wdiff draft-ietf-dhc-dhcp-dns-11.txt draft-ietf-dhc-dhcp-dns-12.txt

DHC Working Group M. Stapp
Internet-Draft Y. Rekhter
Expires: April September 2000 Cisco Systems, Inc.
October, 1999
March 10, 2000

Interaction between DHCP and DNS
<draft-ietf-dhc-dhcp-dns-11.txt>
<draft-ietf-dhc-dhcp-dns-12.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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Abstract

DHCP provides a powerful mechanism for IP host configuration.
However, the configuration capability provided by DHCP does not
include updating DNS, and specifically updating the name to address
and address to name mappings maintained in the DNS.

This document specifies how DHCP clients and servers should use the
Dynamic DNS Updates mechanism in RFC2136[5] to update the DNS name
to address and address to name mappings so that the mappings for
DHCP clients will be consistent with the IP addresses that the
clients acquire via DHCP.

Table of Contents

1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Models of Operation . . . . . . . . . . . . . . . . . . . . 3
4. Client FQDN Option Issues with DDNS in DHCP Environments . . . . . . . . . . . 4
4.1 Name Collisions . . . . . . . . . . 4
4.1 The Flags Field . . . . . . . . . . . . 5
4.2 Multiple DHCP servers . . . . . . . . . . . . . . 5
4.2 The RCODE Fields . . . . . 6
4.3 Use of the DHCID RR . . . . . . . . . . . . . . . . . 6
4.3 The Domain Name Field . . . 6
4.3.1 Format of the DHCID RRDATA . . . . . . . . . . . . . . . . . 6
5. DHCP Client behavior
4.4 DNS RR TTLs . . . . . . . . . . . . . . . . . . . . 6
6. DHCP Server behavior . . . . 8
5. Client FQDN Option . . . . . . . . . . . . . . . . 8
7. Procedures for performing DNS updates . . . . . 8
5.1 The Flags Field . . . . . . 10
7.1 Name Collisions . . . . . . . . . . . . . . . . 9
5.2 The RCODE Fields . . . . . . 10
7.2 Multiple DHCP servers . . . . . . . . . . . . . . . . 10
5.3 The Domain Name Field . . . 11
7.3 Use of the KEY RR . . . . . . . . . . . . . . . . 10
6. DHCP Client behavior . . . . . 11
7.3.1 Format of the KEY RR . . . . . . . . . . . . . . . 10
7. DHCP Server behavior . . . . . . . 12
7.4 DNS RR TTLs . . . . . . . . . . . . . 12
8. Procedures for performing DNS updates . . . . . . . . . . . 12
7.5 14
8.1 Adding A RRs to DNS . . . . . . . . . . . . . . . . . . . . 13
7.6 14
8.2 Adding PTR RR Entries to DNS . . . . . . . . . . . . . . . . 14
7.7 15
8.3 Removing Entries from DNS . . . . . . . . . . . . . . . . . 14
7.8 15
8.4 Updating other RRs . . . . . . . . . . . . . . . . . . . . . 14
8. 16
9. Security Considerations . . . . . . . . . . . . . . . . . . 15
9. 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 17
References . . . . . . . . . . . . . . . . . . . . . . . . . 16 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17 18
Full Copyright Statement . . . . . . . . . . . . . . . . . . 18 19

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 RFC 2119[6].

2. Introduction

DNS RFC1034[1], RFC1035[2] (RFC1034[1], RFC1035[2]) maintains (among other things) the
information about mapping between hosts' Fully Qualified Domain
Names (FQDNs) RFC1594[4] and IP addresses assigned to the hosts. The
information is 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 mapping from an IP address to a FQDN. The Dynamic
DNS Updates specification RFC2136[5] (RFC2136[5]) describes a mechanism that
enables DNS information to be updated over a network.

DHCP RFC2131[3] provides a mechanism by which a host (a DHCP client)
can acquire certain configuration information, along with its IP
address(es). However, DHCP does not provide any mechanisms to 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
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
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
the host's FQDN.

The Dynamic DNS Update protocol can be used to maintain consistency
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
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 reflect the new address. Likewise, when an IP address
is assigned to a host with a particular FQDN, the PTR RR associated
with this address would be updated (using the Dynamic DNS Updates
protocol) to 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 apply for updates to the analogous RR types that are
used when clients are assigned IPv6 addresses via DHCPv6.

3. Models of Operation

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 RR for the acquired address be updated. Therefore, two
separate Dynamic DNS Update transactions occur. Acquiring an address
via DHCP involves two entities: a DHCP client and a DHCP server. In
principle each of these entities could perform none, one, or both of
the transactions. However, in practice not all permutations make
sense. This document covers these possible design permutations:

1. DHCP client updates the A RR, DHCP server updates the PTR RR
2. DHCP server updates both the A and the PTR RRs

The only difference between these two cases is 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 server in both
cases.

The reason these two are important, while others are unlikely, has
to do with authority over the respective DNS domain names. A DHCP
client may be given authority over mapping its own A RRs, or that
authority may be restricted to a server to prevent the client from
listing arbitrary addresses or associating its address with
arbitrary domain names. In all cases, the only reasonable place for
the authority over the PTR RRs associated with the address is in the
DHCP server that allocates the address.

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 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 dynamic DNS updates.

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 may do in cases
where clients do not supply domain names.

4. Client FQDN Option

To Issues with DDNS in DHCP Environments

There are two DNS update the IP address to FQDN mapping a situations that require special
consideration in DHCP environments: cases where more than one DHCP server needs to know
the FQDN of the client to which the server leases the address. To
allow the
client to convey its FQDN to has been configured with the server this document
defines a new DHCP option, called "Client FQDN". The FQDN Option
also contains Flags same FQDN, and RCode fields which cases where more
than one DHCP servers can use server has been given authority to
convey information about perform DNS updates
in a zone. In these cases, it is possible for DNS records to clients.

