draft-ietf-dhc-fqdn-option-12.txt   draft-ietf-dhc-fqdn-option-13.txt 
DHC M. Stapp DHC M. Stapp
Internet-Draft B. Volz Internet-Draft B. Volz
Expires: August 28, 2006 Cisco Systems, Inc. Expires: September 23, 2006 Cisco Systems, Inc.
Y. Rekhter Y. Rekhter
Juniper Networks Juniper Networks
February 24, 2006 March 22, 2006
The DHCP Client FQDN Option The DHCP Client FQDN Option
<draft-ietf-dhc-fqdn-option-12.txt> <draft-ietf-dhc-fqdn-option-13.txt>
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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
skipping to change at page 1, line 36 skipping to change at page 1, line 36
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on August 28, 2006. This Internet-Draft will expire on September 23, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document specifies a Dynamic Host Configuration Protocol for This document describes a Dynamic Host Configuration Protocol for
IPv4, DHCPv4, option which can be used to exchange information about IPv4, DHCPv4, option which can be used to exchange information about
a DHCPv4 client's fully-qualified domain name and about a DHCPv4 client's fully-qualified domain name and about
responsibility for updating the DNS RR related to the client's responsibility for updating the DNS RR related to the client's
address assignment. address assignment.
Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Models of Operation . . . . . . . . . . . . . . . . . . . 3 1.2. Models of Operation . . . . . . . . . . . . . . . . . . . 3
3. The Client FQDN Option . . . . . . . . . . . . . . . . . . . . 4 2. The Client FQDN Option . . . . . . . . . . . . . . . . . . . . 4
3.1. The Flags Field . . . . . . . . . . . . . . . . . . . . . 5 2.1. The Flags Field . . . . . . . . . . . . . . . . . . . . . 5
3.2. The RCODE Fields . . . . . . . . . . . . . . . . . . . . . 6 2.2. The RCODE Fields . . . . . . . . . . . . . . . . . . . . . 6
3.3. The Domain Name Field . . . . . . . . . . . . . . . . . . 6 2.3. The Domain Name Field . . . . . . . . . . . . . . . . . . 6
3.3.1. Deprecated ASCII Encoding . . . . . . . . . . . . . . 7 2.3.1. Deprecated ASCII Encoding . . . . . . . . . . . . . . 7
4. DHCP Client Behavior . . . . . . . . . . . . . . . . . . . . . 7 3. DHCP Client Behavior . . . . . . . . . . . . . . . . . . . . . 7
4.1. Interaction With Other Options . . . . . . . . . . . . . . 7 3.1. Interaction With Other Options . . . . . . . . . . . . . . 7
4.2. Client Desires to Update A RRs . . . . . . . . . . . . . . 8 3.2. Client Desires to Update A RRs . . . . . . . . . . . . . . 8
4.3. Client Desires Server to Do DNS Updates . . . . . . . . . 8 3.3. Client Desires Server to Do DNS Updates . . . . . . . . . 8
4.4. Client Desires No Server DNS Updates . . . . . . . . . . . 8 3.4. Client Desires No Server DNS Updates . . . . . . . . . . . 8
4.5. Domain Name and DNS Update Issues . . . . . . . . . . . . 9 3.5. Domain Name and DNS Update Issues . . . . . . . . . . . . 9
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 9 4. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 9
5.1. When to Perform DNS Updates . . . . . . . . . . . . . . . 10 4.1. When to Perform DNS Updates . . . . . . . . . . . . . . . 10
6. DNS RR TTLs . . . . . . . . . . . . . . . . . . . . . . . . . 11 5. DNS RR TTLs . . . . . . . . . . . . . . . . . . . . . . . . . 11
7. DNS Update Conflicts . . . . . . . . . . . . . . . . . . . . . 12 6. DNS Update Conflicts . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14 10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . . . 17
1. Terminology 1. Introduction
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 [1].
2. Introduction
DNS ([2], [3]) maintains (among other things) the information about DNS ([2], [3]) maintains (among other things) the information about
the mapping between hosts' Fully Qualified Domain Names (FQDNs) [10] the mapping between hosts' Fully Qualified Domain Names (FQDNs) [11]
and IP addresses assigned to the hosts. The information is and IP addresses assigned to the hosts. The information is
maintained in two types of Resource Records (RRs): A and PTR. The maintained in two types of Resource Records (RRs): A and PTR. The
DNS update specification ([4]) describes a mechanism that enables DNS DNS update specification ([4]) describes a mechanism that enables DNS
information to be updated over a network. information to be updated over a network.
The Dynamic Host Configuration Protocol for IPv4 (DHCPv4 or just DHCP The Dynamic Host Configuration Protocol for IPv4 (DHCPv4 or just DHCP
in this document) [5] provides a mechanism by which a host (a DHCP in this document) [5] provides a mechanism by which a host (a DHCP
client) can acquire certain configuration information, along with its client) can acquire certain configuration information, along with its
address. This document specifies a DHCP option, the Client FQDN address. This document specifies a DHCP option, the Client FQDN
option, which can be used by DHCP clients and servers to exchange option, which can be used by DHCP clients and servers to exchange
information about the client's fully-qualified domain name for an information about the client's fully-qualified domain name for an
address and who has the responsibility for updating the DNS with the address and who has the responsibility for updating the DNS with the
associated A and PTR RRs. associated A and PTR RRs.
2.1. Models of Operation 1.1. Terminology
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 [1].
