draft-ietf-dhc-dhcp-dns-09.txt		draft-ietf-dhc-dhcp-dns-10.txt
	Network Working Group Yakov Rekhter		Network Working Group Yakov Rekhter
	INTERNET-DRAFT Mark Stapp		INTERNET-DRAFT Mark Stapp
	Cisco Systems		Cisco Systems
	February 1999		June 1999
	Expires August 1999		Expires
			December 1999
	Interaction between DHCP and DNS		Interaction between DHCP and DNS
	<draft-ietf-dhc-dhcp-dns-09.txt>		<draft-ietf-dhc-dhcp-dns-10.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with		This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.		all provisions of Section 10 of RFC2026.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	other groups may also distribute working documents as Internet-		other groups may also distribute working documents as Internet-
	Drafts.		Drafts.
	skipping to change at page 1, line 40		skipping to change at page 1, line 40
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (1999). All Rights Reserved.		Copyright (C) The Internet Society (1999). All Rights Reserved.
	Abstract		Abstract
	DHCP provides a powerful mechanism for IP host autoconfiguration.		DHCP provides a powerful mechanism for IP host configuration.
	However, the autoconfiguration provided by DHCP does not include		However, the configuration capability provided by DHCP does not
	updating DNS, and specifically updating the name to address and		include updating DNS, and specifically updating the name to address
	address to name mappings maintained by DNS.		and address to name mappings maintained in the DNS.
	This document specifies how DHCP clients and servers should use the		This document specifies how DHCP clients and servers should use the
	Dynamic DNS Updates mechanism to update the DNS name to address and		Dynamic DNS Updates mechanism in [RFC2136] to update the DNS name to
	address to name mapping, so that the mappings for DHCP clients would		address and address to name mappings so that the mappings for DHCP
	be consistent with the IP addresses that the clients acquire via		clients will be consistent with the IP addresses that the clients
	DHCP.		acquire via DHCP.
	1. Terminology		1. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"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 RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	2. Interaction between DHCP and DNS		2. Interaction between DHCP and DNS
	DNS [RFC1034, RFC1035] maintains (among other things) the information		DNS [RFC1034, RFC1035] maintains (among other things) the information
	about mapping between hosts' Fully Qualified Domain Names (FQDNs)		about mapping between hosts' Fully Qualified Domain Names (FQDNs)
	[RFC1594] and IP addresses assigned to the hosts. The information is		[RFC1594] and IP addresses assigned to the hosts. The information is
	maintained in two types of Resource Records (RRs): A and PTR. The A		maintained in two types of Resource Records (RRs): A and PTR. The A
	RR contains mapping from a FQDN to an IP address; the PTR RR contains		RR contains a mapping from an FQDN to an IP address; the PTR RR con-
	mapping from an IP address to a FQDN.		tains a mapping from an IP address to a FQDN. The Dynamic DNS
			Updates specification [RFC2136] describes a mechanism that enables
			DNS information to be updated over a network.
	DHCP [RFC1541] provides a mechanism by which a host (a DHCP client)		DHCP [RFC2131] provides a mechanism by which a host (a DHCP client)
	could acquire certain configuration information, and specifically its		could acquire certain configuration information, and specifically its
	IP address(es). However, DHCP does not provide any mechanisms to		IP address(es). However, DHCP does not provide any mechanisms to
	update the DNS RRs that contain the information about mapping between		update the DNS RRs that contain the information about mapping between
	the host's FQDN and its IP address(es) (A and PTR RRs). Thus the		the host's FQDN and its IP address(es) (A and PTR RRs). Thus the
	information maintained by DNS for a DHCP client may be incorrect - a		information maintained by DNS for a DHCP client may be incorrect - a
	host (the client) could acquire its address by using DHCP, but the A		host (the client) could acquire its address by using DHCP, but the A
	RR for the host's FQDN wouldn't reflect the address that the host		RR for the host's FQDN wouldn't reflect the address that the host
	acquired, and the PTR RR for the acquired address wouldn't reflect		acquired, and the PTR RR for the acquired address wouldn't reflect
	the host's FQDN.		the host's FQDN.
	Dynamic DNS Updates [RFC2136] is a mechanism that enables DNS infor-
	mation to be updated over a network.
	The Dynamic DNS Update protocol can be used to maintain consistency		The Dynamic DNS Update protocol can be used to maintain consistency
	between the information stored in the A and PTR RRs and the actual		between the information stored in the A and PTR RRs and the actual
	address assignment done via DHCP. When a host with a particular FQDN		address assignment done via DHCP. When a host with a particular FQDN
	acquires its IP address via DHCP, the A RR associated with the host's		acquires its IP address via DHCP, the A RR associated with the host's
	FQDN would be updated (by using the Dynamic DNS Updates protocol) to		FQDN would be updated (by using the Dynamic DNS Updates protocol) to
	reflect the new address. Likewise, when an IP address gets assigned		reflect the new address. Likewise, when an IP address gets assigned
	to a host with a particular FQDN, the PTR RR associated with this		to a host with a particular FQDN, the PTR RR associated with this
	address would be updated (using the Dynamic DNS Updates protocol) to		address would be updated (using the Dynamic DNS Updates protocol) to
	reflect the new FQDN.		reflect the new FQDN.
			Although this document refers to the A and PTR DNS record types and
			to DHCP assignment of IPv4 addresses, the same procedures and
			requirements should apply for updates to the analogous RR types that
			are used when clients are assigned IPv6 addresses via DHCPv6.