Clients MAY send the FQDN option, setting appropriate Flags values, be
modified in both their DISCOVER and REQUEST messages. If inconsistent ways unless the updaters have a client sends mechanism
that allows them to detect anomolous situations. If DNS updaters can
detect these situations, site administrators can configure the
FQDN option in its DISCOVER message, it MUST send
updaters' behavior so that the option in
subsequent REQUEST messages.

The code for site's policies can be enforced. We
use the term "Name Collisions" to refer to cases where more than one
DHCP client has been associated with a single FQDN. This
specification describes a mechanism designed to allow updaters to
detect these situations, and requires that DHCP implementations use
this option is 81. Its minimum length is 4.

Code Len Flags RCODE1 RCODE2 Domain Name
+------+------+------+------+------+------+--
| 81 | n | | | | ...
+------+------+------+------+------+------+-- mechanism by default.

4.1 The Flags Field

0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |E|O|S|
+-+-+-+-+-+-+-+-+

When Name Collisions

How can the entity updating an A RR (either the DHCP client or DHCP
server) detect that a domain name has an A RR which is already in
use by a different DHCP client? Similarly, should a DHCP client sends or
server update a domain name which has an A RR that has been
configured by an administrator? In either of these cases, the FQDN option
domain name in question would either have an additional A RR, or
would have its DHCPDISCOVER and/or
DHCPREQUEST messages, it sets original A RR replaced by the new record. Either of
these effects may be considered undesirable by some sites. Different
authority and credential models have different levels of exposure to
name collisions.

1. Client updates A RR, uses Secure DNS Update with credentials
that are associated with the client's FQDN, and exclusive to the
client. Name collisions in this scenario are unlikely (though
not impossible), since the client has received credentials
specific to the name it desires to use. This implies that the
name has already been allocated (through some implementation- or
organization-specific procedure) to that client.

2. Client updates A RR, uses Secure DNS Update with credentials
that are valid for any name in the zone. Name collisions in this
scenario are possible, since the credentials necessary for the
client to update DNS are not necessarily name-specific. Thus,
for the client to be attempting to update a unique name requires
the existence of some administrative procedure to ensure client
configuration with unique names.

3. Server updates the A RR, uses a name for the client which is
known to the server. Name collisions in this scenario are likely
unless prevented by the server's name configuration procedures.
See Section 9 for security issues with this form of deployment.

4. Server updates the A RR, uses a name supplied by the client.
Name collisions in this scenario are highly likely, even with
administrative procedures designed to prevent them. (This
scenario is a popular one in real-world deployments in many
types of organizations.) See Section 9 for security issues with
this type of deployment.

Scenarios 2, 3, and 4 rely on administrative procedures to ensure
name uniqueness for DNS updates, and these procedures may break
down. Experience has shown that, in fact, these procedures will
break down at least occasionally. The question is what to do when
these procedures break down or, for example in scenario #4, may not
even exist.

In all cases of name collisions, the desire is to offer two modes of
operation to the administrator of the combined DHCP-DNS capability:
first-update-wins (i.e., the first updating entity gets the name) or
most-recent-update-wins (i.e., the last updating entity for a name
gets the name).

4.2 Multiple DHCP servers

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
clients, and more than one DHCP server may be able to serve
addresses to the same DHCP clients, the DHCP servers should be able
to provide reasonable and consistent DNS name update behavior for
DHCP clients.

4.3 Use of the DHCID RR

A solution to both of these problems is for the right-most bit (labelled "S") updating entities
(both DHCP clients and DHCP servers) to
indicate be able to detect that it will not perform any Dynamic
another entity has been associated with a DNS updates, name, and that
it expects to offer
administrators the DHCP server opportunity to perform any FQDN-to-IP (the A RR) DNS configure update on its behalf. If this bit behavior.

Specifically, a DHCID RR, described in DHCID RR[12] is clear, the used to
associate client indicates identification information with a DNS name and the
A RR associated with that it intends to maintain its own FQDN-to-IP mapping update.

If name. When either a DHCP client or server intends to take responsibility adds
an A RR for a client, it also adds a DHCID RR which specifies a
unique client identity (based on a "client specifier" created from
the client's client-id or MAC address). In this model, only one A
RR update is associated with a given DNS name at a time.

By associating this ownership information with each A RR,
cooperating DNS updating entities may determine whether or not the their client sending the FQDN option has set
is the "S"
bit, it sets both first or last updater of the "O" bit and name (and implement the "S" bit,
appropriately configured administrative policy), and sends the FQDN
option in its DHCPOFFER and/or DHCPACK messages.

The data in the Domain Name field DHCP clients
which currently have a host name may appear in move from one of two formats:
ASCII, or DNS-style binary encoding (without compression, of
course), as described in RFC1035[2]. A client which sends the FQDN
option MUST set DHCP server to
another without losing their DNS name.

The specific algorithms utilizing the "E" bit DHCID RR to indicate that the data signal client
ownership are explained below. The algorithms only work in the Domain
Name field case
where the updating entities all cooperate -- this approach is DNS-encoded. If a server receives an FQDN option from
a client,
advisory only and intends to include an FQDN option in its reply, is not substitute for DNS security, nor is it
MUST use the same encoding that
replaced by DNS security.

4.3.1 Format of the client used. DHCID RRDATA

The DNS encoding DHCID RR used to hold the DHCP client's identity is
recommended. formatted as
follows:

The use name of ASCII-encoded domain-names the DHCID RR is fragile, and the use name of ASCII encoding in this option should be considered
deprecated. the A or PTR RR which refers
to the DHCP client.

