draft-ietf-dhc-subnet-option-05.txt		draft-ietf-dhc-subnet-option-06.txt
	Network Working Group G. Waters		Network Working Group G. Waters
	INTERNET-DRAFT Nortel Networks		INTERNET-DRAFT Nortel Networks
	June 2000		July 2000
	The Subnet Selection Option for DHCP		The IPv4 Subnet Selection Option for DHCP
	<draft-ietf-dhc-subnet-option-05.txt>		<draft-ietf-dhc-subnet-option-06.txt>
	Wednesday, June 07, 2000, 4:44 PM		Friday, July 14, 2000, 2:07 PM
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with all		This document is an Internet-Draft and is in full conformance with all
	provisions of Section 10 of RFC2026.		provisions of Section 10 of RFC2026.
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	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2000). All Rights Reserved.		Copyright (C) The Internet Society (2000). All Rights Reserved.
	Abstract		Abstract
	This memo defines a new DHCP option for selecting the subnet on which		This memo defines a new DHCP option for selecting the subnet on which
	to allocate an address. This option would override a DHCP server's		to allocate an address. This option would override a DHCP server's
	normal methods of selecting the subnet on which to allocate an address		normal methods of selecting the subnet on which to allocate an address
	for a client.		for a client.
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	Table of Contents		Table of Contents
	1. Introduction......................................................2		1. Introduction......................................................2
	1.1. Motivational Example.........................................2		1.1. Motivational Example.........................................2
	2. Subnet Selection Option Definition................................3		2. Subnet Selection Option Definition................................3
	3. Intellectual Property.............................................4		3. Intellectual Property.............................................4
	4. IANA Considerations...............................................4		4. IANA Considerations...............................................5
	5. Acknowledgements..................................................5		5. Acknowledgements..................................................5
	6. Security Considerations...........................................5		6. Security Considerations...........................................5
	7. References........................................................5		7. References........................................................5
	8. Editor's Addresses................................................5		8. Editor's Addresses................................................5
	9. Full Copyright Statement..........................................5		9. Full Copyright Statement..........................................6
	1. Introduction		1. Introduction
			The Dynamic Host Configuration Protocol (DHCP) [RFC2131] provides a
			framework for passing configuration information to hosts on a TCP/IP
			network. RFC 2132 [RFC2132] specifies DHCP option configuration
			information that may be carried in DHCP packets to/from the DHCP
			server and the DHCP client. This document specifies a new DHCP option.
	To select the subnet on which to allocate an address, the DHCP server		To select the subnet on which to allocate an address, the DHCP server
	determines the subnet from which the request originated, and then		determines the subnet from which the request originated, and then
	selects an address on the originating subnet or on a subnet that is on		selects an address on the originating subnet or on a subnet that is on
	the same network segment as the originating subnet. The subnet from		the same network segment as the originating subnet. The subnet from
	which the request originates can be determined by:		which the request originates can be determined by:
	o Using the subnet address of the giaddr field in the DHCP packet		o Using the subnet address of the giaddr field in the DHCP packet
	header, or if the giaddr field is zero;		header, or if the giaddr field is zero;
	o Using the subnet address of the local interface on which the DHCP		o Using the subnet address of the local interface on which the DHCP
	skipping to change at line 92		skipping to change at line 92
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	1.1. Motivational Example		1.1. Motivational Example
	An example of where this option could be useful is in a device (e.g.:		An example of where this option could be useful is in a device (e.g.:
	a RAS device) that is allocating addresses on behalf of its clients.		a RAS device) that is allocating addresses on behalf of its clients.
	In this case the device would be allocating addresses through DHCP and		In this case the device would be allocating addresses through DHCP and
	then managing those addresses among its clients.		then managing those addresses among its clients.
			Waters Expires: Jul 2000 + 6 months [Page 2]
	In this scenario, the device is connected to a private "internal"		In this scenario, the device is connected to a private "internal"
	network on which the DHCP server would be located. The device is also		network on which the DHCP server would be located. The device is also
	connected to one or more service providing "external" networks (i.e.:		connected to one or more service providing "external" networks (i.e.:
	the networks that the device's clients are connected to). Furthermore,		the networks that the device's clients are connected to). Furthermore,
	the internal network is not IP connected to the external networks,		the internal network is not IP connected to the external networks,
	Waters Expires: Jun 2000 + 6 months [Page 2]
	although inside the device there is connectivity between the internal		although inside the device there is connectivity between the internal
	and external networks (e.g.: though the backplane).		and external networks (e.g.: though the backplane).