	3. Models of operation		3. Models of operation
	When a DHCP client acquires a new address, both the A RR (for the		When a DHCP client acquires a new address, both the A RR (for the
	client's FQDN) and the PTR RR (for the acquired address) have to be		client's FQDN) and the PTR RR (for the acquired address) have to be
	updated. Therefore, we have two separate Dynamic DNS Update transac-		updated. Therefore, two separate Dynamic DNS Update transactions
	tions. Acquiring an address via DHCP involves two entities: a DHCP		occur. Acquiring an address via DHCP involves two entities: a DHCP
	client and a DHCP server. In principle each of these entities could		client and a DHCP server. In principle each of these entities could
	perform none, one, or both of the transactions. However, upon some		perform none, one, or both of the transactions. However, upon reflec-
	reflection one could realize that not all permutations make sense.		tion one could realize that not all permutations make sense. This
	This document covers the possible design permutations:		document covers the possible design permutations:
	(1) DHCP client updates the A RR, DHCP server updates the PTR RR		(1) DHCP client updates the A RR, DHCP server updates the PTR RR
	(2) DHCP server updates both the A and the PTR RRs		(2) DHCP server updates both the A and the PTR RRs
	One could observe that the only difference between these two cases is		One could observe that the only difference between these two cases is
	whether the FQDN to IP address mapping is updated by a DHCP client or		whether the FQDN to IP address mapping is updated by a DHCP client or
	by a DHCP server. The IP address to FQDN mapping is updated by a DHCP		by a DHCP server. The IP address to FQDN mapping is updated by a DHCP
	server in both cases.		server in both cases.
	The reason these two are important, while others are unlikely, has to		The reason these two are important, while others are unlikely, has to
	do with authority over the respective DNS RRs. A client may be given		do with authority over the respective DNS domain names. A client may
	authority over mapping its own A RRs, or that may be restricted to a		be given authority over mapping its own A RRs, or that authority may
	server to prevent the client from listing arbitrary addresses. In		be restricted to a server to prevent the client from listing arbi-
	all cases, the only reasonable place for the authority over the PTR		trary addresses or associating its address with arbitrary domain
	RRs associated with the address is in the DHCP server that allocates		names. In all cases, the only reasonable place for the authority over
	them.		the PTR RRs associated with the address is in the DHCP server that
			allocates them.
			In any case, whether a site permits all, some, or no DHCP servers and
			clients to perform DNS updates into the zones which it controls is
			entirely a matter of local administrative policy. This document does
			not require any specific administrative policy, and does not propose
			one. The range of possible policies is very broad, from sites where
			only the DHCP servers have been given credentials that the DNS
			servers will accept, to sites where each individual DHCP client has
			been configured with credentials which allow the client to modify its
			own domain name. Compliant implementations will support some or all
			of these possibilities.
			This document describes a new DHCP option which a client can use to
			convey all or part of its domain name to a DHCP server. Site-specific
			policy determines whether DHCP servers use the names that clients
			offer or not, and what DHCP servers should do in cases where clients
			do not supply domain names.
	3.1. Client FQDN Option		3.1. Client FQDN Option
	To update the IP address to FQDN mapping a DHCP server needs to know		To update the IP address to FQDN mapping a DHCP server needs to know
	FQDN of the client to which the server leases the address. To allow		the FQDN of the client to which the server leases the address. To
	the client to convey its FQDN to the server this document defines a		allow the client to convey its FQDN to the server this document
	new option, called "Client FQDN".		defines a new DHCP option, called "Client FQDN". The FQDN Option also
			contains Flags and RCode fields which DHCP servers can use to convey
			information about DNS updates to clients.
			Clients MAY send the FQDN option, setting appropriate Flags values,
			in both their DISCOVER and REQUEST messages. If a client sends the
			FQDN option in its DISCOVER message, it MUST send the option in sub-
			sequent REQUEST messages.
	The code for this option is 81. Its minimum length is 4.		The code for this option is 81. Its minimum length is 4.
	Code Len Flags RCODE1 RCODE2 Domain Name		Code Len Flags RCODE1 RCODE2 Domain Name
	+------+------+------+------+------+------+--		+------+------+------+------+------+------+--
	| 81 | n | | | | ...		| 81 | n | | | | ...
	+------+------+------+------+------+------+--		+------+------+------+------+------+------+--
	The Flags field allows a DHCP client to indicate to a DHCP server		3.1.1. The Flags Field
	whether (a) the client wants to be responsible for updating the FQDN
	to IP address mapping (if Flags is set to 0), or (b) the client wants		This figure presents the format of the Flags field, which is one byte
	the server to be responsible for updating the FQDN to IP address map-		long:
	ping (if Flags is set to 1). The Flags field also allows a DHCP
	server to indicate to a DHCP client that the server assumes the		0 1 2 3 4 5 6 7
	responsibility for updating the FQDN to IP address mapping, even if		+-+-+-+-+-+-+-+-+
	the client wants to be responsible for this update (if Flags is set		| MBZ |E|O|S|
	to 3).		+-+-+-+-+-+-+-+-+
			When a client sends the FQDN option in its DHCPDISCOVER and/or
			DHCPREQUEST messages, it sets the right-most bit (labelled "S") to
			indicate that it will not perform any Dynamic DNS updates, and that
			it expects the DHCP server to perform any FQDN-to-IP (the A RR) DNS
			update on its behalf. If this bit is clear, the client indicates that
			it intends to perform its own FQDN-to-IP mapping update.
			If a DHCP server intends to take responsibility for the A RR update
			whether or not the client sending the FQDN option has set the "S"
			bit, it sets both the "O" bit and the "S" bit, and sends the FQDN
			option in its corresponding DHCPOFFER and/or DHCPACK messages.
			The data in the Domain Name field may appear in one of two formats:
			ASCII, or DNS-style binary encoding (without compression, of course).
			A client which sends the FQDN option sets the "E" bit to indicate
			that the data in the Domain Name field is DNS-encoded, as described
			in [RFC1035].
			The remaining bits in the Flags field are reserved for future assign-
			ment. DHCP clients and servers which send the FQDN option MUST set
			the MBZ bits to 0, and they MUST ignore values in the part of the
			field labelled "MBZ".
			3.1.2. The RCODE Fields
	The RCODE1 and RCODE2 fields are used by a DHCP server to indicate to		The RCODE1 and RCODE2 fields are used by a DHCP server to indicate to
	a DHCP client the Response Code from Dynamic DNS Updates.		a DHCP client the Response Code from the an A RR Dynamic DNS Update
			performed on the client's behalf. The server also uses these fields
			to indicate whether it has attempted such an update before sending
			the DHCPACK message. Each of these fields is one byte long.