The remaining bits RDATA section of a DHCID RR in transmission contains RDLENGTH
bytes of binary data. From the Flags field are reserved for future
assignment. perspective of DHCP clients and servers which send the FQDN option MUST
set the MBZ bits to 0, and they MUST ignore values in
servers, the part DHC resource record consists of a 16-bit identifier
type, followed by one or more bytes representing the field labelled "MBZ".

4.2 The RCODE Fields

The RCODE1 and RCODE2 fields actual
identifier. There are used by a DHCP server to indicate
to two possible forms for a DHCP client the Response Code from any A or PTR DHCID RR Dynamic DNS
Updates it has performed. 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.

4.3 The Domain Name Field

The Domain Name part of that
is used when the client's link-layer address is being used to
identify it, and one that is used when some DHCP option carries that the FQDN of a
DHCP
client. A client may be configured with a fully-qualified domain
name, or with a partial name that has sent is not fully-qualified. If a
client knows only part of its name, it MAY send a single label,
indicating being used to identify it.

DISCUSSION:
Implementors should note that it knows part of the name but does not necessarily
know actual identifying data is
never placed into the zone in which DNS directly. Instead, the name is to be embedded. The client-identity
data in is used as the
Domain Name field may appear in one input into a one-way hash algorithm, and the
output of two formats: ASCII (with no
terminating NULL), or DNS encoding that hash is then used as DNS RRDATA. This has been
specified in RFC1035[2]. If
the DHCP client wishes order 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 the "E" bit.

A avoid placing data about DHCP client clients that can only send a single label using ASCII encoding
includes a series of ASCII characters in
some sites might consider sensitive into the Domain Name field,
excluding DNS.

When the "." (dot) character. The client SHOULD follow updater is using the
character-set recommendations client's link-layer address, the first
two bytes of RFC1034[1] and RFC1035[2]. A client
using DNS encoding which wants to suggest part the DHCID RRDATA MUST be zero. To generate the rest of its FQDN MAY send
the resource record, the updater MUST compute a non-terminal sequence of labels in one-way hash using
the Domain Name part of MD5[13] algorithm across a buffer containing the
option.

5. DHCP Client behavior

The following describes client's
network hardware type and link-layer address. Specifically, the behavior
first byte of a DHCP client that
implements the Client FQDN option.

If a client that owns/maintains its own FQDN wants to be responsible
for updating buffer contains the FQDN to IP address mapping for network hardware type as it
appears in the FQDN and
address(es) used by DHCP htype field of the client, then client's DHCPREQUEST message.
All of the client MUST include significant bytes of the
Client FQDN option chaddr field in the client's
DHCPREQUEST message originated by follow, in the
client. A DHCP client MAY choose to include same order in which the Client FQDN option bytes
appear in its DISCOVER messages as well as its REQUEST messages. the DHCPREQUEST message. The
rightmost ("S") bit number of significant bytes
in the Flags chaddr field is specified in the option MUST be set to
0. Once hlen field of the client's DHCP configuration
DHCPREQUEST message.

When the updater is completed (the client
receives a DHCPACK message, and successfully completes using a final check
on DHCP option sent by the parameters passed client in its
DHCPREQUEST message, the message), first two bytes of the DHCID RR MUST be the
option code of that option, in network byte order. For example, if
the DHCP client MAY originate
an update for identifier option is being used, the A first byte of
the DHCID RR (associated with should be zero, and the client's FQDN). second byte should be 61
decimal. The
update rest of the DHCID RR MUST be originated contain the results of
computing a one-way hash across the payload of the option being
used, using the MD5 algorithm. The payload of a DHCP option consists
of the bytes of the option following the procedures described in
RFC2136[5], option code and Section 7. If length.

In order for independent DHCP implementations to be able to use the
DHCID RR as a prerequisite in dynamic DNS updates, each updater must
be able to reliably choose the DHCP server from same identifier that any other would
choose. To make this possible, we specify a prioritization which the
will ensure that for any given DHCP client
is requesting a lease includes request, any updater will
select the FQDN option in its ACK message,
and same client-identity data. All updaters MUST use this
order of prioritization by default, but all implementations SHOULD
be configurable to use a different prioritization if so desired by
the server sets both the "S" and site administrators. Because of the "O" (the two rightmost)
bits possibility of future
changes in the option's flags field, the DHCP client MUST NOT initiate
an update protocol, implementors SHOULD check for the name in the Domain Name field.

A client updated
versions of this draft when implementing new DHCP clients and
servers which can choose to delegate the responsibility for updating the
FQDN to IP address mapping for the FQDN perform DDNS updates, and address(es) used by also when releasing new
versions of existing clients and servers.

DHCP clients and servers should use the following forms of client to
identification, starting with the server. In order to inform most preferable, and finishing
with the server least preferable. If the client does not send any of these
forms of identification, the DHCP/DDNS interaction is not defined by
this choice, specification. The most preferable form of identification is
the client SHOULD include Globally Unique Identifier Option [TBD]. Next is the DHCP
Client FQDN option Identifier option. Last is the client's link-layer address,
as conveyed in its DHCPREQUEST message. The rightmost (or "S") bit Implementors should note
that the link-layer address cannot be used if there are no
significant bytes in the Flags chaddr field in of the option
MUST DHCP client's request,
because this does not constitute a unique identifier.

4.4 DNS RR TTLs

RRs associated with DHCP clients may be set more volatile than
statically configured RRs. DHCP clients and servers which perform
dynamic updates should attempt to 1. A client specify resource record TTLs which delegates
reflect this responsibility MUST
NOT attempt volatility, in order to perform a Dynamic DNS update for minimize the name possibility that
there will be stale records in resolvers' caches. A reasonable basis
for RR TTLs is the
Domain Name field lease duration itself: TTLs of the FQDN option. The client MAY supply an FQDN
in the Client FQDN option, 1/2 or 1/3 the
expected lease duration might be reasonable defaults. Because
configured DHCP lease times vary widely from site to site, it may
also be desirable to establish a fixed TTL ceiling. DHCP clients and
servers MAY supply allow administrators to configure the TTLs they will
supply, possibly as a single label (the
most-specific label), fraction of the actual lease time, or it MAY leave that field empty as a signal
to
fixed value.