1.2. Models of Operation
When a DHCP client acquires a new address, a site's administrator may When a DHCP client acquires a new address, a site's administrator may
desire that one or both of the A RR for the client's FQDN and the PTR desire that one or both of the A RR for the client's FQDN and the PTR
RR for the acquired address be updated. Therefore, two separate DNS RR for the acquired address be updated. Therefore, two separate DNS
update transactions may occur. Acquiring an address via DHCP update transactions may occur. Acquiring an address via DHCP
involves two entities: a DHCP client and a DHCP server. In principle involves two entities: a DHCP client and a DHCP server. In principle
each of these entities could perform none, one, or both of the each of these entities could perform none, one, or both of the
transactions. However, in practice not all permutations make sense. transactions. However, in practice not all permutations make sense.
The DHCP Client FQDN option is primarily intended to operate in the The DHCP Client FQDN option is primarily intended to operate in the
following two cases: following two cases:
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authority may be restricted to a server to prevent the client from authority may be restricted to a server to prevent the client from
listing arbitrary addresses or associating its address with arbitrary listing arbitrary addresses or associating its address with arbitrary
domain names. In all cases, the only reasonable place for the domain names. In all cases, the only reasonable place for the
authority over the PTR RRs associated with the address is in the DHCP authority over the PTR RRs associated with the address is in the DHCP
server that allocates the address. server that allocates the address.
Note: A third case is supported - the client requests that the server Note: A third case is supported - the client requests that the server
perform no updates. However, this case is presumed to be rare perform no updates. However, this case is presumed to be rare
because of the authority issues. because of the authority issues.
In any case, whether a site permits all, some, or no DHCP servers and It is considered local policy to permit DHCP clients and servers to
clients to perform DNS updates into the zones which it controls is perform DNS updates to zones. This document does not require any
entirely a matter of local administrative policy. This document does specific administrative policy, and does not propose one.
not require any specific administrative policy, and does not propose Furthermore, this specification applies only to DHCP client and
one. The range of possible policies is very broad, from sites where server processes: it does not apply to other processes which initiate
only the DHCP servers have been given credentials that the DNS DNS updates.
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 may support some or all
of these possibilities. Furthermore, this specification applies only
to DHCP client and server processes: it does not apply to other
processes which initiate DNS updates.
This document describes a new DHCP option which a client can use to This document describes a DHCP option which a client can use to
convey all or part of its domain name to a DHCP server. Site- convey all or part of its domain name to a DHCP server. Site-
specific policy determines whether DHCP servers use the names that specific policy determines whether DHCP servers use the names that
clients offer or not, and what DHCP servers may do in cases where clients offer or not, and what DHCP servers may do in cases where
clients do not supply domain names. clients do not supply domain names.
3. The Client FQDN Option 2. The 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
the FQDN of the client to which the server leases the address. To the FQDN of the client to which the server leases the address. To
allow the client to convey its FQDN to the server this document allow the client to convey its FQDN to the server this document
defines a new DHCP option, called "Client FQDN". The Client FQDN defines a new DHCP option, called "Client FQDN". The Client FQDN
option also contains Flags, which DHCP servers can use to convey option also contains Flags, which DHCP servers can use to convey
information about DNS updates to clients, and two deprecated RCODEs. information about DNS updates to clients, and two deprecated RCODEs.
Clients MAY send the Client FQDN option, setting appropriate Flags Clients MAY send the Client FQDN option, setting appropriate Flags
values, in both their DHCPDISCOVER and DHCPREQUEST messages. If a values, in both their DHCPDISCOVER and DHCPREQUEST messages. If a
client sends the Client FQDN option in its DHCPDISCOVER message, it client sends the Client FQDN option in its DHCPDISCOVER message, it
MUST send the option in subsequent DHCPREQUEST messages though the MUST send the option in subsequent DHCPREQUEST messages though the
contents of the option MAY change. contents of the option MAY change.
Only one Client FQDN option MAY appear in a message. Only one Client FQDN option MAY appear in a message, though it may be
instantiated in a message as multiple options [9]. DHCP clients and
servers supporting this option, MUST implement DHCP option
concatenation [9]. In the terminology of [9], the Client FQDN option
is a concatenation-requiring option.
The code for this option is 81. Its minimum length is 3 (octets). The code for this option is 81. Len contains the number of octets
that follow the Len field, and the minimum value is 3 (octets).
The format of the Client FQDN option is: The format of the Client FQDN option is:
Code Len Flags RCODE1 RCODE2 Domain Name Code Len Flags RCODE1 RCODE2 Domain Name
+------+------+------+------+------+------+-- +------+------+------+------+------+------+--
| 81 | n | | | | ... | 81 | n | | | | ...
+------+------+------+------+------+------+-- +------+------+------+------+------+------+--
The above figure follows the conventions of [11]. The above figure follows the conventions of [12].
3.1. The Flags Field 2.1. The Flags Field
The format of the 1-octet Flags field is: The format of the 1-octet Flags field is:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| MBZ |N|E|O|S| | MBZ |N|E|O|S|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The "S" bit indicates whether the server SHOULD or SHOULD NOT perform The "S" bit indicates whether the server SHOULD or SHOULD NOT perform
the A RR (FQDN to address) DNS updates. A client sets the bit to 0 the A RR (FQDN to address) DNS updates. A client sets the bit to 0
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The "N" bit indicates whether the server SHOULD NOT perform any DNS The "N" bit indicates whether the server SHOULD NOT perform any DNS
updates. A client sets this bit to 0 to request that the server updates. A client sets this bit to 0 to request that the server
SHOULD perform updates (the PTR RR and possibly the A RR based on the SHOULD perform updates (the PTR RR and possibly the A RR based on the
"S" bit) or to 1 to request that the server SHOULD NOT perform any "S" bit) or to 1 to request that the server SHOULD NOT perform any
DNS updates. A server sets the "N" bit to indicate whether the DNS updates. A server sets the "N" bit to indicate whether the
server SHALL (0) or SHALL NOT (1) perform DNS updates. If the "N" server SHALL (0) or SHALL NOT (1) perform DNS updates. If the "N"
bit is 1, the "S" bit MUST be 0. bit is 1, the "S" bit MUST be 0.