	The Domain Name part of the option carries FQDN of a client.		3.1.3. The Domain Name Field
			The Domain Name part of the option carries the FQDN of a DHCP client.
			A client may be configured with a fully-qualified domain name, or
			with a partial name that is not fully-qualified. If a client knows
			only part of its name, it MAY send a single label, indicating that it
			knows part of the name but does not necessarily know the zone in
			which the name is to be embedded. The data in the Domain Name field
			may appear in one of two formats: ASCII (with no terminating NULL),
			or DNS encoding as specified in [RFC1035]. If the DHCP client wishes
			to use DNS encoding, it MUST set the third-from-rightmost bit in the
			Flags field (the "E" bit); if it uses ASCII encoding, it must clear
			that Flags bit.
			A DHCP client that can only send a single label using ASCII encoding
			includes a series of ASCII characters in the Domain Name field,
			excluding the "." (dot) character. The client SHOULD follow the
			character-set recommendations of [RFC1034] and [RFC1035]. A client
			using DNS encoding sends a single label as a single byte count, fol-
			lowed by that number of bytes of data, without a terminal reference
			to the root.
	3.2. DHCP Client behavior		3.2. DHCP Client behavior
	The following describes behavior of a DHCP client that implements the		The following describes the behavior of a DHCP client that implements
	Client FQDN option.		the Client FQDN option.
	If a client that owns/maintains is own FQDN wants to be responsible		If a client that owns/maintains its own FQDN wants to be responsible
	for updating the FQDN to IP address mapping for the FQDN and		for updating the FQDN to IP address mapping for the FQDN and
	address(es) used by the client, then the client MUST include the		address(es) used by the client, then the client MUST include the
	Client FQDN option in the DHCPREQUEST message originated by the		Client FQDN option in the DHCPREQUEST message originated by the
	client. The Flags field in the option MUST be set to 0. Once the		client. A DHCP client MAY choose to include the Client FQDN option in
			its DISCOVER messages as well as its REQUEST messages. The rightmost
			bit in the Flags field in the option MUST be set to 0. Once the
	client's DHCP configuration is completed (the client receives a		client's DHCP configuration is completed (the client receives a
	DHCPACK message, and successfully completed a final check on the		DHCPACK message, and successfully completes a final check on the
	parameters passed in the message), the client MUST originate an		parameters passed in the message), the client SHOULD originate an
	update for the A RR (associated with the client's FQDN). The update		update for the A RR (associated with the client's FQDN). The update
	MUST be originated following the procedures described in [RFC2136].		MUST be originated following the procedures described in section 3.4.
			If the DHCP server from which the client is requesting a lease
			includes the FQDN option in its ACK message, and if the server sets
			both the "S" and the "O" bits in the option's Flags field, the client
			MUST NOT initiate an update for the name in the Domain Name field.
	A client that owns/maintains its own FQDN can choose to delegate the		A client can choose to delegate the responsibility for updating the
	responsibility for updating the FQDN to IP address mapping for the		FQDN to IP address mapping for the FQDN and address(es) used by the
	FQDN and address(es) used by the client to the server. In order to		client to the server. In order to inform the server of this choice,
	inform the server of this choice, the client MUST include the Client		the client SHOULD include the Client FQDN option in its DHCPREQUEST
	FQDN option in the DHCPREQUEST message originated by the client. The		message. The rightmost (or "S") bit in the Flags field in the option
	Flags field in the option MUST be set to 1. In this case, the client		MUST be set to 1. A client which delegates this responsibility MUST
	MAY supply an FQDN in the Client FQDN option, or it MAY leave that		NOT attempt to perform a Dynamic DNS update for the name in the
	field empty as a signal to the server to generate an FQDN for the		Domain Name field of the FQDN option. The client MAY supply an FQDN
	client in any manner the server chooses.		in the Client FQDN option, or it MAY supply a single label (the
			most-specific label), or it MAY leave that field empty as a signal to
			the server to generate an FQDN for the client in any manner the
			server chooses.
	A client that delegates the responsibility for updating the FQDN to		Since there is a possibility that the DHCP server may be configured
	IP address mapping to a server MAY not receive any indications		to complete or replace a domain name that the client was configured
	(either positive or negative) from the server whether the server was		to send, the client might find it useful to send the FQDN option in
	able to perform the update. In this case the client MAY use a DNS		its DISCOVER messages. If the DHCP server returns different Domain
	query to check whether the mapping is updated.		Name data in its OFFER message, the client could use that data in
			performing its own eventual A RR update, or in forming the FQDN
			option that it sends in its REQUEST message. There is no requirement
			that the client send identical FQDN option data in its DISCOVER and
			REQUEST messages. In particular, if a client has sent the FQDN option
			to its server, and the configuration of the client changes so that
			its notion of its domain name changes, it should send the new data in
			an FQDN option when it communicates with the server again. This may
			allow the DHCP server to update the name associated with the PTR
			record, and, if the server updated the A record representing the
			client, to delete that record and attempt an update for the client's
			current domain name.
			A client which delegates the responsibility for updating the FQDN to
			IP address mapping to a server might not receive any indication
			(either positive or negative) about the status of the update from the
			server. The client MAY use a DNS query to check whether the mapping
			is updated.
	A client MUST set the RCODE1 and RCODE2 fields in the Client FQDN		A client MUST set the RCODE1 and RCODE2 fields in the Client FQDN
	option to 0 when sending the option.		option to 0 when sending the option.
	If a client releases its address lease prior to the lease expiration		If a client releases its lease prior to the lease expiration time and
	time and the client is responsible for updating its A RR(s), the		the client is responsible for updating its A RR(s), the client SHOULD
	client SHOULD delete the A RR (following the procedures described in		delete the A RR (following the procedures described in [RFC2136])
	[RFC2136]) associated with the leased address before sending a DHCP		associated with the leased address before sending a DHCPRELEASE mes-
	RELEASE message.		sage. Similarly, if a client was responsible for updating its A RR,
			but is unable to renew its lease, the client SHOULD attempt to delete
			the A RR before its lease expires. A client which has not been able
			to delete an A RR which it added (because it has lost its IP address)
			SHOULD add an entry to its logfile and/or notify its administrator.