5. Client FQDN Option

To update the server IP address to generate an FQDN for the client in any manner the
server chooses.

Since there is mapping a possibility that the DHCP server may be configured needs to complete or replace a domain name that know
the client was configured
to send, FQDN of the client might find it useful to send the FQDN option in
its DISCOVER messages. If which the DHCP server returns different Domain
Name data in its OFFER message, leases the address. To
allow the client could use that data in
performing to convey its own eventual A RR update, or in forming the FQDN
option that it sends in its REQUEST message. There is no requirement
that to the client server this document
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 identical the FQDN option data option, setting appropriate Flags values,
in its both their DISCOVER and REQUEST messages. In particular, if If a client has sent sends the
FQDN option to its server, and the configuration of the client changes so
that its notion of in its domain name changes, DISCOVER message, it MAY MUST send the new name
data option in an
subsequent REQUEST messages.

The code for this option is 81. Its minimum length is 4.

Code Len Flags RCODE1 RCODE2 Domain Name
+------+------+------+------+------+------+--
| 81 | n | | | | ...
+------+------+------+------+------+------+--

5.1 The Flags Field

0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |E|O|S|
+-+-+-+-+-+-+-+-+

When a DHCP client sends the FQDN option when in its DHCPDISCOVER and/or
DHCPREQUEST messages, it communicates with sets the server again.
This may allow right-most bit (labelled "S") to
indicate that it will not perform any Dynamic DNS updates, and that
it expects the DHCP server to update the name associated with
the PTR record, and, if the server updated the perform any FQDN-to-IP (the A record representing
the client, to delete that record and attempt an RR) DNS
update for on its behalf. If this bit is clear, the
client's current domain name.

A client indicates
that delegates the responsibility for updating the FQDN it intends to
IP address maintain its own FQDN-to-IP mapping to a server might not receive any indication
(either positive or negative) from the server whether the server was
able to perform the update. In this case the client MAY use

If a DNS
query DHCP server intends to check whether take responsibility for the mapping is updated. A client MUST set RR update
whether or not the RCODE1 and RCODE2 fields in client sending the Client FQDN option to 0 when sending has set the option.

If a client releases its lease prior to "S"
bit, it sets both the lease expiration time "O" bit and the client is responsible for updating "S" bit, and sends the FQDN
option in its A RR, 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), as described in RFC1035[2]. A client
SHOULD delete which sends the A RR (following FQDN
option MUST set the procedures described "E" bit to indicate that the data in
Section 7) associated with the leased address before sending Domain
Name field is DNS binary encoded. If a DHCP
RELEASE message. Similarly, if server receives an FQDN
option from a client was responsible for updating
its A RR, but is unable client, and intends to renew include an FQDN option in its lease,
reply, it MUST use the client SHOULD
attempt to delete same encoding that the A RR before its lease expires. A DHCP client
which has not been able to delete an A RR which it added (because it
has lost used. The DNS
encoding is recommended. The use of ASCII-encoded domain-names is
fragile, and the use of its DHCP IP address) ASCII encoding in this option should attempt to notify
its administrator.

6. DHCP Server behavior

When a server receives a DHCPREQUEST message from a client, if be
considered deprecated.

The remaining bits in the
message contains Flags field are reserved for future
assignment. DHCP clients and servers which send the Client FQDN option, option MUST
set the MBZ bits to 0, and they MUST ignore values in the server replies to part of
the message with field labelled "MBZ".

5.2 The RCODE Fields

The RCODE1 and RCODE2 fields are used by a DHCPACK message, the DHCP server may be configured to
originate an update for indicate
to a DHCP client the Response Code from any A or PTR RR (associated with the address
leased to the client). Any such update MUST be originated following
the procedures described in Section 7. Dynamic DNS
Updates it has performed. The server MAY complete the may also use these fields to
indicate whether it has attempted such an update before the server sends sending the
DHCPACK message message. Each of these fields is one byte long.

Implementors should note that EDNS0 describes a mechanism for
extending the length of a DNS RCODE to 12 bits. EDNS0 is specified
in RFC2671[8]. Only the client. In
this case least-significant 8 bits of the RCODE from the update MUST a
Dynamic DNS Update will be carried to the client in the RCODE1 field of the Client FQDN option in the DHCPACK message.
Alternatively, the server MAY send the DHCPACK message to the client
without waiting for the update DHCP Option.
This provides enough number space to be completed. In this case the
RCODE1 field of accomodate the Client FQDN option RCODEs defined
in the DHCPACK message MUST
be set to 255. Dynamic DNS Update specification.

5.3 The choice between the two alternatives is entirely
determined by Domain Name Field

The Domain Name part of the configuration option carries all or part of the FQDN
of a DHCP server. Servers SHOULD
support both configuration options.

When client. A client may be configured with a server receives 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 DHCPREQUEST message containing single label,
indicating that it knows part of the Client
FQDN option, name but does not necessarily
know the server MUST ignore zone in which the values carried name is to be embedded. The data in the RCODE1
and RCODE2 fields
Domain Name field may appear in one of the option.

In addition, if the Client FQDN option carried two formats: ASCII (with no
terminating NULL), or DNS encoding as specified in RFC1035[2]. If
the DHCPREQUEST
message has DHCP client wishes to use DNS encoding, it MUST set the "S"
third-from-rightmost bit in its the Flags field set, then the server MAY
originate an update for (the "E" bit); if it
uses ASCII encoding, it MUST clear the "E" bit.