The "E" bit indicates the encoding of the Domain Name field. 1 The "E" bit indicates the encoding of the Domain Name field. 1
indicates DNS-style binary encoding, without compression, as indicates canonical wire format, without compression, as described in
described in RFC 1035 [3]. This encoding SHOULD be used by clients [3], section 3.1. This encoding SHOULD be used by clients and MUST
and MUST be supported by servers. 0 indicates a now deprecated ASCII be supported by servers. 0 indicates a now deprecated ASCII encoding
encoding (see Section 3.3.1). A server MUST use the same encoding as (see Section 2.3.1). A server MUST use the same encoding as that
that used by the client. A server that does not support the used by the client. A server that does not support the deprecated
deprecated ASCII encoding MUST ignore Client FQDN options that use ASCII encoding MUST ignore Client FQDN options that use that
that encoding. encoding.
The remaining bits in the Flags field are reserved for future The remaining bits in the Flags field are reserved for future
assignment. DHCP clients and servers which send the Client FQDN assignment. DHCP clients and servers which send the Client FQDN
option MUST clear the MBZ bits, and they MUST ignore these bits. option MUST clear the MBZ bits, and they MUST ignore these bits.
3.2. The RCODE Fields 2.2. The RCODE Fields
The RCODE1 and RCODE2 fields are deprecated. A client SHOULD set The two 1-octet RCODE1 and RCODE2 fields are deprecated. A client
these to 0 when sending the option and SHOULD ignore them on receipt. SHOULD set these to 0 when sending the option and SHOULD ignore them
A server SHOULD set these to 255 when sending the option and MUST on receipt. A server SHOULD set these to 255 when sending the option
ignore them on receipt. and MUST ignore them on receipt.
As this option with these fields is already in wide use, the fields As this option with these fields is already in wide use, the fields
are retained. These fields were originally defined for use by a DHCP are retained. These fields were originally defined for use by a DHCP
server to indicate to a DHCP client the Response Code from any A server to indicate to a DHCP client the Response Code from any A
(RCODE1) or PTR (RCODE2) RR DNS updates it has performed or a value (RCODE1) or PTR (RCODE2) RR DNS updates it has performed or a value
of 255 was used to indicate that an update had been initiated but had of 255 was used to indicate that an update had been initiated but had
not yet completed. Each of these fields is one octet long. These not yet completed. Each of these fields is one octet long. These
fields were defined before EDNS0 [12], which describes a mechanism fields were defined before EDNS0 [13], which describes a mechanism
for extending the length of a DNS RCODE to 12 bits, which is another for extending the length of a DNS RCODE to 12 bits, which is another
reason to deprecate them. reason to deprecate them.
If the client needs to confirm the DNS update has been done, it MAY If the client needs to confirm the DNS update has been done, it MAY
use a DNS query to check whether the mapping is up to date. However, use a DNS query to check whether the mapping is up to date. However,
depending on the load on the DHCP and DNS servers and the DNS depending on the load on the DHCP and DNS servers and the DNS
propagation delays, the client can only infer success. If the propagation delays, the client can only infer success. If the
information is not found to be up to date in DNS, the servers might information is not found to be up to date in DNS, the authoritative
not have completed the updates or zone transfers, or not yet updated servers might not have completed the updates or zone transfers, or
their caches. caching resolvers may yet have updated their caches.
3.3. The Domain Name Field 2.3. The Domain Name Field
The Domain Name part of the option carries all or part of the FQDN of The Domain Name part of the option carries all or part of the FQDN of
a DHCP client. The data in the Domain Name field SHOULD appear in a DHCP client. The data in the Domain Name field SHOULD appear in
uncompressed DNS encoding as specified in RFC 1035 [3]. If the DHCP canonical wire format as specified in [3], section 3.1. If the DHCP
client uses DNS encoding, it MUST set to 1 the "E" bit in the Flags client uses the canonical wire format, it MUST set the "E" bit in the
field. In order to determine whether the FQDN has changed between Flags field to 1. In order to determine whether the FQDN has changed
message exchanges, the client and server MUST NOT alter the Domain between message exchanges, the client and server MUST NOT alter the
Name field contents unless the FQDN has actually changed. Domain Name field contents unless the FQDN has actually changed.
A client MAY be configured with a fully-qualified domain name or with 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 a partial name that is not fully-qualified. If a client knows only
part of its name, it MAY send a name that is not fully-qualified, part of its name, it MAY send a name that is not fully-qualified,
indicating that it knows part of the name but does not necessarily indicating that it knows part of the name but does not necessarily
know the zone in which the name is to be embedded. know the zone in which the name is to be embedded.
To send a fully-qualified domain name, the Domain Name field is set To send a fully-qualified domain name, the Domain Name field is set
to the DNS encoded domain name including the terminating zero-length to the DNS encoded domain name including the terminating zero-length
label. To send a partial name, the Domain Name field is set to the label. To send a partial name, the Domain Name field is set to the
DNS encoded domain name without the terminating zero-length label. DNS encoded domain name without the terminating zero-length label.
A client MAY also leave the Domain Name field empty if it desires the A client MAY also leave the Domain Name field empty if it desires the
server to provide a name. server to provide a name.
