draft-ietf-dhc-fqdn-opt-02.txt		draft-ietf-dhc-fqdn-opt-03.txt
	Network Working Group Yakov Rekhter, cisco Systems		Network Working Group Yakov Rekhter, cisco Systems
	INTERNET DRAFT Ralph Droms, Bucknell University		INTERNET DRAFT Ralph Droms, Bucknell University
	Obsoletes: draft-ietf-dhc-fqdn-opt-01.txt March 1997		Obsoletes: draft-ietf-dhc-fqdn-opt-02.txt July 1997
	Expires September 1997		Expires January 1998
	An option for FQDNs in DHCP options		An option for FQDNs in DHCP options
	<draft-ietf-dhc-fqdn-opt-02.txt>		<draft-ietf-dhc-fqdn-opt-03.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft. Internet-Drafts are working		This document is an Internet-Draft. Internet-Drafts are working
	documents of the Internet Engineering Task Force (IETF), its areas,		documents of the Internet Engineering Task Force (IETF), its areas,
	and its working groups. Note that other groups may also distribute		and its working groups. Note that other groups may also distribute
	working documents as Internet-Drafts.		working documents as Internet-Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	skipping to change at page 1, line 41		skipping to change at page 1, line 41
	DHCP [DHCP] can be used to automate the process of configuring TCP/IP		DHCP [DHCP] can be used to automate the process of configuring TCP/IP
	host computers. However, some of the DHCP options carry IP addresses		host computers. However, some of the DHCP options carry IP addresses
	rather than Fully Qualified Domain Names (FQDN). Use of IP addresses		rather than Fully Qualified Domain Names (FQDN). Use of IP addresses
	constrains the DHCP client to use the addresses that were in use at		constrains the DHCP client to use the addresses that were in use at
	the time the client received its configuration information; these		the time the client received its configuration information; these
	addresses may change over time, (e.g., a server may be assigned a new		addresses may change over time, (e.g., a server may be assigned a new
	IP address), so that the IP addresses used by the client may become		IP address), so that the IP addresses used by the client may become
	invalid.		invalid.
	An alternative to passing IP addresses is to pass FQDNs instead of		An alternative to passing IP addresses is to pass FQDNs instead of
	(numeric) IP addresses. Doing this allows to defer binding between a		(numeric) IP addresses. Doing this allows a client to defer binding
	particular network entity (e.g., a server) and its IP address until		between a particular network entity (e.g., a server) and its IP
	run time. As stated in [Carpenter:96], "Deferring the binding avoids		address until run time. As stated in [Carpenter:96], "Deferring the
	the risk of changed mapping between IP addresses and specific network		binding avoids the risk of changed mapping between IP addresses and
	entities (due to changing addressing information). Moreover,		specific network entities (due to changing addressing information).
	reliance on FQDNs (rather than IP addresses) also localizes to the		Moreover, reliance on FQDNs (rather than IP addresses) also localizes
	DNS the changes needed to deal with changing addressing information		to the DNS the changes needed to deal with changing addressing
	due to renumbering."		information due to renumbering."
	DRAFT An option for FQDNs in DHCP options March 1997		DRAFT An option for FQDNs in DHCP options July 1997
	This document defines a new DHCP option that allows the use of FQDNs		This document defines a new DHCP option that allows the use of FQDNs
	instead of IP addresses in DHCP options.		instead of IP addresses in DHCP options.
	1. FQDN Option		1. FQDN Option
	The FQDN option allows the use of FQDNs rather than IP addresses in		The FQDN option allows the use of FQDNs rather than IP addresses in
	DHCP options. The FQDN option contains other DHCP options, which		DHCP options. The FQDN option contains other DHCP options, which
	then carry FQDNs rather than IP addresses as data.		then carry FQDNs rather than IP addresses as data.
	The code for the FQDN option is 89. The Len field gives the total		The code for the FQDN option is 89. The Len field gives the total
	length of all of the DHCP options contained in the FQDN option. The		length of all of the DHCP options contained in the FQDN option. The
	Code, Len, Subcode and Sublen are all one octet long. The FQDN field		Code, Len, Subcode and Sublen are all one octet long. The FQDN field
	is variable length.		is variable length.
	For each subcode carried in the FQDN option, the IP address in the		For each subcode carried in the FQDN option, the IP address in the
	option represented by the subcode is replaced by a FQDN.		option represented by the subcode is replaced by a FQDN.
	The Sublen field shall be set to the length (in octets) of the FQDN		The Sublen field shall be set to the length (in octets) of the FQDN
	carried in the option. The FQDN field carries the FQDN itself.		carried in the option; the length specified by the Sublen field does
			not include the Subcode and Sublen fields. The FQDN field carries
			the FQDN itself.
	+----------+----------+		+----------+----------+
	| Code | Len |		| Code | Len |
	+----------+----------+---------+-----------+--------------------		+----------+----------+---------+-----------+--------------------
	| Subcode | Sublen | FQDN		| Subcode | Sublen | FQDN
	+----------+----------+---------+-----------+--------------------		+----------+----------+---------+-----------+--------------------
	..................		..................