A RR (associated with the FQDN carried DHCP client that can only send a single label using ASCII encoding
includes a series of ASCII characters in the option) if it is configured to do so by the site's
administrator, and if it has Domain Name field,
excluding the necessary credentials. "." (dot) character. The server
MAY be configured to use the name supplied in client SHOULD follow the client's
character-set recommendations of RFC1034[1] and RFC1035[2]. A client
using DNS binary encoding which wants to suggest part of its FQDN
option, or it
MAY be configured to modify the supplied name, or
substitute send a different name.

Any such update MUST be originated following the procedures
described non-terminal sequence of labels in Section 7. The server MAY originate the update before
the server sends the DHCPACK message to the client. In this case the
RCODE from the update [RFC2136] MUST be carried to Domain Name part
of the client in option.

6. DHCP Client behavior

The following describes the
RCODE2 field behavior of a DHCP client that
implements the Client FQDN option in the DHCPACK message.
Alternatively the server MAY send the DHCPACK message to the option.

If a client
without waiting that owns/maintains its own FQDN wants to be responsible
for updating the update FQDN to be completed. In this case IP address mapping for the
RCODE2 field of FQDN and
address(es) used by the client, then the client MUST include the
Client FQDN option in the DHCPACK DHCPREQUEST message MUST
be set to 255. The choice between the two alternatives is entirely
up to originated by the
client. A DHCP server. In either case, if the server intends client MAY choose to
perform the DNS update and the client's REQUEST message included the
FQDN option, the server SHOULD include the Client FQDN option
in its ACK
message, and MUST set the "S" DISCOVER messages as well as its REQUEST messages. The
rightmost ("S") bit in the option's Flags field.

Even if field in the Client FQDN option carried in MUST be set to
0. Once the DHCPREQUEST message
has client's DHCP configuration is completed (the client
receives a DHCPACK message, and successfully completes a final check
on the "S" bit parameters passed in its Flags field clear (indicating that the client
wants to update the A RR), message), the server client MAY be configured by the local
administrator to originate
an update for the A RR on (associated with the client's behalf. A FQDN). The
update MUST be originated following the procedures described in
RFC2136[5] and Section 8. If the DHCP server from which the client
is configured to override requesting a lease includes the client's preference SHOULD
include an FQDN option in its ACK message,
and MUST set if the server sets both the "S" and the "O"
and "S" bits (the two
rightmost bits) in the FQDN option's Flags field. The update flags field, the DHCP client MUST be
originated following
NOT initiate an update for the procedures described name in Section 7. The
server MAY originate the update before Domain Name field.

A client can choose to delegate the server sends responsibility for updating the DHCPACK
message
FQDN to IP address mapping for the client. In this case the RCODE from FQDN and address(es) used by the update
[RFC2136] MUST be carried
client to the client in server. In order to inform the RCODE2 field server of this choice,
the client SHOULD include the Client FQDN option in the DHCPACK its DHCPREQUEST
message. Alternatively, the server
MAY send the DHCPACK message to the client without waiting for the
update to be completed. In this case The rightmost (or "S") bit in the RCODE2 Flags field of the Client
FQDN option in the DHCPACK message option
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 DHCP server sends the Client FQDN option 1. A client which delegates this responsibility MUST
NOT attempt to perform a client in the
DHCPACK message, the DHCP server SHOULD send its notion of the
complete FQDN Dynamic DNS update for the client name in the
Domain Name field. field of the FQDN option. The server client MAY simply copy the Domain Name field from supply an FQDN
in the Client FQDN option option, or it MAY supply a single label (the
most-specific label), or it MAY leave that the client sent field empty as a signal
to the server to generate an FQDN for the client in any manner the
server chooses.

Since there is a possibility that the DHCPREQUEST message. The DHCP server MAY may be configured
to complete or modify the replace a domain name
which a that the client sent, or it MAY be was configured
to substitute a
different name. If the server initiates a DDNS update which is not
complete until after send, the server has replied client might find it useful to send the DHCP client, FQDN option in
its DISCOVER messages. If the
server's The DHCP server MUST use the same encoding format (ASCII or
DNS-encoding) that returns different Domain
Name data in its OFFER message, the client used could use that data in
performing its own eventual A RR update, or in forming the FQDN
option that it sends in its
DHCPREQUEST, and MUST set REQUEST message. There is no requirement
that the "E" bit client send identical FQDN option data in the option's Flags field
accordingly.

If its DISCOVER and
REQUEST messages. In particular, if a client's DHCPREQUEST message doesn't carry client has sent the Client FQDN
option (e.g., to its server, and the configuration of the client doesn't implement changes so
that its notion of its domain name changes, it MAY send the Client new name
data in an FQDN option), option when it communicates with the server MAY be configured again.
This may allow the DHCP server to update either or both of the A and name associated with
the PTR RRs. The updates MUST be originated following record, and, if the procedures
described in Section 7.

If a server detects updated the A record representing
the client, to delete that a lease on record and attempt an address update for the
client's current domain name.

A client that delegates the server
leases responsibility for updating the FQDN to
IP address mapping to a client has expired, server might not receive any indication
(either positive or negative) from the server SHOULD delete any PTR RR
which it added via dynamic update. In addition, if whether the server added
an A RR on was
able to perform the client's behalf, update. In this case the server SHOULD also delete client MAY use a DNS
query to check whether the mapping is updated.

A
RR. The deletion client MUST follow set the procedures described RCODE1 and RCODE2 fields in Section 7. the Client FQDN
option to 0 when sending the option.

