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
February 12, 1998
The ISAKMP Configuration Method
<draft-ietf-ipsec-isakmp-mode-cfg-02.txt>
Status of this Memo
This document is a submission to the IETF Internet Protocol
Security (IPSECond) Working Group. Comments are solicited and
should be addressed to the working group mailing list
(ipsec@tis.com) or to the editor.
This document is an Internet-Draft. Internet Drafts are working
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Distribution of this memo is unlimited.
Abstract
This document describes a new ISAKMP method that allows information
like configuration items to be exchanged securely by using both
push/acknowledge or request/reply paradigms.
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Internet Draft The ISAKMP Configuration Method February, 98
Table of Contents
1. Introduction...................................................2
1.1. Specification of Requirements..............................2
2. Configuration And Information Method...........................3
3. Configuration Transaction......................................3
3.1. Configuration NOTIFY Codes.................................4
3.2. Configuration NOTIFY Data And Attributes...................5
3.3. Retransmission.............................................6
4. Examples.......................................................6
5. Enterprise Management Considerations...........................8
6. Security Considerations........................................8
7. References.....................................................9
8. Acknowledgments................................................9
9. Editors' Addresses.............................................9
1. Introduction
ISAKMP provides a framework to negotiate and derive Security
Associations, but since it is used within the IPSec framework it
may also be used to configure or retrieve information from secure
hosts. This configuration may take place between a gateway, an
end-host client, or a configuration manager. For example, this can
be used to configure multi-protocol IP tunnels securely.
It is assumed that the reader is familiar with the terms and
concepts described in the "Security Architecture for the Internet
Protocol" [Atkinso95] and "IP Security Document Roadmap" [Thayer97]
documents.
Readers are advised to be familiar with both [Harkins97] and
[ISAKMP] because of the terminology used within this document and
the fact that this document is an extension of both of those
documents.
1.1. 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].
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2. Configuration And Information Method
The premise behind this method is to utilize the existing ISAKMP
protocol as much as possible to build more functionality. The
Configuration and Information method described in this document
uses the ISAKMP NOTIFY payload to transfer information between two
hosts. Within the ISAKMP NOTIFY payload are ISAKMP attributes that
relay the actual information.
Depending on the type of information relayed by the exchange, it
MIGHT have to be secured. For example, if password information
were being exchanged, then the exchange would be REQUIRED to be
secured (both encrypted and authenticated).
The NOTIFY payload MAY be sent within an ISAKMP exchange (like Main
Mode or Aggressive Mode) or by itself. When sent by itself, it
MUST be sent in an Info Mode exchange.
If security is required for the attributes being exchanged, and the
exchange is occurring in an Info Mode ISAKMP exchange, then
security is exactly as defined in [Harkins97] under the section
entitled "ISAKMP Information Exchanges".
3. Configuration Transaction
A "Configuration Transaction" is defined as two Configuration
Method exchanges, the first being either a Set or a Request and the
second being either a Acknowledge or a Reply respectively. The SPI
within the ISAKMP NOTIFY payload header identifies the
configuration transaction. A SPI length of 4 octets SHOULD be
sufficient, but any length greater than zero MUST be supported and
returned in the reply and acknowledgement.
There are two paradigms to follow for this method.
o "Set/Acknowledge" works on the push principle that allows a
configuration manager (a host that wishes to send information to
another) 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
--------------- -------------------
NOTIFY(SET) -->
<-- NOTIFY(ACKNOWLEDGE)
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o "Request/Reply" allows a host to request information from an
informed host (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.
Initiator Responder
--------------- --------------
NOTIFY(REQUEST) -->
<-- NOTIFY(REPLY)
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.
The initiator and responder MAY not be the same as the initiator
and responder of the ISAKMP exchange.
If a badly formatted exchange is received, the message SHOULD be
silently discarded and perhaps logged locally, as per local policy.
Badly formatted exchanges MIGHT also include those with unknown
codes or unknown attributes within the Configuration Method.
3.1. Configuration NOTIFY Codes
Code Value
========================== ===========
ISKAMP_CFG_REQUEST 101
ISKAMP_CFG_REPLY 102
ISKAMP_CFG_SET 103
ISKAMP_CFG_ACK 104
Since the Configuration Method uses NOTIFY codes for information
exchange, if the peer does not support this functionality, it will
quietly discard the message without breaking.
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3.2. Configuration NOTIFY Data And Attributes
Zero or more ISAKMP attributes [ISAKMP] make up the NOTIFY
payloads data. The following attributes are defined to be valid
within the payload:
Attribute Value Type Length
====================== ======= ================ ===================
INTERNAL_ADDRESS 1 Variable 0 or 4 octets
INTERNAL_NETMASK 2 Variable 0 or 4 octets
INTERNAL_DNS 3 Variable 0 or 4 octets
INTERNAL_NBNS 4 Variable 0 or 4 octets
INTERNAL_ADDRESS_EXPIRY 5 Basic/Variable 0 or 2 or 4 octets
INTERNAL_DHCP 6 Variable 0 or 4 octets
APPLICATION_VERSION 7 Variable variable
Reserved for future use 8-16383
Private use 16384-32767
o INTERNAL_ADDRESS - Specifies an IPv4 address within the internal
network. This address is sometimes called a red node address or
a private address and MAY be an illegal address on the Internet.
Multiple internal addresses MAY be requested. The responder MAY
only send up to the number of addresses requested.