	3.3. DHCP Server behavior		3.3. DHCP Server behavior
	When a server receives a DHCPREQUEST message from a client, if the		When a server receives a DHCPREQUEST message from a client, if the
	message contains the Client FQDN option, and the server replies to		message contains the Client FQDN option, and the server replies to
	the message with a DHCPACK message, the server SHOULD originate an		the message with a DHCPACK message, the server SHOULD originate an
	update for the PTR RR (associated with the address leased to the		update for the PTR RR associated with the address leased to the
	client). The update MUST be originated following the procedures		client if the server is configured to perform DNS updates. The update
	described in Section 3.4. The server MAY complete the update before		MUST be originated following the procedures described in Section 3.4.
	the server sends the DHCPACK message to the client. In this case the		The server MAY complete the update before the server sends the
	RCODE from the update [RFC2136] MUST be carried to the client in the		DHCPACK message to the client. In this case the RCODE from the update
	RCODE1 field of the Client FQDN option in the DHCPACK message and the		[RFC2136] MUST be carried to the client in the RCODE1 field of the
	RCODE2 field MUST be set to 0. Alternatively, the server MAY send the		Client FQDN option in the DHCPACK message. Alternatively, the server
	DHCPACK message to the client without waiting for the update to be		MAY send the DHCPACK message to the client without waiting for the
	completed. In this case the RCODE1 field of the Client FQDN option		update to be completed. In this case the RCODE1 field of the Client
	in the DHCPACK message MUST be set to 255, and the RCODE2 field MUST		FQDN option in the DHCPACK message MUST be set to 255. The choice
	be set to 0. The choice between the two alternatives is entirely up		between the two alternatives is entirely determined by the configura-
	to the DHCP server.		tion of the DHCP server. Servers SHOULD support both configuration
			options.
	In addition, if the Client FQDN option carried in the DHCPREQUEST		In addition, if the Client FQDN option carried in the DHCPREQUEST
	message has its Flags field set to 1, then the server MUST originate		message has the "S" bit in its Flags field set, then the server MAY
	an update for the A RR (associated with the FQDN carried in the		originate an update for the A RR (associated with the FQDN carried in
	option). The update MUST be originated following the procedures		the option) if it is configured to do so by the site's administrator,
	described in Section 3.4. The server MAY originate the update before		and if it has the necessary credentials. The server MAY be configured
	the server sends the DHCPACK message to the client. In this case the		to use the name supplied by the client, or it MAY be configured to
	RCODE from the update [RFC2136] MUST be carried to the client in the		modify the supplied name, or substitute a different name.
	RCODE2 field of the Client FQDN option in the DHCPACK message.
	Alternatively the server MAY send the DHCPACK message to the client		The update MUST be originated following the procedures described in
	without waiting for the update to be completed. In this case the		Section 3.4. The server MAY originate the update before the server
	RCODE2 field of the Client FQDN option in the DHCKACK message MUST be		sends the DHCPACK message to the client. In this case the RCODE from
	set to 255. The choice between the two alternatives is entirely up to		the update [RFC2136] MUST be carried to the client in the RCODE2
	the DHCP server.		field of the Client FQDN option in the DHCPACK message. Alterna-
			tively the server MAY send the DHCPACK message to the client without
			waiting for the update to be completed. In this case the RCODE2 field
			of the Client FQDN option in the DHCPACK message MUST be set to 255.
			The choice between the two alternatives is entirely up to the DHCP
			server. In either case, if the server intends to perform the DNS
			update and the client's REQUEST message included the FQDN option, the
			server SHOULD include the FQDN option in its ACK message, and MUST
			set the "S" bit in the option's Flags field.
	Even if the Client FQDN option carried in the DHCPREQUEST message has		Even if the Client FQDN option carried in the DHCPREQUEST message has
	its Flags field set to 0 (indicating that the client wants to update		the "S" bit its Flags field clear (indicating that the client wants
	the A RR), the server MAY (at the determination of the local adminis-		to update the A RR), the server MAY, be configured byt the local
	trator) update the A RR. The update MUST be originated following the		administrator to update the A RR on the client's behalf. A server
	procedures described in Section 3.4. The server MAY originate the		which is configured to override the client's preference SHOULD
	update before the server sends the DHCPACK message to the client. In		include an FQDN option in its ACK message, and MUST set both the "O"
	this case the RCODE from the update [RFC2136] MUST be carried to the		and "S" bits in the FQDN option's Flags field. The update MUST be
	client in the RCODE2 field of the Client FQDN option in the DHCPACK		originated following the procedures described in Section 3.4. The
	message, and the Flags field in the Client FQND option MUST be set to		server MAY originate the update before the server sends the DHCPACK
	3. Alternatively, the server MAY send the DHCPACK message to the		message to the client. In this case the RCODE from the update
	client without waiting for the update to be completed. In this case		[RFC2136] MUST be carried to the client in the RCODE2 field of the
	the RCODE2 field of the Client FQDN option in the DHCKACK message		Client FQDN option in the DHCPACK message. Alternatively, the server
	MUST be set to 255, and the Flags field in the Client FQDN option		MAY send the DHCPACK message to the client without waiting for the
	MUST be set to 3. Whether the DNS update occurs before or after the		update to be completed. In this case the RCODE2 field of the Client
	DHCPACK is sent is entirely up to the DHCP server.		FQDN option in the DHCPACK message MUST be set to 255. Whether the
			DNS update occurs before or after the DHCPACK is sent is entirely up
			to the DHCP server's configuration.
	When a server receives a DHCPREQUEST message from a client, and the		When a server receives a DHCPREQUEST message from a client, and the
	message contains the Client FQDN option, the server MUST ignore the		message contains the Client FQDN option, the server MUST ignore the
	value carried in the RCODE1 and RCODE2 fields of the option.		values carried in the RCODE1 and RCODE2 fields of the option.