If a server terminates a client releases its lease on an address prior to the lease's lease expiration time, for instance by sending a DHCPNAK to a client, the
server SHOULD delete any PTR RR which it associated with the address
via DNS Dynamic Update. In addition, if time
and the server took
responsibility client is responsible for an updating its A RR, the server client
SHOULD also delete that the A RR.
The deletion MUST follow RR (following the procedures described in
Section 7.

7. Procedures for performing DNS updates

There are two principal issues that need to be addressed concerning
A RR DNS updates:

7.1 Name Collisions

If 8) associated with the entity leased address before sending a DHCP
RELEASE message. Similarly, if a client was responsible for updating the
its A RR (either RR, but is unable to renew its lease, the DHCP client or DHCP
server) attempts to perform a DNS update SHOULD
attempt to a domain name that has
an delete the A RR which is already in use by a different DHCP client, what
should be done? Similarly, should a before its lease expires. A DHCP client or server update a
domain name
which has an A RR that has not been configured by an
administrator? In either of these cases, the domain name in question
would either have able to delete an additional A RR, or would have its original A RR replaced by which it added (because it
has lost the new record. Either use of these effects may be
considered undesirable in some sites. This specification describes
behavior designed its DHCP IP address) should attempt to prevent these undesirable effects, and requires
that notify
its administrator.

7. DHCP implementations make this Server behavior

When a server receives a DHCPREQUEST message from a client, if the
message contains the default.

1. Client updates A RR, uses DNSSEC. Name collisions in this
scenario are unlikely (though not impossible), since for FQDN option, and the
client server replies to use DNSSEC, it has already received credentials
specific
the message with a DHCPACK message, the server may be configured to
originate an update for the name it desires PTR RR (associated with the address
leased to use. This implies that the
name has already been allocated (through some implementation- or
organization-specific procedure, and presumably uniquely) client). Any such update MUST be originated following
the procedures described in Section 8. The server MAY complete the
update before the server sends the DHCPACK message to
that the client.

2. Client updates A RR, uses some form of TSIG. Name collisions in In
this scenario are possible, since case the credentials necessary for RCODE from the client to update DNS are not necessarily name-specific.
Thus, for the client to MUST be attempting carried to update a unique name
requires the existence of some administrative procedure to
ensure client configuration with unique names.

3. Server updates in
the A RR, uses a name for RCODE1 field of the Client FQDN option in the DHCPACK message.
Alternatively, the server MAY send the DHCPACK message to the client which is
known
without waiting for the update to be completed. In this case the server. Name collisions
RCODE1 field of the Client FQDN option in this scenario are likely
unless prevented the DHCPACK message MUST
be set to 255. The choice between the two alternatives is entirely
determined by the server's name configuration procedures.
See Section 8 for security issues with this form of deployment.

4. Server updates the A RR, uses DHCP server. Servers SHOULD
support both configuration options.

When a name supplied by server receives a DHCPREQUEST message containing the client.
Name collisions Client
FQDN option, the server MUST ignore the values carried in this scenario are highly likely, even with
administrative procedures designed to prevent them. (This
scenario is a popular one the RCODE1
and RCODE2 fields of the option.

In addition, if the Client FQDN option carried in real-world deployments the DHCPREQUEST
message has the "S" bit in many
types of organizations.) See Section 8 its Flags field set, then the server MAY
originate an update for security issues the A RR (associated with
this type of deployment.

Scenarios 3 and 4 are much more attractive given some form of DHCP
Authentication, but difficulties remain.

Scenarios 2, 3, and 4 rely on administrative procedures the FQDN carried
in the option) if it is configured to ensure
name uniqueness for DNS updates, do so by the site's
administrator, and these procedures may break
down. Experience if it has shown that, in fact, these procedures will
break down at least occasionally. the necessary credentials. The question is what server
MAY be configured to use the name supplied in the client's FQDN
option, or it MAY be configured to do when
these modify the supplied name, or
substitute a different name.

Any such update MUST be originated following the procedures break down or, for example
described in scenario #4, may not
even exist.

In all cases of name collisions, Section 8. The server MAY originate the desire is update before
the server sends the DHCPACK message to offer two modes of
operation the client. In this case the
RCODE from the update [RFC2136] MUST be carried to the administrator client in the
RCODE2 field of the combined DHCP-DNS capability:
first-update-wins (i.e., Client FQDN option in the first updating entity gets DHCPACK message.
Alternatively the name) or
most-recent-update-wins (i.e., server MAY send the last updating entity DHCPACK message to the client
without waiting for a name
gets the name).

7.2 Multiple DHCP servers

If multiple DHCP servers are able to update to be completed. In this case the same DNS zones, or
if DHCP servers are performing A RR updates on behalf
RCODE2 field of DHCP
clients, and more than one DHCP server may the Client FQDN option in the DHCPACK message MUST
be able set to serve
addresses 255. The choice between the two alternatives is entirely
up to the same DHCP clients, 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 the "S" bit in its Flags field clear (indicating that the client
wants to update the A RR), the DHCP servers should server MAY be able configured by the local
administrator to provide reasonable and consistent DNS name update behavior for
DHCP clients.

7.3 Use of the KEY A RR on the client's behalf. A solution server
which is configured to override the client's preference SHOULD
include an FQDN option in its ACK message, and MUST set both of these problems is for the updating entities
(both DHCP clients "O"
and DHCP servers) to "S" bits in the FQDN option's Flags field. The update MUST be able to cooperate when
updating DNS A RRs.

Specifically, a KEY RR,
originated following the procedures described in RFC2535[7] is used to associate
client ownership information with a DNS name and Section 8. The
server MAY originate the update before the A RR associated
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
identity (based on a "client specifier" created from sends the client's
client-id or MAC address). DHCPACK
message to the client. In this model, only one A RR is
associated with a given DNS name at a time.

