draft-ietf-dhc-vpn-option-03.txt   draft-ietf-dhc-vpn-option-04.txt 
Network Working Group R. Johnson
Internet-Draft J. Kumarasamy
Expires: August 10, 2005 K. Kinnear
M. Stapp
Cisco
February 9, 2005
Internet Engineering Task Force Richard Johnson Virtual Subnet Selection Option
Internet Draft Kim Kinnear draft-ietf-dhc-vpn-option-04.txt
Expiration: March 2005 Mark Stapp
File: draft-ietf-dhc-vpn-option-03.txt Jay Kumarasamy
Cisco Systems, Inc.
DHCP VPN Information option
<draft-ietf-dhc-vpn-option-03.txt>
September 27, 2004
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2005).
Abstract Abstract
This memo defines a new DHCP option for passing VPN information This memo defines a new DHCP option for passing Virtual Subnet
between the DHCP client and the DHCP server. It is intended for use Selection (VSS) information between the DHCP client and the DHCP
primarily by DHCP proxy clients in situations where VPN information server. It is intended for use primarily by DHCP proxy clients in
needs to be passed to the DHCP server for proper address allocation situations where VSS information needs to be passed to the DHCP
to take place. server for proper address allocation to take place.
1.0 Introduction The option number currently in use is 221. This memo documents the
current usage of the option in agreement with RFC-3942[7] , which
declares that any pre-existing usages of option numbers in the range
128 - 223 should be documented and the working group will try to
officially assign those numbers to those options.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. VSS Information Definition . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . 10
1. Introduction
There is a growing use of Virtual Private Network (VPN) There is a growing use of Virtual Private Network (VPN)
configurations. The growth comes from many areas; individual client configurations. The growth comes from many areas; individual client
systems needing to appear to be on the home corporate network even systems needing to appear to be on the home corporate network even
when traveling, ISPs providing extranet connectivity for customer when traveling, ISPs providing extranet connectivity for customer
companies, etc. In some of these cases there is a need for the DHCP companies, etc. In some of these cases there is a need for the DHCP
server to know the VPN from which an address, and other resources, server to know the VPN (hereafter called a "Virtual Subject Selector"
should be allocated. or "VSS") from which an address, and other resources, should be
allocated.
If the allocation is being done through a DHCP relay, then a relay If the allocation is being done through a DHCP relay, then a relay
suboption could be included. In some cases, however an IP address is suboption could be included. In some cases, however an IP address is
being sought by a DHCP proxy on behalf of a client (would may be being sought by a DHCP proxy on behalf of a client (would may be
assigned the address via a different protocol). In this case, there assigned the address via a different protocol). In this case, there
is a need to include VPN information relating to the client as a DHCP is a need to include VSS information relating to the client as a DHCP
option. option.
A good example might be a dial-in aggregation device where PPP A good example might be a dial-in aggregation device where PPP
addresses are acquired via DHCP and then given to the remove customer addresses are acquired via DHCP and then given to the remove customer
system via IPCP. In a network where such a device is used to system via IPCP. In a network where such a device is used to
aggregate PPP dial-in from multiple companies, each company may be aggregate PPP dial-in from multiple companies, each company may be
assigned a unique VPN. assigned a unique VSS.
This memo defines a new DHCP [2] option, the VPN Information option, This memo defines a new DHCP [2] option, the VSS Information option,
which allows the DHCP client to specify the VPN Information needed in which allows the DHCP client to specify the VSS Information needed in
order to allocate an address. If the receiving DHCP server order to allocate an address. If the receiving DHCP server
understands the VPN Information option, this information may be used understands the VSS Information option, this information may be used
in conjunction with other information in determining the subnet on in conjunction with other information in determining the subnet on
which to select an address as well as other information such as DNS which to select an address as well as other information such as DNS
server, default router, etc. server, default router, etc.
1.1 Conventions 2. VSS Information Definition
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [3].
2.0 VPN Information Option Definition
The VPN Information option is a DHCP option [3]. The option contains The VSS Information option is a DHCP option [3]. The option contains
generalized VPN information in one of two formats: NVT ASCII VPN generalized VSS information in one of two formats: NVT ASCII VPN
identifier, or RFC2685 VPN-ID [4]. identifier, or RFC2685 VPN-ID [4].
The format of the option is: The format of the option is:
Code Len Type VPN Information octets Code Len Type VSS Information octets
+-----+-----+------+-----+-----+-----+--- +-----+-----+------+-----+-----+-----+---
| TBD | n | t | v1 | v2 | v3 | ... | 221 | n | t | v1 | v2 | v3 | ...
+-----+-----+------+-----+-----+-----+--- +-----+-----+------+-----+-----+-----+---
Type: 0 NVT ASCII VPN identifier Type: 0 NVT ASCII VPN identifier
1 RFC2685 VPN-ID 1 RFC2685 VPN-ID
2-255 Not Allowed 2-255 Not Allowed
Figure 1
The option minimum length (n) is 2. The option minimum length (n) is 2.