	When a DHCP server sends the Client FQDN option to a client in the		When a DHCP server sends the Client FQDN option to a client in the
	DHCPACK message, the server MUST copy the Domain Name fields from the		DHCPACK message, the server MUST copy the Domain Name field from the
	Client FQDN option that the client sent to the server in the DHCPRE-		Client FQDN option that the client sent to the server in the DHCPRE-
	QUEST message.		QUEST message. If, however, the client sent only a single label, or
			if the DHCP server has been configured to assign the client a name
			different from the one the client has sent, the server SHOULD send
			its notion of the complete FQDN for the client. The server MUST use
			the same encoding format (ASCII or DNS-encoding) that the client used
			in the FQDN option in its DHCPREQUEST, and MUST set the "E" bit in
			the option's Flags field accordingly.
	If the DHCPREQUST message received by a DHCP server from a DHCP		If the DHCPREQUEST message received by a DHCP server from a DHCP
	client doesn't carry the Client FQDN option (e.g., the client doesn't		client doesn't carry the Client FQDN option (e.g., the client doesn't
	implement the Client FQDN option), and the DHCP client acquires its		implement the Client FQDN option), and the DHCP client acquires its
	FQDN from a DHCP server (as part of a normal DHCP transaction), then		FQDN from a DHCP server (as part of a normal DHCP transaction), then
	the server MAY be configured to update both A and PTR RRs. The		the server MAY be configured to update both A and PTR RRs. Any
	updates MUST be originated following the procedures described in Sec-		updates MUST be originated following the procedures described in Sec-
	tion 3.4.		tion 3.4. In this case, the server MAY NOT wish to return the FQDN
			option to a client which may not be able to understand it. If it can,
			the DHCP server MAY (optionally) return the host part of the domain
			name that it will use for the client in the host-name DHCP option
			(defined in [RFC2132]). Note that it may not be possible to con-
			sistently encode some domain name data in the format specified by the
			host-name option.
	If a server detects that a lease on an address that the server leases		If a server detects that a lease on an address that the server leases
	to a client expires, the server SHOULD delete the PTR RR associated		to a client has expired or has been released by the client, the
	with the address. In addition, if the A RR (of the client) was ini-		server SHOULD delete the PTR RR which it associated with the address
	tially updated by the server, the server SHOULD also delete the A RR.		via DNS Dynamic Update. In addition, if the server added an A RR on
	The deletion MUST follow the procedures described in [RFC2136].		behalf of the client, the server SHOULD also delete the A RR. The
			deletion MUST follow the procedures described in Section 3.4.
	If a server terminates a lease on an address prior to the lease		If a server terminates a lease on an address prior to the lease's
	expiration time, the server SHOULD delete the PTR RR associated with		expiration time, for instance by sending a DHCPNAK to a client, the
	the address. In addition, if the server (that leased the address)		server SHOULD delete the PTR RR which it associated with the address
	initially updated the A RR (of the client), the server SHOULD also		via DNS Dynamic Update. In addition, if the server took responsibil-
	delete the A RR. The deletion MUST follow the procedures described in		ity for the client's A RR , the server SHOULD also delete that A RR.
	[RFC2136].		The deletion MUST follow the procedures described in Section 3.4.
	3.4. Procedures for performing DNS updates		3.4. Procedures for performing DNS updates
	There are two principal issues that need to be addressed concerning A		There are two principal issues that need to be addressed concerning A
	RR DNS updates:		RR DNS updates:
	o Name Collisions		o Name Collisions
	If the entity updating the A RR (either the DHCP client or DHCP		If the entity updating the A RR (either the DHCP client or DHCP
	server) attempts to perform a DNS update with a DNS name that is		server) attempts to perform a DNS update to a domain name that
	already in use, what should be done? In some scenarios these		has an A RR which is already in use by a different DHCP client,
	name collisions are unlikely, in some scenarios they are very		what should be done? Similarly, should a DHCP client or server
	likely:		update a domain name which has an A RR that has been configured
			by an administrator? In either of these cases, the domain name
			in question would either have an additional A RR, or would have
			its original A RR replaced by the new record. Either of these
			effects may be considered undesirable in some sites. This
			specification describes behavior designed to prevent these
			undesirable effects, and requires that implementations make this
			behavior the default. In some scenarios these name collisions
			are unlikely, in some scenarios they are very likely:
	1. Client updates A RR, uses DNSSEC: Name collisions in		1. Client updates A RR, uses DNSSEC: Name collisions in this
	this scenario are unlikely (though not impossible), since		scenario are unlikely (though not impossible), since for the
	for the client to use DNSSEC, it has already received		client to use DNSSEC, it has already received credentials
	credentials specific to the name it will add. This implies		specific to the name it desires to use. This implies that
	that the name has already been allocated (through some		the name has already been allocated (through some
	implementation- or organization-specific procedure, and		implementation- or organization-specific procedure, and
	presumably uniquely) to that client.		presumably uniquely) to that client.
	2. Client updates A RR, uses some form of TSIG: Name		2. Client updates A RR, uses some form of TSIG: Name colli-
	collisions in this scenario are possible, since the		sions in this scenario are possible, since the credentials
	credentials necessary for the client to update DNS are not		necessary for the client to update DNS are not necessarily
	name specific. Thus, for the client to be attempting to		name-specific. Thus, for the client to be attempting to
	update a unique name requires the existence of some		update a unique name requires the existence of some adminis-
	administrative procedure to ensure client configuration		trative procedure to ensure client configuration with unique
	with unique names.		names.
	3. Server updates the A RR, uses a name for the client		3. Server updates the A RR, uses a name for the client which
	which is known to the server: Name collisions in this		is known to the server: Name collisions in this scenario are
	scenario are likely unless prevented by the server' name		likely unless prevented by the server's name configuration
	configuration procedures. See Section 7 for security issues		procedures. See Section 5 for security issues with this form
	with this form of deployment.		of deployment.