3.3.1. Deprecated ASCII Encoding 2.3.1. Deprecated ASCII Encoding
A substantial population of clients implemented an earlier draft A substantial population of clients implemented an earlier draft
version of this specification, which permitted an ASCII encoding of version of this specification, which permitted an ASCII encoding of
the Domain Name field. Server implementations SHOULD be aware that the Domain Name field. Server implementations SHOULD be aware that
clients which send the Client FQDN option with the "E" bit set to 0 clients which send the Client FQDN option with the "E" bit set to 0
are using an ASCII encoding of the Domain Name field. Servers MAY be are using an ASCII encoding of the Domain Name field. Servers MAY be
prepared to return an ASCII encoded version of the Domain Name field prepared to return an ASCII encoded version of the Domain Name field
to such clients. Servers that are not prepared to return an ASCII to such clients. Servers that are not prepared to return an ASCII
encoded version MUST ignore the Client FQDN option if the "E" bit is encoded version MUST ignore the Client FQDN option if the "E" bit is
0. The use of ASCII encoding in this option SHOULD be considered 0. The use of ASCII encoding in this option SHOULD be considered
deprecated. deprecated.
A DHCP client which used ASCII encoding was permitted to suggest a A DHCP client which used ASCII encoding was permitted to suggest a
single label if it was not configured with a fully-qualified name. single label if it was not configured with a fully-qualified name.
Such clients send a single label as a series of ASCII characters in Such clients send a single label as a series of ASCII characters in
the Domain Name field, excluding the "." (dot) character. the Domain Name field, excluding the "." (dot) character.
Clients and servers SHOULD follow the character set rules of RFC 952 Clients and servers SHOULD follow the character set rules of [6]RFC
[6], fourth section ("Assumptions"), first 5 sentences, as modified 952, fourth section ("Assumptions"), first 5 sentences, as modified
by RFC 1123 [7] section 2.1. However, implementers SHOULD also be by [7] section 2.1. However, implementers SHOULD also be aware that
aware that some client software may send data intended to be in other some client software may send data intended to be in other character
character sets. This specification does not require support for sets. This specification does not require support for other
other character sets. character sets.
4. DHCP Client Behavior 3. DHCP Client Behavior
The following describes the behavior of a DHCP client that implements The following describes the behavior of a DHCP client that implements
the Client FQDN option. the Client FQDN option.
4.1. Interaction With Other Options 3.1. Interaction With Other Options
Other DHCP options MAY carry data that is related to the Domain Name Other DHCP options MAY carry data that is related to the Domain Name
field of the Client FQDN option. The Host Name option [11], for field of the Client FQDN option. The Host Name option [12], for
example, contains an ASCII string representation of the client's host example, contains an ASCII string representation of the client's host
name. In general, a client does not need to send redundant data, and name. In general, a client does not need to send redundant data, and
therefore clients which send the Client FQDN option in their messages therefore clients which send the Client FQDN option in their messages
MUST NOT also send the Host Name option. Clients which receive both MUST NOT also send the Host Name option. Clients which receive both
the Host Name option and the Client FQDN option from a server SHOULD the Host Name option and the Client FQDN option from a server SHOULD
prefer Client FQDN option data. Section 5 instructs servers to prefer Client FQDN option data. Section 4 instructs servers to
ignore the Host Name option in client messages which include the ignore the Host Name option in client messages which include the
Client FQDN option. Client FQDN option.
4.2. Client Desires to Update A RRs 3.2. Client Desires to Update A RRs
If a client that owns/maintains its 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, the client MUST include the Client address(es) used by the client, the client MUST include the Client
FQDN option in the DHCPREQUEST message originated by the client. A FQDN option in the DHCPREQUEST message originated by the client. A
DHCP client MAY choose to include the Client FQDN option in its DHCP client MAY choose to include the Client FQDN option in its
DHCPDISCOVER messages as well as its DHCPREQUEST messages. The "S" DHCPDISCOVER messages as well as its DHCPREQUEST messages. The "S",
bit in the Flags field in the option MUST be 0. The "O" and "N" bits "O", and "N" bits in the Flags field in the option MUST be 0.
MUST be 0.
Once the client's DHCP configuration is completed (the client Once the client's DHCP configuration is completed (the client
receives a DHCPACK message and successfully completes a final check receives a DHCPACK message and successfully completes a final check
on the parameters passed in the message), the client MAY originate an on the parameters passed in the message), the client MAY originate an
update for the A RR (associated with the client's FQDN) unless the update for the A RR (associated with the client's FQDN) unless the
server has set the "S" bit to 1. If the "S" is 1, the DHCP client server has set the "S" bit to 1. If the "S" is 1, the DHCP client
SHOULD NOT initiate an update for the name in the server's returned SHOULD NOT initiate an update for the name in the server's returned
Client FQDN option Domain Name field. However, a DHCP client that is Client FQDN option Domain Name field. However, a DHCP client that is
explicitly configured with a FQDN MAY ignore the state of the "S" bit explicitly configured with a FQDN MAY ignore the state of the "S" bit
if the server's returned name matches the client's configured name. if the server's returned name matches the client's configured name.
4.3. Client Desires Server to Do DNS Updates 3.3. Client Desires Server to Do DNS Updates
A client can choose to delegate the responsibility for updating the A client can choose to delegate the responsibility for updating the
FQDN to IP address mapping for the FQDN and address(es) used by the FQDN to IP address mapping for the FQDN and address(es) used by the
client to the server. In order to inform the server of this choice, client to the server. In order to inform the server of this choice,
the client SHOULD include the Client FQDN option in its DHCPREQUEST the client SHOULD include the Client FQDN option in its DHCPREQUEST
message and MAY include the Client FQDN option in its DHCPDISCOVER. message and MAY include the Client FQDN option in its DHCPDISCOVER.