	Recall that the device is allocating addresses for its clients on the		Recall that the device is allocating addresses for its clients on the
	external networks and that there is no IP connectivity between the		external networks and that there is no IP connectivity between the
	internal network and the external networks. The DHCP requests cannot		internal network and the external networks. The DHCP requests cannot
	originate from the external networks since packets cannot be routed		originate from the external networks since packets cannot be routed
	between the external network and the internal network. Thus, the DHCP		between the external network and the internal network. Thus, the DHCP
	requests must originate from the internal network. The problem with		requests must originate from the internal network. The problem with
	originating the DHCP requests from the internal network is that the		originating the DHCP requests from the internal network is that the
	skipping to change at line 123		skipping to change at line 122
	The device would send its DHCP request on the internal subnet, but		The device would send its DHCP request on the internal subnet, but
	would include the subnet selection option containing the address of		would include the subnet selection option containing the address of
	the external subnet on which it requires the address. The subnet		the external subnet on which it requires the address. The subnet
	selection option instructs the DHCP server to allocate the address on		selection option instructs the DHCP server to allocate the address on
	the requested subnet as opposed to the normal operation of allocating		the requested subnet as opposed to the normal operation of allocating
	the address on the subnet from which the DHCP request originated.		the address on the subnet from which the DHCP request originated.
	2. Subnet Selection Option Definition		2. Subnet Selection Option Definition
	The subnet selection option is a DHCP option. The option contains a		The subnet selection option is a DHCP option. The option contains a
	single IP address that is the address of a subnet. The value for the		single IPv4 address that is the address of a subnet. The value for the
	subnet address is determined by taking any IP address on the subnet		subnet address is determined by taking any IPv4 address on the subnet
	and ANDing that address with the subnet mask (i.e.: the network and		and ANDing that address with the subnet mask (i.e.: the network and
	subnet bits are left alone and the remaining (address) bits are set to		subnet bits are left alone and the remaining (address) bits are set to
	zero). When the DHCP server is allocating an address and this option		zero). When the DHCP server is configured to respond to this option,
	is present then the DHCP server MUST allocate the address on either:		is allocating an address, and this option is present then the DHCP
			server MUST allocate the address on either:
	o the subnet specified in the subnet selection option, or;		o the subnet specified in the subnet selection option, or;
	o a subnet on the same network segment as the subnet specified in the		o a subnet on the same network segment as the subnet specified in the
	subnet selection option.		subnet selection option.
	The format of the option is:		The format of the option is:
	Code Len IP Address		Code Len IPv4 Address
	+-----+-----+-----+-----+-----+-----+		+-----+-----+-----+-----+-----+-----+
	| TBD | 4 | A1 | A2 | A3 | A4 |		| TBD | 4 | A1 | A2 | A3 | A4 |
	+-----+-----+-----+-----+-----+-----+		+-----+-----+-----+-----+-----+-----+
	Servers supporting this option MUST return an identical copy of the		Waters Expires: Jul 2000 + 6 months [Page 3]
	option to any client that sends it, regardless of whether or not the		Servers configured to support this option MUST return an identical
	client requests the option in a parameter request list. Clients using		copy of the option to any client that sends it, regardless of whether
	this option MUST discard DHCPOFFER or DHCPACK packets that do not		or not the client requests the option in a parameter request list.
	contain this option.		Clients using this option MUST discard DHCPOFFER or DHCPACK packets
			that do not contain this option.
	Waters Expires: Jun 2000 + 6 months [Page 3]
	This option does not require changes to operations or features of the		This option does not require changes to operations or features of the
	DHCP server other than to select the subnet on which to allocate an		DHCP server other than to select the subnet on which to allocate an
	address. For example, the handling of DHCPDISCOVER for an unknown		address. For example, the handling of DHCPDISCOVER for an unknown
	subnet should continue to operate unchanged.		subnet should continue to operate unchanged.
	When this option is present and the server supports this option, the		When this option is present and the server is configured to support
	server MUST NOT offer an address that is not on the requested subnet		this option, the server MUST NOT offer an address that is not on the
	or network segment.		requested subnet or network segment. Servers that do not understand
			this option will allocate an address 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. Servers that
			understand this option but are administratively configured to ignore
			the option MUST ignore the option, use their normal algorithms to
			allocate an address, and MUST NOT return this option in the DHCPOFFER
			or DHCPACK. In this case the client will discard the DHCPOFFER or
			DHCPACK.
	During an address renew, the DHCP server may send a DHCPACK directly		During an address renew, the DHCP server may send a DHCPACK directly
	to the allocated address, however packets from the DHCP server may not		to the allocated address, however packets from the DHCP server may not
	be routable to the address. Thus, in all packets that the DHCP client		be routable to the address. Thus, in all packets that the DHCP client
	sends that contain the subnet selection option, the giaddr field in		sends that contain the subnet selection option, the giaddr field in
	the BOOTP header MUST be set to an IP address on which the DHCP client		the BOOTP header MUST be set to an IPv4 address on which the DHCP
	will accept DHCP packets (e.g.: the address of the subnet connected to		client will accept DHCP packets (e.g.: the address on the subnet
	the internal network).		connected to the internal network).
	The IP address to which a DHCP server sends a reply to MUST be the		The IPv4 address to which a DHCP server sends a reply to MUST be the
	same as it would chose when this option is not present.		same as it would chose when this option is not present.