	4. Server updates the A RR, uses a name supplied by the		4. Server updates the A RR, uses a name supplied by the
	client: Name collisions in this scenario are highly		client: Name collisions in this scenario are highly likely,
	likely, even with administrative procedures designed to		even with administrative procedures designed to prevent them.
	prevent them. (This scenario is a popular one in		(This scenario is a popular one in real-world deployments in
	real-world deployments in many types of organizations.)		many types of organizations.) See Section 5 for security
	See Section 7 for security issues with this type of		issues with this type of deployment.
	deployment.
	Scenarios 3 and 4 are much more attractive given some form of		Scenarios 3 and 4 are much more attractive given some form of
	DHCP Authentication, but the difficulties remain.		DHCP Authentication, but the difficulties remain.
	Scenarios 2, 3, and 4 rely on administrative procedures to		Scenarios 2, 3, and 4 rely on administrative procedures to
	ensure name uniqueness for DNS updates, and these procedures may		ensure name uniqueness for DNS updates, and these procedures may
	break down. Experience has shown that, in fact, these pro-		break down. Experience has shown that, in fact, these pro-
	cedures will break down at least occasionally. The question is		cedures will break down at least occasionally. The question is
	what to do when these procedures break down or, for example in		what to do when these procedures break down or, for example in
	scenario #4, may not even exist.		scenario #4, may not even exist.
	skipping to change at page 7, line 50		skipping to change at page 11, line 4
	modes of operation to the administrator of the combined DHCP-DNS		modes of operation to the administrator of the combined DHCP-DNS
	capability: first-update-wins (i.e., the first updating entity		capability: first-update-wins (i.e., the first updating entity
	gets the name) or most-recent-update-wins (i.e., the last updat-		gets the name) or most-recent-update-wins (i.e., the last updat-
	ing entity for a name gets the name).		ing entity for a name gets the name).
	o Multiple DHCP servers		o Multiple DHCP servers
	If multiple DHCP servers are able to update the same DNS zones,		If multiple DHCP servers are able to update the same DNS zones,
	or if DHCP servers are performing A RR updates on behalf of DHCP		or if DHCP servers are performing A RR updates on behalf of DHCP
	clients, and more than one DHCP server may be able to serve		clients, and more than one DHCP server may be able to serve
	addresses to the same DHCP clients, the DHCP servers should be		addresses to the same population of DHCP clients, the DHCP
	able to provide reasonable DNS name update behavior for DHCP		servers should be able to provide reasonable DNS name update
	clients.		behavior for DHCP clients.
	The solution to both of these problems is for the updating entities		The solution to both of these problems is for the updating entities
	(both DHCP clients or DHCP servers) to be able to cooperate when		(either DHCP clients or DHCP servers) to be able to cooperate when
	updating DNS A RRs.		updating DNS A RRs.
	Specifically, a KEY RR, described in [RFC2065] is used to associate		Specifically, a KEY RR, described in [RFC2535] is used to associate
	client ownership information with a DNS name and the A RR associated		client ownership information with a DNS name and the A RR associated
	with that name. When either a client or server adds an A RR for a		with that name. When either a client or server adds an A RR for a
	client, it also adds a KEY RR which specifies a unique client iden-		client, it also adds a KEY RR which specifies a unique client iden-
	tity (based on a "client specifier" created from the client's		tity (based on a "client specifier" created from the client's
	client-id or MAC address: see Appendix A). In this model, only one A		client-id or MAC address: see Appendix A). In this model, only one A
	RR is associated with a given DNS name at a time.		RR is associated with a given DNS name at a time.
	By associating this ownership information with each A RR, cooperating		By associating this ownership information with each A RR, cooperating
	DNS updating entities may determine whether their client is the first		DNS updating entities may determine whether their client is the first
	or last updater of the name (and implement the appropriately config-		or last updater of the name (and implement the appropriately config-
	skipping to change at page 9, line 32		skipping to change at page 12, line 35
	DISCUSSION:		DISCUSSION:
	The updating entity may be configured to allow the existing owner		The updating entity may be configured to allow the existing owner
	to keep the name, and to perform disambiguation on the name of the		to keep the name, and to perform disambiguation on the name of the
	current client in order to attempt to generate a similar but		current client in order to attempt to generate a similar but
	unique name for the current client. In this case, once such a		unique name for the current client. In this case, once such a
	similar name has been generated, the updating entity should res-		similar name has been generated, the updating entity should res-
	tart the process of adding an A RR as specified in this section.		tart the process of adding an A RR as specified in this section.
	3.4.2. 2 Adding PTR RR Entries to DNS		3.4.2. Adding PTR RR Entries to DNS
	The DHCP server submits a DNS query which deletes all of the PTR RRs		The DHCP server submits a DNS query which deletes all of the PTR RRs
	associated with the lease IP address, and adds a PTR RR whose data is		associated with the lease IP address, and adds a PTR RR whose data is
	the client's (possibly disambiguated) host name. The server also adds		the client's (possibly disambiguated) host name. The server also adds
	a KEY RR whose data is the client's client-identity as described in		a KEY RR whose data is the client's client-identity as described in
	Appendix A.		Appendix A.
	3.4.3. Removing Entries from DNS		3.4.3. Removing Entries from DNS
	The first rule in removing DNS entries is be sure that an entity		The first rule in removing DNS entries is be sure that an entity
	removing a DNS entry is only removing an entry that it added.		removing a DNS entry is only removing an entry for which it is
			responsible.
	When a lease expires or a DHCP client issues a DHCPRELEASE request,		When a lease expires or a DHCP client issues a DHCPRELEASE request,
	the DHCP server SHOULD delete the PTR RR that matches the DHCP bind-		the DHCP server SHOULD delete the PTR RR that matches the DHCP bind-
	ing, if one was successfully added. The server's update query SHOULD		ing, if one was successfully added. The server's update query SHOULD
	assert that the name in the PTR record matches the name of the client		assert that the name in the PTR record matches the name of the client
	whose lease has expired or been released.		whose lease has expired or been released.