The "S" bit in the Flags field in the option MUST be 1. The "O" and The "S" bit in the Flags field in the option MUST be 1 and the "O"
"N" bits MUST be 0. and "N" bits MUST be 0.
4.4. Client Desires No Server DNS Updates 3.4. Client Desires No Server DNS Updates
A client can choose to request that the server perform no DNS updates A client can choose to request that the server perform no DNS updates
on its behalf. In order to inform the server of this choice, the on its behalf. In order to inform the server of this choice, the
client SHOULD include the Client FQDN option in its DHCPREQUEST client SHOULD include the Client FQDN option in its DHCPREQUEST
message and MAY include the Client FQDN option in its DHCPDISCOVER. message and MAY include the Client FQDN option in its DHCPDISCOVER.
The "N" bit in the Flags field in the option MUST be 1 and the "S" The "N" bit in the Flags field in the option MUST be 1 and the "S"
and "O" bits MUST be 0. and "O" bits MUST be 0.
Once the client's DHCP configuration is completed (the client Once the client's DHCP configuration is completed (the client
receives a DHCPACK message and successfully completes a final check receives a DHCPACK message and successfully completes a final check
on the parameters passed in the message), the client MAY originate on the parameters passed in the message), the client MAY originate
its DNS updates provided the server's "N" bit is 1. If the server's its DNS updates provided the server's "N" bit is 1. If the server's
"N" bit is 0, the server MAY perform the PTR RR updates; and, MAY "N" bit is 0, the server MAY perform the PTR RR updates; and, MAY
also perform the A RR updates if the "S" bit is 1. also perform the A RR updates if the "S" bit is 1.
4.5. Domain Name and DNS Update Issues 3.5. Domain Name and DNS Update Issues
As there is a possibility that the DHCP server is configured to As there is a possibility that the DHCP server is configured to
complete or replace a domain name that the client sends, the client complete or replace a domain name that the client sends, the client
MAY find it useful to send the Client FQDN option in its DHCPDISCOVER MAY find it useful to send the Client FQDN option in its DHCPDISCOVER
messages. If the DHCP server returns different Domain Name data in messages. If the DHCP server returns different Domain Name data in
its DHCPOFFER message, the client could use that data in performing its DHCPOFFER message, the client could use that data in performing
its own eventual A RR update, or in forming the Client FQDN option its own eventual A RR update, or in forming the Client FQDN option
that it sends in its DHCPREQUEST message. There is no requirement that it sends in its DHCPREQUEST message. There is no requirement
that the client send identical Client FQDN option data in its that the client send identical Client FQDN option data in its
DHCPDISCOVER and DHCPREQUEST messages. In particular, if a client DHCPDISCOVER and DHCPREQUEST messages. In particular, if a client
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it MAY send the new name data in a Client FQDN option when it it MAY send the new name data in a Client FQDN option when it
communicates with the server again. This MAY cause the DHCP server communicates with the server again. This MAY cause the DHCP server
to update the name associated with the PTR record, and, if the 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 updated the A record representing the client, to delete that record
and attempt an update for the client's current domain name. and attempt an update for the client's current domain name.
A client that delegates the responsibility for updating the FQDN to A client that delegates the responsibility for updating the FQDN to
IP address mapping to a server will not receive any indication IP address mapping to a server will not receive any indication
(either positive or negative) from the server whether the server was (either positive or negative) from the server whether the server was
able to perform the update. The client MAY use a DNS query to check able to perform the update. The client MAY use a DNS query to check
whether the mapping is up to date (see Section 3.2). whether the mapping is up to date (see Section 2.2).
If a client releases its lease prior to the lease expiration time and If a client releases its lease prior to the lease expiration time and
the client is responsible for updating its A RR, the client SHOULD the client is responsible for updating its A RR, the client SHOULD
delete the A RR associated with the leased address before sending a delete the A RR associated with the leased address before sending a
DHCPRELEASE message. Similarly, if a client was responsible for DHCPRELEASE message. Similarly, if a client was responsible for
updating its A RR, but is unable to renew its lease, the client 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 DHCP SHOULD attempt to delete the A RR before its lease expires. A DHCP
client which has not been able to delete an A RR which it added client which has not been able to delete an A RR which it added
(because it has lost the use of its DHCP IP address) SHOULD attempt (because it has lost the use of its DHCP IP address) SHOULD attempt
to notify its administrator, perhaps by emitting a log message. to notify its administrator, perhaps by emitting a log message.
A client that desires to perform DNS updates to A RRs SHOULD NOT do A client that desires to perform DNS updates to A RRs SHOULD NOT do
so if the client's address is a private address [8]. so if the client's address is a private address [8].
5. DHCP Server Behavior 4. DHCP Server Behavior
The following describes the behavior of a DHCP server that implements The following describes the behavior of a DHCP server that implements
the Client FQDN option when the client's message includes the Client the Client FQDN option when the client's message includes the Client
FQDN option. FQDN option.