The requested address is valid until the expiry time, or until
the ISAKMP SA that was used to secure the request, expires. If
no ISAKMP SA was used to secure the request, then the response
MUST include an expiry.
o INTERNAL_NETMASK - The internal network's netmask. Only one
netmask is allowed in the request and reply messages. (eg.
255.255.255.0)
o INTERNAL_DNS - Specifies an IPv4 address of a DNS server within
the network. Multiple DNS servers MAY be requested. The
responder MAY respond with any number of DNS server attributes.
o INTERNAL_NBNS - Specifies an IPv4 address of a NetBios Name
Server (WINS) within the network. Multiple NBNS servers MAY be
requested. The responder MAY respond with any number of 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.
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o INTERNAL_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 any number of DHCP server attributes.
o APPLICATION_VERSION - The version or application information of
the IPSec host. This is a string of printable ASCII characters
that MIGHT NOT be null delimited. This attributed does NOT need
to be secured.
It is hoped that more attribute types will be defined in the
future. Some suggestions would be to distribute local policy, or
even authenticate certificates. Also, note that no recommendations
are made to how an implementation actually figures out what
information to send. i.e. we do not recommend any specific method
of (a gateway) determining which DNS server should be returned to a
requesting host.
3.3. Retransmission
Retransmission of Configuration messages SHOULD follow the same
retransmission rules used with standard ISAKMP messages.
While a response does not have to be sent in the next ISAKMP
message, it SHOULD be made within a time period. If a response is
not received within that time period, the initiator MIGHT
retransmit the same request.
4. Examples
Some examples of positioning this configuration method follow.
These are meant only as examples and should not be thought of as
the only possibilities for this protocol.
Example 1: Initiator requesting his internal IP address during the
last exchange in Main Mode using the shared secret authentication
method.
Initiator Responder
----------------------------- --------------------------------
HDR(Main), SA -->
<-- HDR(Main), SA
HDR(Main), KEY, Ni -->
<-- HDR(Main), KEY, Nr
HDR(Main)*,ID,HASH,NOTIFY(REQUEST) -->
<-- HDR(Main)*,ID,HASH,NOTIFY(REPLY)
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REQUEST =
INTERNAL_ADDRESS(0.0.0.0),
INTERNAL_NETMASK(0.0.0.0),
INTERNAL_DNS(0.0.0.0)
REPLY =
INTERNAL_ADDRESS(192.168.219.202),
INTERNAL_NETMASK(255.255.255.0),
INTERNAL_DNS(291.168.219.4)
Please note that the responder MAY have sent the reply within the
Main Mode exchange as well as sending the reply by itself using
InfoMode;
HDR(Main)*,ID,HASH,NOTIFY(REQUEST) -->
<-- HDR(Main)*, ID, HASH
<-- HDR(Info)*, NOTIFY(REPLY)
Or the initiator could have sent the request in an InfoMode message
after MainMode completed.
If another tunneled SA is negotiated with this ISAKMP SA and an
internal IP address is required, then the initiator would perform
the request through a InfoMode request before the QuickMode
negotiation.
Initiator Responder
----------------------------- --------------------------
HDR(Info)*, NOTIFY(REQUEST) -->
<-- HDR(Info)*, NOTIFY(REPLY)
Example 2: A central configuration manager application sends out
some information to an IPSec host.
Initiator Responder
----------------------------- --------------------------
HDR(Info)*, NOTIFY(SET) -->
<-- HDR(Info)*, NOTIFY(ACK)
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Internet Draft The ISAKMP Configuration Method February, 98
Example 3: An IPSec host inquires about the peer's version
information (without security).
Initiator Responder
----------------------------- --------------------------
HDR(Info), NOTIFY(REQUEST) -->
<-- HDR(Info), NOTIFY(REPLY)
REQUEST = APPLICATION_VERSION("")
REPLY = APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar Inc.")
Example 4: Same as Example 1, but using Aggressive Mode (Aggr).
Notice how the replay comes back secured since Aggressive Mode has
completed and created an ISAKMP SA.
Initiator Responder
------------------------------- --------------------------
HDR(Aggr), SA, KE, N, ID -->
<-- HDR(Aggr), SA, KE, N, ID, HASH
HDR(Aggr), HASH, NOTIFY(REQUEST) -->
<-- HDR(Info)*, NOTIFY(REPLY)
5. 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 [Droms97], RADIUS [Radius], SNMP or LDAP
[Ldap97] should be considered for enterprise management as well as
subsequent information exchanges.
6. 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
means as well, such as pre-configured ESP or data-link security.
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7. References
[Atkinso95] R. Atkinson, "Security Architecture for the Internet
Protocol", draft-ietf-ipsec-arch-sec-01
[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", draft-ietf-ipsec-isakmp-08
[Harkins97] D. Harkins, "The Resolution of ISAKMP and Oakley",
draft-ietf-ipsec-isakmp-oakley-05
[Droms97] R. Droms, "Dynamic Host Configuration Protocol",
RFC2131
[Radius97] C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote
Authentication Dial In User Service (RADIUS)", RFC2138
[Ldap97] M. Wahl, T. Howes, S. Kille., "Lightweight Directory
Access Protocol (v3)", RFC2251
8. Acknowledgments
The editors would like to thank Tim Jenkins, Peter Ford, Bob
Moskowitz and Shawn Mamros.
9. 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
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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
R. Pereira, S. Anand, B. Patel [Page 10]