	The entity chosen to handle the A record for this client (either the		The entity chosen to handle the A record for this client (either the
	client or the server) SHOULD delete the A record that was added when		client or the server) SHOULD delete the A and KEY records that were
	the lease was made to the client.		added when the lease was made to the client.
	In order to perform this delete, the updater prepares an UPDATE query		In order to perform this delete, the updater prepares an UPDATE query
	which contains two prerequisites. The first prerequisite asserts		which contains two prerequisites. The first prerequisite asserts
	that the KEY RR exists whose data is the client identity described in		that the KEY RR exists whose data is the client identity described in
	Appendix A. The second prerequisite asserts that the data in the A RR		Appendix A. The second prerequisite asserts that the data in the A RR
	contains the IP address of the lease that has expired or been		contains the IP address of the lease that has expired or been
	released.		released.
	If the query fails, the updater MUST conclude that it cannot delete		If the query's prerequisites fail, the updater MUST NOT delete the
	the DNS name. It may be that the host whose lease on the server has		DNS name. It may be that the host whose lease on the server has
	expired has moved to another network and obtained a lease from a dif-		expired has moved to another network and obtained a lease from a dif-
	ferent server, which has caused the client's A RR to be replaced. It		ferent server, which has caused the client's A RR to be replaced. It
	may also be that some other client has been configured with a name		may also be that some other client has been configured with a name
	that matches the name of the DHCP client, and the policy was that the		that matches the name of the DHCP client, and the administrative pol-
	last client to specify the name would get the name. In this case,		icy at the site was that the last client to specify the name would
	the KEY RR will no longer match the updater's notion of the client-		get the name. In this case, the KEY RR will no longer match the
	identity of the host pointed to by the DNS name.		updater's notion of the client-identity of the host pointed to by the
			DNS name.
	4. Updating other RRs		4. Updating other RRs
	The procedures described in this document only cover updates to the A		The procedures described in this document only cover updates to the A
	and PTR RRs. Updating other types of RRs is outside the scope of this		and PTR RRs. Updating other types of RRs is outside the scope of this
	document.		document.
	5. Security Considerations		5. Security Considerations
	Whether the client wants to be responsible for updating the FQDN to		Whether the client may be responsible for updating the FQDN to IP
	IP address mapping, or whether the client wants to delegate this		address mapping, or whether the this responsibility lies with the
	responsibility to a server is a local to the client matter. The		DHCP server is a site-local matter. The choice between the two alter-
	choice between the two alternatives may be based on a particular		natives may be based on a particular security model that is used with
	security model that is used with the Dynamic DNS Update protocol		the Dynamic DNS Update protocol (e.g., only a client may have suffi-
	(e.g., only a client may have sufficient credentials to perform		cient credentials to perform updates to the FQDN to IP address map-
	updates to the FQDN to IP address mapping for its FQDN).		ping for its FQDN).
	Whether a DHCP server is always responsible for updating the FQDN to		Whether a DHCP server is always responsible for updating the FQDN to
	IP address mapping (in addition to updating the IP to FQDN mapping),		IP address mapping (in addition to updating the IP to FQDN mapping),
	regarless of the wishes of a DHCP client, is a local to the server		regardless of the wishes of a DHCP client, is also a site-local
	matter. The choice between the two alternatives may be based on a		matter. The choice between the two alternatives may be based on a
	particular security model.		particular security model.
	The client SHOULD use some form of data origin authentication pro-		The client SHOULD use some form of data origin authentication pro-
	cedures (e.g., DNSSEC [DNSSEC]) when performing DNS updates.		cedures (e.g. [TSIG], [DNSSEC]) when performing DNS updates.
	While the DHCP client SHOULD be the one to update the DNS A record,		While the DHCP client MAY be the one to update the DNS A record, in
	in certain specialized cases a DHCP server MAY do so instead. In		certain specialized cases a DHCP server MAY do so instead. In this
	this case, the DHCP server MUST be sure of both the name to use for		case, the DHCP server MUST be sure of both the name to use for the
	the client, as well as the identity of the client.		client, as well as the identity of the client.
	In the general case, both of these conditions are not satisfied --		In the general case, both of these conditions are not satisfied --
	one needs to be mindful of the possibility of MAC address spoofing in		one needs to be mindful of the possibility of MAC address spoofing in
	a DHCP packet. It is not difficult for a DHCP server to know unambi-		a DHCP packet. It is not difficult for a DHCP server to know unambi-
	guously the DNS name to use for a client, but only in certain rela-		guously the DNS name to use for a client, but only in certain cir-
	tively unusual circumstances will the DHCP server know for sure the		cumstances will the DHCP server know for sure the identity of the
	identity of the client. One example of such a circumstance is where		client. If DHCP authentication [DHCPAUTH] becomes widely deployed
	the DHCP client is connected to a network through an MCNS cable		this may become more customary. An example of a situation which
	modem, and the CMTS (head-end) of the cable modem ensures that MAC		offers some extra assurances is one where the DHCP client is con-
	address spoofing simply does not occur.		nected to a network through an MCNS cable modem, and the CMTS (head-
			end) of the cable modem ensures that MAC address spoofing simply does
			not occur.
	Another example where the DHCP server would know the identity of the		Another example where the DHCP server would know the identity of the
	client would be in a case where it was interacting with a remote		client would be in a case where it was interacting with a remote
	access server which encoded a client identification into the DHCP		access server which encoded a client identification into the DHCP
	client-id option. In this case, the remote access server as well as		client-id option. In this case, the remote access server as well as
	the DHCP server would be operating within a trusted environment, and		the DHCP server would be operating within a trusted environment, and
	the DHCP server could trust that the user authentication and authori-		the DHCP server could trust that the user authentication and authori-
	zation procedure of the remote access server was sufficient, and		zation procedure of the remote access server was sufficient, and
	would therefore trust the client identification encoded within the		would therefore trust the client identification encoded within the
	DHCP client-id.		DHCP client-id.
	skipping to change at page 11, line 45		skipping to change at page 14, line 52
	The KEY RR used to hold the DHCP client's identity is formatted as		The KEY RR used to hold the DHCP client's identity is formatted as
	follows:		follows:
	The name of the KEY RR is the name of the A or PTR RR which refers to		The name of the KEY RR is the name of the A or PTR RR which refers to
	the client.		the client.