The server examines its configuration and the Flag bits in the The server examines its configuration and the Flag bits in the
client's Client FQDN option to determine how to respond: client's Client FQDN option to determine how to respond:
o If the client's "E" bit is 0 and the server does not support ASCII o If the client's "E" bit is 0 and the server does not support ASCII
encoding (Section 3.3.1), the server SHOULD ignore the Client FQDN encoding (Section 2.3.1), the server SHOULD ignore the Client FQDN
option. option.
o The server sets to 0 the "S", "O", and "N" Flag bits in its copy o The server sets to 0 the "S", "O", and "N" bits in its copy of the
of the option it will return to the client. The server copies the option it will return to the client. The server copies the
client's "E" bit. client's "E" bit.
o If the client's "N" bit is 1 and the server's configuration allows o If the client's "N" bit is 1 and the server's configuration allows
it to honor the client's request for no server initiated DNS it to honor the client's request for no server initiated DNS
updates, the server sets the "N" bit to 1. updates, the server sets the "N" bit to 1.
o Otherwise, if the client's "S" bit is 1 and the server's o Otherwise, if the client's "S" bit is 1 and the server's
configuration allows it to honor the client's request for the configuration allows it to honor the client's request for the
server to initiate A RR DNS updates, the server sets the "S" to 1. server to initiate A RR DNS updates, the server sets the "S" to 1.
If the server's "S" bit does not match the client's "S" bit, the If the server's "S" bit does not match the client's "S" bit, the
server sets the "O" bit to 1. server sets the "O" bit to 1.
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used in the Client FQDN option in its DHCPDISCOVER or DHCPREQUEST, used in the Client FQDN option in its DHCPDISCOVER or DHCPREQUEST,
and MUST set the "E" bit in the option's Flags field accordingly. and MUST set the "E" bit in the option's Flags field accordingly.
If a client sends both the Client FQDN and Host Name option, the If a client sends both the Client FQDN and Host Name option, the
server SHOULD ignore the Host Name option. server SHOULD ignore the Host Name option.
The server SHOULD set the RCODE1 and RCODE2 fields to 255 before The server SHOULD set the RCODE1 and RCODE2 fields to 255 before
sending the Client FQDN message to the client in a DHCPOFFER or sending the Client FQDN message to the client in a DHCPOFFER or
DHCPACK. DHCPACK.
5.1. When to Perform DNS Updates 4.1. When to Perform DNS Updates
The server SHOULD NOT perform any DNS updates if the "N" bit is 1 in The server SHOULD NOT perform any DNS updates if the "N" bit is 1 in
the Flags field of the Client FQDN option in the DHCPACK messages (to the Flags field of the Client FQDN option in the DHCPACK messages (to
be) sent to the client. However, the server SHOULD delete any RRs be) sent to the client. However, the server SHOULD delete any RRs
which it previously added via DNS updates for the client. which it previously added via DNS updates for the client.
The server MAY perform the PTR RR DNS update (unless the "N" bit is The server MAY perform the PTR RR DNS update (unless the "N" bit is
1). 1).
The server MAY perform the A RR DNS update if the "S" bit is 1 in the The server MAY perform the A RR DNS update if the "S" bit is 1 in the
Flags field of the Client FQDN option in the DHCPACK message (to be) Flags field of the Client FQDN option in the DHCPACK message (to be)
sent to the client. sent to the client.
The server MAY perform these updates even if the client's DHCPREQUEST The server MAY perform these updates even if the client's DHCPREQUEST
did not carry the Client FQDN option. The server MUST NOT initiate did not carry the Client FQDN option. The server MUST NOT initiate
DNS updates when responding to DHCPDISCOVER messages from a client. DNS updates when responding to DHCPDISCOVER messages from a client.
The server MAY complete its DNS updates (PTR RR or PTR and A RR) The server MAY perform its DNS updates (PTR RR or PTR and A RR)
before the server sends the DHCPACK message to the client. before or after sending the DHCPACK message to the client.
Alternatively, the server MAY send the DHCPACK message to the client
without waiting for the update to be completed. Whether the DNS
update occurs before or after the DHCPACK is sent is entirely up to
the DHCP server's configuration.
If the server's A RR DNS update does not complete until after the If the server's A RR DNS update does not complete until after the
server has replied to the DHCP client, the server's interaction with server has replied to the DHCP client, the server's interaction with
the DNS server MAY cause the DHCP server to change the domain name the DNS server MAY cause the DHCP server to change the domain name
that it associates with the client. This can occur, for example, if that it associates with the client. This can occur, for example, if
the server detects and resolves a domain-name conflict [9]. In such the server detects and resolves a domain-name conflict [10]. In such
cases, the domain name that the server returns to the DHCP client cases, the domain name that the server returns to the DHCP client
would change between two DHCP exchanges. would change between two DHCP exchanges.
If the server previously performed DNS updates for the client and the If the server previously performed DNS updates for the client and the
client's information has not changed, the server MAY skip performing client's information has not changed, the server MAY skip performing
additional DNS updates. additional DNS updates.
When a server detects that a lease on an address that the server When a server detects that a lease on an address that the server
leases to a client has expired, the server SHOULD delete any PTR RR leases to a client has expired, the server SHOULD delete any PTR RR
which it added via DNS update. In addition, if the server added an A which it added via DNS update. In addition, if the server added an A
RR on the client's behalf, the server SHOULD also delete the A RR. RR on the client's behalf, the server SHOULD also delete the A RR.
When a server terminates a lease on an address prior to the lease's When a server terminates a lease on an address prior to the lease's
expiration time, for instance by sending a DHCPNAK to a client, the expiration time, for instance by sending a DHCPNAK to a client, the
server SHOULD delete any PTR RR which it associated with the address server SHOULD delete any PTR RR which it associated with the address
via DNS update. In addition, if the server took responsibility for via DNS update. In addition, if the server took responsibility for
an A RR, the server SHOULD also delete that A RR. an A RR, the server SHOULD also delete that A RR.