	3. Intellectual Property		3. Intellectual Property
	The IETF takes no position regarding the validity or scope of any		The IETF takes no position regarding the validity or scope of any
	intellectual property or other rights that might be claimed to pertain		intellectual property or other rights that might be claimed to pertain
	to the implementation or use of the technology described in this		to the implementation or use of the technology described in this
	document or the extent to which any license under such rights might or		document or the extent to which any license under such rights might or
	might not be available; neither does it represent that it has made any		might not be available; neither does it represent that it has made any
	effort to identify any such rights. Information on the IETF's		effort to identify any such rights. Information on the IETF's
	procedures with respect to rights in standards-track and standards-		procedures with respect to rights in standards-track and standards-
	related documentation can be found in BCP-11.		related documentation can be found in BCP-11.
	Copies of claims of rights made available for publication and any		Copies of claims of rights made available for publication and any
	assurances of licenses to be made available, or the result of an		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		attempt made to obtain a general license or permission for the use of
	such proprietary rights by implementers or users of this specification		such proprietary rights by implementers or users of this specification
	can be obtained from the IETF Secretariat.		can be obtained from the IETF Secretariat.
			Waters Expires: Jul 2000 + 6 months [Page 4]
	The IETF invites any interested party to bring to its attention any		The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary		copyrights, patents or patent applications, or other proprietary
	rights which may cover technology that may be required to practice		rights which may cover technology that may be required to practice
	this standard. Please address the information to the IETF Executive		this standard. Please address the information to the IETF Executive
	Director.		Director.
	4. IANA Considerations		4. IANA Considerations
	IANA has assigned a value of TBD for the DHCP option code described in		IANA has assigned a value of TBD for the DHCP option code described in
	this document.		this document.
	Waters Expires: Jun 2000 + 6 months [Page 4]
	5. Acknowledgements		5. Acknowledgements
	This document is the result of work undertaken the by DHCP working		This document is the result of work undertaken the by DHCP working
	group. Thanks to Ted Lemon, Tim Aston and Ralph Droms for their		group. Thanks to Ted Lemon, Tim Aston and Ralph Droms for their
	helpful comments in this work.		helpful comments in this work.
	6. Security Considerations		6. Security Considerations
	DHCP currently provides no authentication or security mechanisms.		DHCP currently provides no authentication or security mechanisms.
	Potential exposures to attack are discussed is section 7 of the		Potential exposures to attack are discussed is section 7 of the
	skipping to change at line 233		skipping to change at line 241
	March 1997.		March 1997.
	[RFC2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor		[RFC2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor
	Extensions", RFC 2132, March 1997.		Extensions", RFC 2132, March 1997.
	8. Editor's Addresses		8. Editor's Addresses
	Glenn Waters		Glenn Waters
	Nortel Networks		Nortel Networks
	310-875 Carling Avenue,		310-875 Carling Avenue,
			Waters Expires: Jul 2000 + 6 months [Page 5]
	Ottawa, Ontario K1S 5P1		Ottawa, Ontario K1S 5P1
	Canada		Canada
	Phone: +1 613-798-4925		Phone: +1 613-798-4925
	Email: gww@nortelnetworks.com		Email: gww@nortelnetworks.com
	9. Full Copyright Statement		9. Full Copyright Statement
	Copyright (C) The Internet Society (2000). All Rights Reserved.		Copyright (C) The Internet Society (2000). All Rights Reserved.
	This document and translations of it may be copied and furnished to		This document and translations of it may be copied and furnished to
	others, and derivative works that comment on or otherwise explain it		others, and derivative works that comment on or otherwise explain it
	or assist in its implementation may be prepared, copied, published and		or assist in its implementation may be prepared, copied, published and
	Waters Expires: Jun 2000 + 6 months [Page 5]
	distributed, in whole or in part, without restriction of any kind,		distributed, in whole or in part, without restriction of any kind,
	provided that the above copyright notice and this paragraph are		provided that the above copyright notice and this paragraph are
	included on all such copies and derivative works. However, this		included on all such copies and derivative works. However, this
	document itself may not be modified in any way, such as by removing		document itself may not be modified in any way, such as by removing
	the copyright notice or references to the Internet Society or other		the copyright notice or references to the Internet Society or other
	Internet organizations, except as needed for the purpose of developing		Internet organizations, except as needed for the purpose of developing
	Internet standards in which case the procedures for copyrights defined		Internet standards in which case the procedures for copyrights defined
	in the Internet Standards process must be followed, or as required to		in the Internet Standards process must be followed, or as required to
	translate it into languages other than English.		translate it into languages other than English.
	The limited permissions granted above are perpetual and will not be		The limited permissions granted above are perpetual and will not be
	revoked by the Internet Society or its successors or assigns.		revoked by the Internet Society or its successors or assigns.
	This document and the information contained herein is provided on an		This document and the information contained herein is provided on an
	"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING		"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
	TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT		TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
	NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN		NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
	WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF		WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
	MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.		MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Waters Expires: Jun 2000 + 6 months [Page 6]		Waters Expires: Jul 2000 + 6 months [Page 6]
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