By associating this ownership information with each A RR,
cooperating DNS updating entities may determine whether their client
is the first or last updater of the name (and implement case the
appropriately configured administrative policy), and DHCP clients
which currently have a host name may move RCODE from one DHCP server to
another without losing their DNS name.

The specific algorithms utilizing the KEY RR update
[RFC2136] MUST be carried to signal the client
ownership are explained below. The algorithms only work in the case
where RCODE2 field of the
Client FQDN option in the DHCPACK message. Alternatively, the updating entities all cooperate -- this approach is
advisory only and does not substitute for DNS security, nor is it
replaced by DNS security.

7.3.1 Format of server
MAY send the KEY RR

The KEY RR used DHCPACK message to hold the DHCP client's identity is formatted as
follows:

The name of client without waiting for the KEY RR is
update to be completed. In this case the name RCODE2 field of the A or PTR RR which refers
to Client
FQDN option in the client.

The flags field is DHCPACK message MUST be set to 0x4200 - that is, 255. Whether the 1 bit and
DNS update occurs before or after the 6 bit
are set.

The protocol field DHCPACK is set to [TBD].

The algorithm field sent is set entirely up
to [TBD].

0 15 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Identity-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Client-identity... /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Version field indicates the version of DHCP server's configuration.

When a DHCP server sends the data used in this RR.
The Version field is Client FQDN option to a 2-byte integer client in network byte-order. Its
value MUST be 1.

The remainder of the Key field contains
DHCPACK message, the length DHCP server SHOULD send its notion of the
client-identity, followed by
complete FQDN for the client in the Domain Name field. The server
MAY simply copy the Domain Name field from the Client FQDN option
that number of bytes of client-identity
data. the client sent to the server in the DHCPREQUEST message. The data length is represented as
DHCP server MAY be configured to complete or modify the domain name
which a 2-byte integer in network
byte order. client sent, or it MAY be configured to substitute a
different name. If the server initiates a DDNS update which is not
complete until after the server has replied to the DHCP client, the
server's The server MUST use the same encoding format (ASCII or DNS
binary encoding) that the client sent used in the client-id FQDN option in its
request message, the client-identity
DHCPREQUEST, and MUST be identical to set the data "E" bit in the client-id option. option's Flags field
accordingly.

If a client did not send the client-id
option, client's DHCPREQUEST message doesn't carry the client-identity is constructed from Client FQDN
option (e.g., the htype byte, client doesn't implement the
hlen byte, and hlen bytes of Client FQDN option),
the client's chaddr from its request
message.

7.4 DNS RR TTLs

RRs associated with DHCP clients may server MAY be more volatile than
statically configured RRs. DHCP clients to update either or both of the A and servers which perform
dynamic
PTR RRs. The updates should attempt to specify resource record TTLs which
reflect this volatility, MUST be originated following the procedures
described in order Section 8.

If a server detects that a lease on an address that the server
leases to minimize a client has expired, the possibility that
there will be stale records in resolvers' caches. server SHOULD delete any PTR RR
which it added via dynamic update. In addition, if the server added
an A reasonable basis
for RR TTLs is on the lease duration itself: TTLs of 1/2 or 1/3 client's behalf, the
expected lease duration might be reasonable defaults. Because
configured DHCP lease times vary widely from site to site, it may server SHOULD also be desirable to establish a fixed TTL ceiling. DHCP clients and
servers MAY allow administrators to configure delete the TTLs they will
supply, possibly as A
RR. The deletion MUST follow the procedures described in Section 8.

If a server terminates a fraction of the actual lease on an address prior to the lease's
expiration time, or as for instance by sending a
fixed value.

7.5 DHCPNAK to a client, the
server SHOULD delete any PTR RR which it associated with the address
via DNS Dynamic Update. In addition, if the server took
responsibility for an A RR, the server SHOULD also delete that A RR.
The deletion MUST follow the procedures described in Section 8.

8. Procedures for performing DNS updates

8.1 Adding A RRs to DNS

When a DHCP client or server intends to update an A RR, it first
prepares a DNS UPDATE query which includes as a prerequisite the
assertion that the name does not exist. The update section of the
query attempts to add the new name and its IP address mapping (an A
RR), and the KEY DHCID RR with its unique client-identity.

If this update operation succeeds, the updater can conclude that it
has added a new name whose only RRs are the A and KEY DHCID RR records.
The A RR update is now complete (and a client updater is finished,
while a server might proceed to perform a PTR RR update).

If the first update operation fails with YXDOMAIN, the updater can
conclude that the intended name is in use. The updater then
attempts to confirm that the DNS name is not being used by some
other host. The updater prepares a second UPDATE query in which the
prerequisite is that the desired name has attached to it a KEY DHCID RR
whose contents match the client identity. The update section of
this query deletes the existing A records on the name, and adds the
A record that matches the DHCP binding and the KEY DHCID RR with the
client identity.

If this query succeeds, the updater can conclude that the current
client was the last client associated with the domain name, and that
the name now contains the updated A RR. The A RR update is now
complete (and a client updater is finished, while a server would
then proceed to perform a PTR RR update).

If the second query fails with NXRRSET, the updater must conclude
that the client's desired name is in use by another host. At this
juncture, the updater can decide (based on some administrative
configuration outside of the scope of this document) whether to let
the existing owner of the name keep that name, and to (possibly)
perform some name disambiguation operation on behalf of the current
client, or to replace the RRs on the name with RRs that represent
the current client. If the configured policy allows replacement of
existing records, the updater submits a query that deletes the
existing A RR and the existing KEY DHCID RR, adding A and KEY DHCID RRs that
represent the IP address and client-identity of the new client.