6. DNS RR TTLs 5. DNS RR TTLs
RRs associated with DHCP clients may be more volatile than statically RRs associated with DHCP clients may be more volatile than statically
configured RRs. DHCP clients and servers that perform dynamic configured RRs. DHCP clients and servers that perform dynamic
updates should attempt to specify resource record TTLs which reflect updates should attempt to specify resource record TTLs which reflect
this volatility, in order to minimize the possibility that answers to this volatility, in order to minimize the possibility that answers to
DNS queries will return records that refer to DHCP IP address DNS queries will return records that refer to DHCP IP address
assignments that have expired or been released. assignments that have expired or been released.
The coupling among primary, secondary, and caching DNS servers is The coupling among primary, secondary, and caching DNS servers is
'loose'; that is a fundamental part of the design of the DNS. This 'loose'; that is a fundamental part of the design of the DNS. This
looseness makes it impossible to prevent all possible situations in looseness makes it impossible to prevent all possible situations in
which a resolver may return a record reflecting a DHCP assigned IP which a resolver may return a record reflecting a DHCP assigned IP
address that has expired or been released. In deployment, this address that has expired or been released. In deployment, this
rarely, if ever, represents a significant problem. Most DHCP-managed rarely, if ever, represents a significant problem. Most DHCP-managed
clients are infrequently looked-up by name in the DNS, and the clients are infrequently looked-up by name in the DNS, and the
deployment of IXFR (RFC 1995 [15]) and NOTIFY (RFC 1996 [16]) can deployment of IXFR ([16]) and NOTIFY ([17]) can reduce the latency
reduce the latency between updates and their visibility at secondary between updates and their visibility at secondary servers.
servers.
We suggest these basic guidelines for implementers. In general, the We suggest these basic guidelines for implementers. In general, the
TTLs for RRs added as a result of DHCP IP address assignment activity TTLs for RRs added as a result of DHCP IP address assignment activity
SHOULD be less than the initial lease time. The RR TTL on a DNS SHOULD be less than the initial lease time. The RR TTL on a DNS
record added SHOULD NOT exceed 1/3 of the lease time, and SHOULD be record added SHOULD NOT exceed 1/3 of the lease time, but SHOULD NOT
at least 10 minutes. We recognize that individual administrators be less than 10 minutes. We recognize that individual administrators
will have varying requirements: DHCP servers and clients SHOULD allow will have varying requirements: DHCP servers and clients SHOULD allow
administrators to configure TTLs and upper and lower bounds on the administrators to configure TTLs and upper and lower bounds on the
TTL values, either as an absolute time interval or as a percentage of TTL values, either as an absolute time interval or as a percentage of
the lease time. the lease time.
While clients and servers MAY update the TTL of the records as the While clients and servers MAY update the TTL of the records as the
lease is about to expire, there is no requirement that they do so as lease is about to expire, there is no requirement that they do so as
this puts additional load on the DNS system with likely little this puts additional load on the DNS system with likely little
benefit. benefit.
7. DNS Update Conflicts 6. DNS Update Conflicts
This document does not resolve how a DHCP client or server prevent This document does not resolve how a DHCP client or server prevent
name conflicts. This document addresses only how a DHCP client and name conflicts. This document addresses only how a DHCP client and
server negotiate who will perform the DNS updates and the fully server negotiate who will perform the DNS updates and the fully
qualified domain name requested or used. qualified domain name requested or used.
Implementers of this work will need to consider how name conflicts Implementers of this work will need to consider how name conflicts
will be prevented. If a DNS updater needs a security token in order will be prevented. If a DNS updater needs a security token in order
to successfully perform DNS updates on a specific name, name to successfully perform DNS updates on a specific name, name
conflicts can only occur if multiple updaters are given a security conflicts can only occur if multiple updaters are given a security
token for that name. Or, if the fully qualified domains are based on token for that name. Or, if the fully qualified domains are based on
the specific address bound to a client, conflicts will not occur. the specific address bound to a client, conflicts will not occur.
Or, a name conflict resolution technique as described in "Resolving Or, a name conflict resolution technique as described in "Resolving
Name Conflicts" [9]) SHOULD be used. Name Conflicts" [10]) SHOULD be used.
8. IANA Considerations 7. IANA Considerations
IANA has already assigned DHCP option 81 to the Client FQDN option. IANA has already assigned DHCP option 81 to the Client FQDN option.
As this document updates the option's use, IANA is requested to As this document describes the option's use, IANA is requested to
reference this document for option 81. reference this document for option 81.
9. Security Considerations 8. Security Considerations
Unauthenticated updates to the DNS can lead to tremendous confusion, Unauthenticated updates to the DNS can lead to tremendous confusion,
through malicious attack or through inadvertent misconfiguration. through malicious attack or through inadvertent misconfiguration.
Administrators need to be wary of permitting unsecured DNS updates to Administrators need to be wary of permitting unsecured DNS updates to
zones which are exposed to the global Internet. Both DHCP clients zones which are exposed to the global Internet. Both DHCP clients
and servers should use some form of update request origin and servers should use some form of update request origin
authentication procedure (e.g., Secure DNS Dynamic Update [13]) when authentication procedure (e.g., Secure DNS Dynamic Update [14]) when
performing DNS updates. performing DNS updates.
Whether a DHCP client is responsible for updating an FQDN to IP Whether a DHCP client is responsible for updating an FQDN to IP
address mapping or whether this is the responsibility of the DHCP address mapping or whether this is the responsibility of the DHCP
server is a site-local matter. The choice between the two server is a site-local matter. The choice between the two
alternatives is likely based on the security model that is used with alternatives is likely based on the security model that is used with
the DNS update protocol (e.g., only a client may have sufficient the DNS update protocol (e.g., only a client may have sufficient
credentials to perform updates to the FQDN to IP address mapping for credentials to perform updates to the FQDN to IP address mapping for
its FQDN). its FQDN).