	The flags field is set to 0x42 - that is, the 1 bit and the 6 bit are		The flags field is set to 0x42 - that is, the 1 bit and the 6 bit are
	set.		set.
	The protocol field is set to 0.		The protocol field is set to [TBD].
	The algorithm field is set to 254.		The algorithm field is set to [TBD].
	The first byte in the key field contains the length of the client-		The first byte in the key field contains the length of the client-
	identity, and is followed by that number of bytes. If a DHCP client		identity, and is followed by that number of bytes of client-identity
	sent the client-id option in its request, the client-identity MUST be		data. If a DHCP client sent the client-id option in its request mes-
	identical to the data in the client-id option. If a client did not		sage, the client-identity MUST be identical to the data in the
	send the client-id option, the client-identity is constructed from		client-id option. If a client did not send the client-id option, the
	the htype byte, the hlen byte, and hlen bytes of the client's chaddr		client-identity is constructed from the htype byte, the hlen byte,
	from its request message.		and hlen bytes of the client's chaddr from its request message.
	7. References		7. References
	[RFC1034] P. Mockapetris, "Domain names - concepts and facilities",		[RFC1034] P. Mockapetris, "Domain names - concepts and facilities",
	RFC1034, 11/01/1987		RFC1034, 11/01/1987
	[RFC1035] P. Mockapetris, "Domain names - implementation and specifi-		[RFC1035] P. Mockapetris, "Domain names - implementation and specif-
	cation", RFC1035, 11/01/1987		ication", RFC1035, 11/01/1987
	[RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC2131,		[RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC2131,
	March 1997		March 1997.
			[RFC2132] S. Alexander, R. Droms, "DHCP Options and BOOTP Vendor
			Extensions", RFC2132, March 1997.
	[RFC1594] A. Marine, J. Reynolds, G. Malkin, "FYI on Questions and		[RFC1594] A. Marine, J. Reynolds, G. Malkin, "FYI on Questions and
	Answer Answers to Commonly asked ``New Internet User''		Answer Answers to Commonly asked ``New Internet User''
	Questions", RFC1594, 03/11/1994		Questions", RFC1594, 03/11/1994
	[DNSSEC]
	[RFC2136] P. Vixie, S. Thomson, Y. Rekhter, J. Bound, "Dynamic		[RFC2136] P. Vixie, S. Thomson, Y. Rekhter, J. Bound, "Dynamic
	Updates in the Domain Name System (DNS UPDATE)", RFC2136,		Updates in the Domain Name System (DNS UPDATE)", RFC2136,
	April 1997		April 1997
	[RFC2119] Bradner, S. "Key words for use in RFCs to Indicate Require-		[RFC2119] Bradner, S. "Key words for use in RFCs to Indicate
	ment Levels", RFC 2119.		Requirement Levels", RFC2119.
	[RFC2065] D. Eastlake, C. Kaufman, "Domain Name System Security		[DNSSEC] D. Eastlake, "Domain Name System Security Extensions",
	Extensions", RFC 2065, January 1997.		RFC2535, March 1999.
			[TSIG] P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington,
			"Secret Key Transaction Signatures for DNS", draft-ietf-
			dnsind-tsig-*, Work in Progress.
			[DHCPAUTH] R. Droms, W. Arbaugh, "Authentication for DHCP Messages",
			draft-ietf-dhc-authentication-*, Work in Progress.
	8. Acknowledgements		8. Acknowledgements
	Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Peter Ford,		Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Robert Elz,
	Edie Gunter, Kim Kinnear, Stuart Kwan, Ted Lemon, Michael Lewis,		Peter Ford, Edie Gunter, R. Barr Hibbs, Kim Kinnear, Stuart Kwan,
	Michael Patton, and Glenn Stump for their review and comments.		Ted Lemon, Michael Lewis, Michael Patton, and Glenn Stump for
			their review and comments.
	9. Author information		9. 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) 235-2128		Phone: (914) 235-2128
	email: yakov@cisco.com		email: yakov@cisco.com
	Mark Stapp		Mark Stapp
	Cisco Systems		Cisco Systems, Inc.
	250 Apollo Drive		250 Apollo Drive
	Chelmsford, MA 01824		Chelmsford, MA 01824
	Phone: (978) 244-8498		Phone: (978) 244-8498
	email: mjs@cisco.com		email: mjs@cisco.com
	10. Full Copyright Statement		10. Full Copyright Statement
	Copyright (C) The Internet Society (1999). All Rights Reserved.		Copyright (C) The Internet Society (1999). All Rights Reserved.
	This document and translations of it may be copied and furnished		This document and translations of it may be copied and furnished
	to others, and derivative works that comment on or otherwise		to others, and derivative works that comment on or otherwise
	explain it or assist in its implmentation may be prepared, copied,		explain it or assist in its implementation may be prepared,
	published and distributed, in whole or in part, without restric-		copied, published and distributed, in whole or in part, without
	tion of any kind, provided that the above copyright notice and		restriction of any kind, provided that the above copyright notice
	this paragraph are included on all such copies and derivative		and this paragraph are included on all such copies and derivative
	works. However, this document itself may not be modified in any		works. However, this document itself may not be modified in any
	way, such as by removing the copyright notice or references to the		way, such as by removing the copyright notice or references to the
	Internet Society or other Internet organizations, except as needed		Internet Society or other Internet organizations, except as needed
	for the purpose of developing Internet standards in which case		for the purpose of developing Internet standards in which case
	the procedures for copyrights defined in the Internet Standards		the procedures for copyrights defined in the Internet Standards
	process must be followed, or as required to translate it into		process must be followed, or as required to translate it into
	languages other than English.		languages other than English.
	The limited permissions granted above are perpetual and will not		The limited permissions granted above are perpetual and will not
	be revoked by the Internet Society or its successors or assigns.		be revoked by the Internet Society or its successors or assigns.
End of changes.
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