DISCUSSION:
The updating entity may be configured to allow the existing DNS
records on the domain name to remain unchanged, and to perform
disambiguation on the name of the current client in order to
attempt to generate a similar but unique name for the current
client. In this case, once another candidate name has been
generated, the updater should restart the process of adding an A
RR as specified in this section.

7.6

8.2 Adding PTR RR Entries to DNS

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 the client's (possibly disambiguated) host name. The server also
adds a KEY DHCID RR specified in Section 7.3.

7.7 4.3.

8.3 Removing Entries from DNS

The first rule most important consideration in removing DNS entries is be sure
that an entity removing a DNS entry is only removing an entry that
it added. added, or for which an administrator has explicitly assigned it
responsibility.

When a lease expires or a DHCP client issues a DHCPRELEASE request,
the DHCP server SHOULD delete the PTR RR that matches the DHCP
binding, 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 whose lease has expired or been released.

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
the lease was made to the client.

In order to perform this delete, the updater prepares an UPDATE
query which contains two prerequisites. The first prerequisite
asserts that the KEY DHCID RR exists whose data is the client identity
described in Section 7.3. 4.3. The second prerequisite asserts that the
data in the A RR contains the IP address of the lease that has
expired or been released.

If the query fails, the updater MUST NOT delete the 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 different 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 that matches
the name of the DHCP client, and the policy was that the last client
to specify the name would get the name. In this case, the KEY DHCID RR
will no longer match the updater's notion of the client-identity of
the host pointed to by the DNS name.

7.8

8.4 Updating other RRs

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 document.

9. Security Considerations

Unauthenticated updates to the DNS can lead to tremendous confusion,
through malicious attack or through inadvertent misconfiguration.
Administrators should be wary of permitting unsecured DNS updates to
zones which are exposed to the global Internet. Both DHCP clients
and servers SHOULD use some form of update request origin
authentication procedure (e.g., Simple Secure DNS Update[11]) when
performing DNS updates.

Whether the a DHCP client may be responsible for updating the an FQDN to IP
address mapping, or whether the this is the responsibility lies with of the DHCP
server is a site-local matter. The choice between the two
alternatives may be based on a particular the security model that is used with
the Dynamic DNS Update protocol (e.g., only a client may have
sufficient credentials to perform updates to the FQDN to IP address
mapping for its FQDN).

Whether a DHCP server is always responsible for updating the FQDN to
IP address mapping (in addition to updating the IP to FQDN mapping),
regardless of the wishes of a an individual DHCP client, is also a
site-local matter. The choice between the two alternatives may be
based on a particular the security model. Both DHCP clients and servers SHOULD use some form
of update request origin authentication procedure (e.g., TSIG[8],
Simple Secure DNS Update[10]) when performing model that is being used with dynamic DNS
updates.

While the DHCP client MAY be the one to update the DNS A record, in
certain configurations In cases where a DHCP server MAY do so instead. In this
case, is performing DNS updates on
behalf of a client, the DHCP server MUST should be sure of both the DNS name
to use for the client, as well as and of the identity of the client.

In the general case, both of these conditions are

Currently, it is difficult for DHCP servers to
satisfy, develop much
confidence in the identities of its clients, given the absence of security
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 only in certain relatively unusual circumstances will the DHCP
server know for certain the identity of the client. If DHCP authentication[9]
Authentication[10] becomes widely deployed this may become more
customary.

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 modem, and the CMTS (head-end) of the cable modem ensures that
MAC address spoofing simply does not occur. Another example of a
configuration that might be trusted is one where clients obtain
network access via a network access server using PPP. The NAS itself
might be obtaining IP addresses via DHCP, encoding a client
identification into the DHCP client-id option. In this case, the
network access server as well as the DHCP server might be operating
within a trusted environment, in which case the DHCP server could be
configured to trust that the user authentication and authorization
procedure of the remote access server was sufficient, and would
therefore trust the client identification encoded within the DHCP
client-id.

10. Acknowledgements

Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Robert Elz, Peter
Ford, Edie Gunter, Andreas Gustafsson, R. Barr Hibbs, Kim Kinnear,
Stuart Kwan, Ted Lemon, Ed Lewis, Michael Lewis, Josh Littlefield,
Michael Patton, and Glenn Stump for their review and comments.

References

[1] Mockapetris, P., "Domain names - Concepts and Facilities", RFC
1034, Nov 1987.

[2] Mockapetris, P., "Domain names - Implementation and
Specification", RFC 1035, Nov 1987.

[3] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.

[4] Marine, A., Reynolds, J. and G. Malkin, "FYI on Questions and
Answers to Commonly asked ``New Internet User'' Questions", RFC
1594, March 1994.

[5] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
Updates in the Domain Name System", RFC 2136, April 1997.

[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.

[7] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.

[8] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999.

[9] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
"Secret Key Transaction Signatures Authentication for DNS (TSIG)
(draft-ietf-dnsind-tsig-*)",
(draft-ietf-dnsext-tsig-*)", July 1999.

[9]

[10] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages
(draft-ietf-dhc-authentication-*)", June 1999.

[10]

[11] Wellington, B., "Simple Secure DNS Dynamic Updates
(draft-ietf-dnsind-simple-secure-update-*)",
(draft-ietf-dnsext-simple-secure-update-*)", June 1999.

[12] Gustafsson, A., "A DNS RR for encoding DHCP client identity
(draft-ietf-dnsext-dhcid-rr-*)", October 1999.

[13] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,
April 1992.

Authors' Addresses

Mark Stapp
Cisco Systems, Inc.
250 Apollo Dr.
Chelmsford, MA 01824
US

Phone: 978.244.8498
EMail: mjs@cisco.com

Yakov Rekhter
Cisco Systems, Inc.
170 Tasman Dr.
San Jose, CA 95134
US

Phone: 914.235.2128
EMail: yakov@cisco.com

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