There are two types of identifiers which can be placed in the VPN There are two types of identifiers which can be placed in the VSS
Information Option. The first type of identifier which can be placed Information Option. The first type of identifier which can be placed
in the VPN Information Option is an NVT ASCII string. It MUST NOT be in the VSS Information Option is an NVT ASCII string. It MUST NOT be
terminated with a zero byte. terminated with a zero byte.
The second type of identifier which can be placed in the VPN The second type of identifier which can be placed in the VSS
Information Option is an RFC2685 VPN-ID [4], which is typically 14 Information Option is an RFC2685 VPN-ID [4], which is typically 14
hex digits in length (though it can be any length as far as the VPN hex digits in length (though it can be any length as far as the VSS
Information Option is concerned). Information Option is concerned).
If the type field is set to zero (0), it indicates that all following If the type field is set to zero (0), it indicates that all following
bytes of the option contain a NVT ASCII string. This string MUST NOT bytes of the option contain a NVT ASCII string. This string MUST NOT
be terminated with a zero byte. be terminated with a zero byte.
If the type field is set to one (1), it indicates that all following If the type field is set to one (1), it indicates that all following
bytes should be interpreted in agreement with [4] as a VPN bytes should be interpreted in agreement with [4] as a VPN
Identifier, typically 14 hex digits. Identifier, typically 14 hex digits.
All other values of the type field are invalid as of this memo and All other values of the type field are invalid as of this memo and
VPN options containing any other value than zero (0) or one (1) VSS options containing any other value than zero (0) or one (1)
SHOULD be ignored. SHOULD be ignored.
Any VPN information contained in a DHCP Relay Suboption SHOULD Any VSS information contained in a DHCP Relay Suboption SHOULD
override the information contained in this VPN Information option. override the information contained in this VSS Information option
Servers configured to support this option MUST return an identical Servers configured to support this option MUST return an identical
copy of the option to any client that sends it, regardless of whether copy of the option to any client that sends it, regardless of whether
or not the client requests the option in a parameter request list. or not the client requests the option in a parameter request list.
Clients using this option MUST discard DHCPOFFER or DHCPACK packets Clients using this option MUST discard DHCPOFFER or DHCPACK packets
that do not contain this option. that do not contain this option.
This option provides the DHCP server additional information upon This option provides the DHCP server additional information upon
which to make a determination of address to be assigned. The DHCP which to make a determination of address to be assigned. The DHCP
server, if it is configure to support this option, should use this server, if it is configure to support this option, should use this
information in addition to other options included in the DHCPDISCOVER information in addition to other options included in the DHCPDISCOVER
packet in order to assign an IP address for DHCP client. packet in order to assign an IP address for DHCP client.
In the event that a VPN Informmation Option and a VPN Information In the event that a VSS Informmation Option and a VSS Information
Relay Suboption are both received in a particular DHCP client packet, Relay Suboption are both received in a particular DHCP client packet,
the information from the VPN Information Suboption MUST be used in the information from the VSS Information Suboption MUST be used in
preference to the information in the VPN Information Option. preference to the information in the VSS Information Option.
Servers that do not understand this option will allocate an address Servers that do not understand this option will allocate an address
using their normal algorithms and will not return this option in the using their normal algorithms and will not return this option in the
DHCPOFFER or DHCPACK. In this case the client will discard the DHCPOFFER or DHCPACK. In this case the client will discard the
DHCPOFFER or DHCPACK. Servers that understand this option but are DHCPOFFER or DHCPACK. Servers that understand this option but are
administratively configured to ignore the option MUST ignore the administratively configured to ignore the option MUST ignore the
option, use their normal algorithms to allocate an address, and MUST option, use their normal algorithms to allocate an address, and MUST
NOT return this option in the DHCPOFFER or DHCPACK. In this case the NOT return this option in the DHCPOFFER or DHCPACK. In this case the
client will discard the DHCPOFFER or DHCPACK. In other words, this client will discard the DHCPOFFER or DHCPACK. In other words, this
option MUST NOT appear in a DHCPOFFER from a server unless it was option MUST NOT appear in a DHCPOFFER from a server unless it was
used by the server in making the address allocation requested. used by the server in making the address allocation requested.
This option SHOULD NOT be used without also making use of the DHCP This option SHOULD NOT be used without also making use of the DHCP
Authentication option [5]. Authentication option [5].
3.0 Security Considerations 3. Security Considerations
Message authentication in DHCP for intradomain use where the out-of- Message authentication in DHCP for intradomain use where the out-of-
band exchange of a shared secret is feasible is defined in [5]. band exchange of a shared secret is feasible is defined in [5].
Potential exposures to attack are discussed in section 7 of the DHCP Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification in [2]. protocol specification in [2].
The VPN Information option could be used by a client in order to The VSS Information option could be used by a client in order to
obtain an IP address from a VPN other than the one where it should. obtain an IP address from a VSS other than the one where it should.