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cases where a DHCP server is performing DNS updates on behalf of a cases where a DHCP server is performing DNS updates on behalf of a
client, the DHCP server should be sure of the DNS name to use for the client, the DHCP server should be sure of the DNS name to use for the
client, and of the identity of the client. client, and of the identity of the client.
Currently, it is difficult for DHCP servers to develop much Currently, it is difficult for DHCP servers to develop much
confidence in the identities of its clients, given the absence of confidence in the identities of its clients, given the absence of
entity authentication from the DHCP protocol itself. There are many entity authentication from the DHCP protocol itself. There are many
ways for a DHCP server to develop a DNS name to use for a client, but ways for a DHCP server to develop a DNS name to use for a client, but
only in certain relatively unusual circumstances will the DHCP server only in certain relatively unusual circumstances will the DHCP server
know for certain the identity of the client. If DHCP Authentication know for certain the identity of the client. If DHCP Authentication
[14] becomes widely deployed this may become more customary. [15] becomes widely deployed this may become more customary.
One example of a situation which offers some extra assurances is one One example of a situation which offers some extra assurances is one
where the DHCP client is connected to a network through an MCNS cable where the DHCP client is connected to a network through an MCNS cable
modem, and the CMTS (head-end) ensures that MAC address spoofing modem, and the CMTS (head-end) ensures that MAC address spoofing
simply does not occur. Another example of a configuration that might simply does not occur. Another example of a configuration that might
be trusted is one where clients obtain network access via a network be trusted is one where clients obtain network access via a network
access server using PPP. The NAS itself might be obtaining IP access server using PPP. The NAS itself might be obtaining IP
addresses via DHCP, encoding a client identification into the DHCP addresses via DHCP, encoding a client identification into the DHCP
client-id option. In this case, the network access server as well as client-id option. In this case, the network access server as well as
the DHCP server might be operating within a trusted environment, in the DHCP server might be operating within a trusted environment, in
which case the DHCP server could be configured to trust that the user which case the DHCP server could be configured to trust that the user
authentication and authorization procedure of the remote access authentication and authorization procedure of the remote access
server was sufficient, and would therefore trust the client server was sufficient, and would therefore trust the client
identification encoded within the DHCP client-id. identification encoded within the DHCP client-id.
It is critical to implement proper conflict resolution, and the It is critical to implement proper conflict resolution, and the
security considerations of conflict resolution apply [9]. security considerations of conflict resolution apply [10].
10. Acknowledgements 9. Acknowledgements
Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Robert Elz, Peter Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Robert Elz, Peter
Ford, Olafur Gudmundsson, Edie Gunter, Andreas Gustafsson, David W. Ford, Olafur Gudmundsson, Edie Gunter, Andreas Gustafsson, David W.
Hankins, R. Barr Hibbs, Kim Kinnear, Stuart Kwan, Ted Lemon, Ed Hankins, R. Barr Hibbs, Kim Kinnear, Stuart Kwan, Ted Lemon, Ed
Lewis, Michael Lewis, Josh Littlefield, Michael Patton, Pekka Savola, Lewis, Michael Lewis, Josh Littlefield, Michael Patton, Pekka Savola,
Jyrki Soini, and Glenn Stump for their review and comments. Jyrki Soini, and Glenn Stump for their review and comments.
11. References 10. References
11.1. Normative References 10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Mockapetris, P., "Domain names - concepts and facilities", [2] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[3] Mockapetris, P., "Domain names - implementation and [3] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
skipping to change at page 14, line 46 skipping to change at page 14, line 39
[6] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet host [6] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet host
table specification", RFC 952, October 1985. table specification", RFC 952, October 1985.
[7] Braden, R., "Requirements for Internet Hosts - Application and [7] Braden, R., "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, October 1989. Support", STD 3, RFC 1123, October 1989.
[8] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. [8] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E.
Lear, "Address Allocation for Private Internets", BCP 5, Lear, "Address Allocation for Private Internets", BCP 5,
RFC 1918, February 1996. RFC 1918, February 1996.
[9] Stapp, M. and B. Volz, "Resolution of DNS Name Conflicts Among [9] Lemon, T. and S. Cheshire, "Encoding Long Options in the
Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
November 2002.
[10] Stapp, M. and B. Volz, "Resolution of DNS Name Conflicts Among
DHCP Clients (draft-ietf-dhc-ddns-resolution-*.txt)", DHCP Clients (draft-ietf-dhc-ddns-resolution-*.txt)",
February 2006. February 2006.
11.2. Informative References 10.2. Informative References
[10] Marine, A., Reynolds, J., and G. Malkin, "FYI on Questions and [11] Marine, A., Reynolds, J., and G. Malkin, "FYI on Questions and
Answers - Answers to Commonly asked "New Internet User" Answers - Answers to Commonly asked "New Internet User"
Questions", RFC 1594, March 1994. Questions", RFC 1594, March 1994.
[11] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor [12] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. Extensions", RFC 2132, March 1997.
[12] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, [13] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999. August 1999.
[13] Wellington, B., "Secure Domain Name System (DNS) Dynamic [14] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000. Update", RFC 3007, November 2000.
[14] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", [15] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001. RFC 3118, June 2001.
[15] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, [16] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
August 1996. August 1996.
[16] Vixie, P., "A Mechanism for Prompt Notification of Zone Changes [17] Vixie, P., "A Mechanism for Prompt Notification of Zone Changes
(DNS NOTIFY)", RFC 1996, August 1996. (DNS NOTIFY)", RFC 1996, August 1996.
Authors' Addresses Authors' Addresses
Mark Stapp Mark Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
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