Internet Engineering Task Force R. Pereira, TimeStep Corp.
IP Security Working Group S. Anand, Microsoft Corp.
Internet Draft B. Patel, Intel Corp.
Expires in six months
August 17, 1999
The ISAKMP Configuration Method
<draft-ietf-ipsec-isakmp-mode-cfg-05.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document describes a new ISAKMP method that allows
configuration items to be exchanged securely by using both
push/acknowledge or request/reply paradigms.
R. Pereira, S. Anand, B. Patel [Page 1]
Internet Draft The ISAKMP Configuration Method August, 99
Table of Contents
1. Introduction..............................................2
1.1 Reader Prerequisites......................................2
1.2 Specification of Requirements.............................3
2. Configuration Transaction.................................3
3. Configuration Method Exchange and Payload.................4
3.1 Transaction Exchanges.....................................4
3.2 Attribute Payload.........................................5
3.3 Configuration Message Types...............................6
3.4 Configuration Attributes..................................7
3.5 Retransmission............................................9
4. Exchange Positioning......................................9
5. Specific Uses.............................................9
5.1 Requesting an Internal Address...........................10
5.2 Requesting the Peer's Version............................11
6. Enterprise Management Considerations.....................11
7. Security Considerations..................................11
8. References...............................................12
9. Acknowledgments..........................................12
10. Editors' Addresses.......................................13
11. Expiration...............................................13
12. Full Copyright Statement.................................14
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 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]
documents.
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.
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1.2 Specification of Requirements
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", and "MAY" that appear in this document are to be interpreted
as described in [Bradner97].
2. Configuration Transaction
A "Configuration Transaction" is defined as two configuration
exchanges, 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 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.
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 acknowledgement.
Initiator Responder
--------------- -------------------
SET -->
<-- ACKNOWLEDGE
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Transactions are completed once the Reply or Acknowledge code is
received. If one is not received, the implementation MAY wish to
retransmit the original exchange as detailed in a later section.
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
possible.
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
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
Exchange.
As noted, the message ID in the ISAKMP header-- as used in the prf
computation-- is unique to this exchange and MUST NOT be the same
as the message ID of another 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
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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
Exchange.
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:
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.
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o Attribute Message Type (1 octet) - Specifies the type of message
represented by the attributes. These are defined in the next
section.
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 section.
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.
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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.
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 4 octets
SUPPORTED_ATTRIBUTES 14 Variable 0 or multiples of 2
Reserved for future use 15-16383
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
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expiry or the host MUST expire the SA after an implementation-
defined time.
An implementation MUST support this attribute.
o INTERNAL_IP4_NETMASK, INTERNAL_IP6_NETMASK - The internal
network's netmask. Only one netmask is allowed in the request
and reply messages. (e.g. 255.255.255.0)
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 û The protected sub-networks that this edge-
device protects. Multiple sub-networks MAY be requested. The
responder MAY respond with zero or more sub-networks attributes.
An implementation MUST support this attribute.
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o SUPPORTED_ATTRIBUTES û 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.
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.
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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 an its own address
pool.
Initiator Responder
----------------------------- -------------------------------
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:
ATTR1(REQUEST) =
INTERNAL_ADDRESS(0.0.0.0)
INTERNAL_NETMASK(0.0.0.0)
INTERNAL_DNS(0.0.0.0)
ATTR2(REPLY) =
INTERNAL_ADDRESS(192.168.219.202)
INTERNAL_NETMASK(255.255.255.0)
INTERNAL_SUBNET(291.168.219.0/255.255.255.0)
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)
QuickMode(s)
Subsequent address requests would be done without the phase 1
negotiation when there already exists a phase 1 SA.
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Subsequent Negotiations:
TransactionMode (IP Address request)
QuickMode(s)
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)
ATTR1(REQUEST) =
APPLICATION_VERSION("")
ATTR2(REPLY) =
APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar Inc.")
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 DHCP [DHCP], RADIUS [RADIUS], SNMP or LDAP [LDAP]
should be 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
information.
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
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means as well, such as pre-configured ESP or data-link security.
8. References
[ArchSec] S. Kent, R. Atkinson, "Security Architecture for the
Internet Protocol", RFC2401
[Bradner97] S. Bradner, "Key words for use in RFCs to indicate
Requirement Levels", RFC2119
[ISAKMP] D. Maughan, M. Schertler, M. Schneider, J. Turner,
"Internet Security Association and Key Management
Protocol", RFC2408
[IKE] D. Harkins, D. Carrel, "The Internet Key Exchange
(IKE)", RFC2409
[DHCP] R. Droms, "Dynamic Host Configuration Protocol",
RFC2131
[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)",
RFC2406
9. Acknowledgments
The editors would like to thank Stephane Beaulieu, Tim Jenkins,
Peter Ford, Bob Moskowitz and Shawn Mamros.
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10. Editors' Addresses
Roy Pereira
rpereira@timestep.com
TimeStep Corporation
+1 (613) 599-3610 x 4808
Sanjay Anand
sanjayan@microsoft.com
Microsoft Corporation
+1 (206) 936-6367
Baiju V. Patel
baiju@mailbox.jf.intel.com
Intel Corporation
+1 (503) 264 2422
The IPSec working group can be contacted via the IPSec working
group's mailing list (ipsec@tis.com) or through its chairs:
Robert Moskowitz
rgm@icsa.net
International Computer Security Association
Theodore Y. Ts'o
tytso@mit.edu
Massachusetts Institute of Technology
11. Expiration
This draft expires January 17, 2000.
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12. Full Copyright Statement
Copyright (C) The Internet Society (1998). 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 languages
other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS 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.
R. Pereira, S. Anand, B. Patel [Page 14]
