, N. Doraswamy, R. Glenn. "IP Security Document
               Roadmap", RFC2411

   [ArchSec]   S. Kent, R. Atkinson, "Security Architecture for the
               Internet Protocol", RFC2401

   [ISAKMP]    D. Maughan, M. Schertler, M. Schneider, J. Turner,
               "Internet Security Association and Key Management
               Protocol", RFC2408

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                   The ISAKMP Configuration Method     September 2001

   [IKE]       D. Harkins, D. Carrel, "The Internet Key Exchange
               (IKE)", RFC2409

   [DHCP]      R. Droms, "Dynamic Host Configuration Protocol",

   [RADIUS]    C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote
               Authentication Dial In User Service (RADIUS)", RFC2138

   [LDAP]      M. Wahl, T. Howes, S. Kille., "Lightweight Directory
               Access Protocol (v3)", RFC2251

   [ESP]       S. Kent, "IP Encapsulating Security Payload (ESP)",

   [ADDRIPV6]  Hinden, R., "IP Version 6 Addressing Architecture",
               RFC 2373, July 1998.

9. Acknowledgments

   The editors would like to thank Sanjay Anand, Baiju V. Patel,
   Stephane Beaulieu, Tim Jenkins, Peter Ford, Bob Moskowitz and Shawn

10. Author's Addresses

   Darren Dukes
   Cisco Systems Co.
   365 March Road
   Kanata, ON, Canada
   Phone: 1-613-271-3679

   Roy Pereira
   Cisco Systems, Inc.
   170 Tasman Drive
   San Jose, CA, USA
   Phone: 1-408-526-6793

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                   The ISAKMP Configuration Method     September 2001

Full Copyright Statement

   "Copyright (C) The Internet Society (date). All Rights Reserved.
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into

   This Internet Draft expires September 2001

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