	+----------+----------+---------+-----------+--------------------		+----------+----------+---------+-----------+--------------------
	| Subcode | Sublen | FQDN		| Subcode | Sublen | FQDN
	+----------+----------+---------+-----------+--------------------		+----------+----------+---------+-----------+--------------------
	1.1 DHCP options containing a list of parameters		1.1 DHCP options containing a list of parameters
	More that one triple with a given subcode may appear within a single		More than one triple with a given subcode may appear within a single
	FQDN option. The FQDNs contained in triples with the same subcode		FQDN option. The FQDNs contained in triples with the same subcode
	should be treated as a list of parameters for the DHCP option		should be treated as a list of parameters for the DHCP option
	represented by the subcode.		represented by the subcode.
	Because FQDNs are variable length, lists of FQDNs cannot be encoded		Because FQDNs are variable length, lists of FQDNs cannot be encoded
	in DHCP options within the FQDN option. DHCP Options that can carry		in DHCP options within the FQDN option. DHCP Options that can carry
	a list of IP addresses should be coded as multiple subcodes in the		a list of IP addresses should be coded as multiple subcodes in the
	FQDN option, to differentiate among the variable-length FQDNs.
	DRAFT An option for FQDNs in DHCP options March 1997		DRAFT An option for FQDNs in DHCP options July 1997
			FQDN option, to differentiate among the variable-length FQDNs. If
			the order of the IP addresses in the option identified by the subcode
			was meaningful, e.g., representing a priority or preference order,
			the order retains that same meaning in multiple instances of the same
			subcode in the FQDN option. DHCP options that carry pairs of IP
			addresses, e.g., the static route option (code 33), MUST NOT be
			encoded in the FQDN option.
	This option only allows the use of FQDNs for options that have been		This option only allows the use of FQDNs for options that have been
	elsewhere defined to carry IP addresses.		elsewhere defined to carry IP addresses. If the FQDN option is used,
			the DNS server option (code 6) SHOULD be specified before any FQDN
			options, and the client's protocol software MUST initialize its DNS
			resolver with that DNS server address before resolving any FQDNs in
			subsequent options. Not all DHCP options that specify IP addresses
			may be sensibly transmitted as FQDNs; for example, options that
			specify an IP address-subnet mask pair MUST NOT be encoded in the
			FQDN option. The DNS server option SHOULD NOT be encoded in the FQDN
			option because, under most circumstances, the FQDN of a DNS server
			cannot be resolved until the IP address fo a server is available.
			The router option SHOULD NOT be encoded as an FQDN because queries to
			the DNS server may require that the client's protocol software be
			initialized with the router's IP address; e.g., the DNS server may be
			on a different subnet.
	1.2 Example		1.2 Example
	The following illustrates how the FQDN option could be used to carry		The following illustrates how the FQDN option could be used to carry
	FQDNs for 2 LPR Servers with FQDNs lpr1.xxx.org and lpr2.yy.org, and		FQDNs for 2 LPR Servers with FQDNs lpr1.xxx.org and lpr2.yy.org, and
	one Network Information Server with FQDN nis.zzzz.org.		one Network Information Server with FQDN nis.zzzz.org.
	+---+---+		+---+---+
	|xx |41 |		|89 |41 |
	+---+---+---+---+---+---+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
	|41 |12 | n | i | s | . | z | z | z | z | . | o | r | g |		|41 |12 | n | i | s | . | z | z | z | z | . | o | r | g |
	+---+---+---+---+---+---+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
	| 9 |12 | l | p | r | 1 | . | x | x | x | . | o | r | g |		| 9 |12 | l | p | r | 1 | . | x | x | x | . | o | r | g |
	+---+---+---+---+---+---+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
	| 9 |11 | l | p | r | 2 | . | y | y | . | o | r | g |		| 9 |11 | l | p | r | 2 | . | y | y | . | o | r | g |
	+---+---+---+---+---+---+---+---+---+---+---+---+---+		+---+---+---+---+---+---+---+---+---+---+---+---+---+
	2. Security Considerations		2. Security Considerations
	Security issues are not discussed in this document.		DHCP currently provides no authentication or security mechanisms.
			Potential exposures to attack are discussed in section 7 of the DHCP
			protocol specification [1].
			DRAFT An option for FQDNs in DHCP options July 1997
			The DHCP FQDN option introduces DNS into the client configuration
			process, so that compromises to the DNS system may compromise the
			security of client configuration.
	3. References		3. References
	[Carpenter:96] Carpenter, B., Rekhter, Y., "Renumbering needs work",		[Carpenter:96] Carpenter, B., Rekhter, Y., "Renumbering needs work",
	RFC1900, February 1996.		RFC1900, February 1996.
	[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,		[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC2131,
	October 1993.		March 1997.
	4. Acknowledgments		4. Acknowledgments
	The authors gratefully acknowledge the input and review of the		The authors gratefully acknowledge the input and review of the
	Dynamic Host Configuration working group. They also thank cisco		Dynamic Host Configuration working group. They also thank cisco
	Systems and Bucknell University for their support in the development		Systems and Bucknell University for their support in the development
	of this document.		of this document.
	DRAFT An option for FQDNs in DHCP options March 1997
	5. Author Information		5. Author Information
	Yakov Rekhter		Yakov Rekhter
	cisco Systems, Inc.		cisco Systems, Inc.
	170 Tasman Dr.		170 Tasman Dr.
	San Jose, CA 95134		San Jose, CA 95134
	Phone: (914) 528-0090		Phone: (914) 528-0090
	email: yakov@cisco.com		email: yakov@cisco.com
End of changes.
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