DHCP relays MAY choose to remove the option before passing on DHCP relays MAY choose to remove the option before passing on
DHCPDISCOVER packets. Another possible defense would be for the DHCP DHCPDISCOVER packets. Another possible defense would be for the DHCP
relay to insert a Relay option containing a VPN Information relay to insert a Relay option containing a VSS Information
Suboption, which would override the DHCP VPN Information option. Suboption, which would override the DHCP VSS Information option.
This option would allow a client to perform a more complete address- This option would allow a client to perform a more complete
pool exhaustion attack since the client would no longer be restricted address-pool exhaustion attack since the client would no longer be
to attacking address-pools on just its local subnet. restricted to attacking address-pools on just its local subnet.
Servers that implement the VPN Information option MUST by default Servers that implement the VSS Information option MUST by default
disable use of the feature; it must specifically be enabled through disable use of the feature; it must specifically be enabled through
configuration. Moreover, a server SHOULD provide the ability to configuration. Moreover, a server SHOULD provide the ability to
selectively enable use of the feature under restricted conditions, selectively enable use of the feature under restricted conditions,
e.g., by enabling use of the option only from explicitly configured e.g., by enabling use of the option only from explicitly configured
client-ids, enabling its use only by clients on a particular subnet, client-ids, enabling its use only by clients on a particular subnet,
or restricting the VPNs from which addresses may be requested. or restricting the VSSs from which addresses may be requested.
4.0 IANA Considerations 4. IANA Considerations
IANA has assigned a value of TBD for the DHCP option code described No assignment of values for the type field need be made at this time.
in this document. No assignment of values for the type field need be New values may only be defined by IETF Consensus, as described in
made at this time. New values may only be defined by IETF Consensus, [6]. Basically, this means that they are defined by RFCs approved by
as described in [6]. Basically, this means that they are defined by the IESG.
RFCs approved by the IESG.
Moreover, any changes or additions to the type byte codes MUST be Moreover, any changes or additions to the type byte codes MUST be
made concurrently in the type byte codes of the VPN Information made concurrently in the type byte codes of the VSS Information
Option. The type bytes and data formats of the VPN Information Option. The type bytes and data formats of the VSS Information
Option and VPN Information Suboption MUST always be identical. Option and VSS Information Suboption MUST always be identical.
5.0 Acknowledgements 5. Acknowledgements
This document is the result of work done within Cisco Systems. This document is the result of work done within Cisco Systems.
Thanks to Kim Kinnear, Mark Stapp, and Jay Kumarasamy for their work Thanks to Kim Kinnear, Mark Stapp, and Jay Kumarasamy for their work
on this option definition and the other related work for which this on this option definition and the other related work for which this
is necessary. is necessary.
Copyright notice 6 References
Copyright (C) The Internet Society (2004). 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.
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.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Requirement Levels", RFC 2119, BCP 14, March 1997. Levels", RFC 2119, BCP 14, March 1997.
[2] Droms, R. "Dynamic Host Configuration Protocol", RFC 2131, [2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[3] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor [3] Droms, R. and S. Alexander, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. Extensions", RFC 2132, March 1997.
[4] Fox, B. and Gleeson, B., "Virtual Private Networks [4] Fox, B. and B. Gleeson, "Virtual Private Networks Identifier",
Identifier", RFC 2685, September 1999 RFC 2685, September 1999.
[5] Droms, R. "Authentication for DHCP Messages", RFC 3118, [5] Droms, R., "Authentication for DHCP Messages", RFC 3118, June
June 2001 2001.
[6] Narten, T. and Alvestrand, H., [6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
"Guidelines for Writing an IANA Considerations Section in RFCs", Considerations Section in RFCs", RFC 2434, October 1998.
RFC 2434, October 1998
Author Information: [7] Volz, B., "Reclassifying Dynamic Host Configuration Protocol
version 4 (DHCPv4) Options", RFC 3942, November 2004.
Richard Johnson Authors' Addresses
Jay Kumarasamy
Richard A. Johnson
Cisco Systems Cisco Systems
170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 San Jose, CA 95134
US
Phone: (408) 526-4000 Phone: +1 408 526 4000
EMail: raj@cisco.com
Jay Kumarasamy
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134
US
Phone: +1 408 526 4000
EMail: jayk@cisco.com EMail: jayk@cisco.com
raj@cisco.com
Kim Kinnear Kim Kinnear
Cisco Systems
250 Apollo Drive
Chelmsford, MA 01824
US
Phone: +1 978 244 8000
EMail: kkinnar@cisco.com
Mark Stapp Mark Stapp
Cisco Systems Cisco Systems
250 Apollo Drive 250 Apollo Drive
Chelmsford, MA 01824 Chelmsford, MA 01824
US
Phone: (978) 244-8000 Phone: +1 978 244 8000
EMail: mjs@cisco.com
EMail: kkinnear@cisco.com Intellectual Property Statement
mjs@cisco.com
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"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.
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