draft-ietf-dhc-ddns-resolution-12.txt   rfc4703.txt 
Dynamic Host Configuration M. Stapp Network Working Group M. Stapp
Internet-Draft B. Volz Request for Comments: 4703 B. Volz
Expires: September 23, 2006 Cisco Systems, Inc. Category: Standards Track Cisco Systems, Inc.
March 22, 2006 October 2006
Resolution of FQDN Conflicts among DHCP Clients
<draft-ietf-dhc-ddns-resolution-12.txt>
Status of this Memo
By submitting this Internet-Draft, each author represents that any
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
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at Resolution of Fully Qualified Domain Name (FQDN) Conflicts
http://www.ietf.org/ietf/1id-abstracts.txt. among Dynamic Host Configuration Protocol (DHCP) Clients
The list of Internet-Draft Shadow Directories can be accessed at Status of This Memo
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 23, 2006. This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
DHCP provides a mechanism for host configuration that includes The Dynamic Host Configuration Protocol (DHCP) provides a mechanism
dynamic assignment of IP addresses and fully qualified domain names. for host configuration that includes dynamic assignment of IP
To maintain accurate name to IP address and IP address to name addresses and fully qualified domain names. To maintain accurate
mappings in the DNS, these dynamically assigned addresses and fully name-to-IP-address and IP-address-to-name mappings in the DNS, these
qualified domain names require updates to the DNS. This document dynamically assigned addresses and fully qualified domain names
identifies situations in which conflicts in the use of fully (FQDNs) require updates to the DNS. This document identifies
qualified domain names may arise among DHCP clients and servers, and situations in which conflicts in the use of fully qualified domain
describes a strategy for the use of the DHCID DNS resource record in names may arise among DHCP clients and servers, and it describes a
strategy for the use of the DHCID DNS resource record (RR) in
resolving those conflicts. resolving those conflicts.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology .....................................................3
3. Issues with DNS Update in DHCP Environments . . . . . . . . . 3 3. Issues with DNS Update in DHCP Environments .....................4
3.1. Client Misconfiguration . . . . . . . . . . . . . . . . . 4 3.1. Client Misconfiguration ....................................4
3.2. Multiple DHCP Servers . . . . . . . . . . . . . . . . . . 5 3.2. Multiple DHCP Servers ......................................5
4. Use of the DHCID RR . . . . . . . . . . . . . . . . . . . . . 5 4. Use of the DHCID RR .............................................5
5. Procedures for Performing DNS Updates . . . . . . . . . . . . 6 5. Procedures for Performing DNS Updates ...........................6
5.1. Error Return Codes . . . . . . . . . . . . . . . . . . . . 6 5.1. Error Return Codes .........................................6
5.2. Dual IPv4/IPv6 Client Considerations . . . . . . . . . . . 6 5.2. Dual IPv4/IPv6 Client Considerations .......................6
5.3. Adding A and/or AAAA RRs to DNS . . . . . . . . . . . . . 7 5.3. Adding A and/or AAAA RRs to DNS ............................7
5.3.1. Initial DHCID RR Request . . . . . . . . . . . . . . . 7 5.3.1. Initial DHCID RR Request ............................7
5.3.2. DNS UPDATE When FQDN in Use . . . . . . . . . . . . . 7 5.3.2. DNS UPDATE When FQDN in Use .........................7
5.3.3. FQDN in Use by another Client . . . . . . . . . . . . 8 5.3.3. FQDN in Use by Another Client .......................8
5.4. Adding PTR RR Entries to DNS . . . . . . . . . . . . . . . 8 5.4. Adding PTR RR Entries to DNS ...............................8
5.5. Removing Entries from DNS . . . . . . . . . . . . . . . . 9 5.5. Removing Entries from DNS ..................................9
5.6. Updating Other RRs . . . . . . . . . . . . . . . . . . . . 9 5.6. Updating Other RRs ........................................10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations ........................................10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgements ...............................................11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8. References .....................................................11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References ......................................11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11 8.2. Informative References ....................................11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
1. Introduction 1. Introduction
"The Client FQDN Option" [8] includes a description of the operation "The Client FQDN Option" [8] includes a description of the operation
of [4] clients and servers that use the DHCPv4 client FQDN option. of [4] clients and servers that use the DHCPv4 client FQDN option.
And, "The DHCPv6 Client FQDN Option" [9] includes a description of "The DHCPv6 Client FQDN Option" [9] includes a description of the
the operation of [5] clients and servers that use the DHCPv6 client operation of [5] clients and servers that use the DHCPv6 client FQDN
FQDN option. Through the use of the client FQDN option, DHCP clients option. Through the use of the client FQDN option, DHCP clients and
and servers can negotiate the client's FQDN and the allocation of servers can negotiate the client's FQDN and the allocation of
responsibility for updating the DHCP client's A and/or AAAA RRs. responsibility for updating the DHCP client's A and/or AAAA RRs.
This document identifies situations in which conflicts in the use of This document identifies situations in which conflicts in the use of
FQDNs may arise among DHCP clients and servers, and describes a FQDNs may arise among DHCP clients and servers, and it describes a
strategy for the use of the DHCID DNS resource record [2] in strategy for the use of the DHCID DNS resource record [2] in
resolving those conflicts. resolving those conflicts.
In any case, whether a site permits all, some, or no DHCP servers and In any case, whether a site permits all, some, or no DHCP servers and
clients to perform DNS updates ([3], [10]) into the zones that it clients to perform DNS updates ([3], [10]) into the zones that it
controls is entirely a matter of local administrative policy. This controls is entirely a matter of local administrative policy. This
document does not require any specific administrative policy, and document does not require any specific administrative policy, and
does not propose one. The range of possible policies is very broad, does not propose one. The range of possible policies is very broad,
from sites where only the DHCP servers have been given credentials from sites where only the DHCP servers have been given credentials
that the DNS servers will accept, to sites where each individual DHCP that the DNS servers will accept, to sites where each individual DHCP
skipping to change at page 3, line 42 skipping to change at page 3, line 42
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1]. document are to be interpreted as described in [1].
This document assumes familiarity with DNS terminology defined in [6] This document assumes familiarity with DNS terminology defined in [6]
and DHCP terminology defined in [4] and [5]. and DHCP terminology defined in [4] and [5].
FQDN, or Fully Qualified Domain Name, is the full name of a system, FQDN, or Fully Qualified Domain Name, is the full name of a system,
rather than just its hostname. For example, "venera" is a hostname rather than just its hostname. For example, "venera" is a hostname,
and "venera.isi.edu" is an FQDN. See [7]. and "venera.isi.edu" is an FQDN. See [7].
DOCSIS, or Data-Over-Cable Service Interface Specifications, is DOCSIS, or Data-Over-Cable Service Interface Specifications, is
defined by CableLabs (www.cablelabs.com). defined by CableLabs.
3. Issues with DNS Update in DHCP Environments 3. Issues with DNS Update in DHCP Environments
There are two DNS update situations that require special There are two DNS update situations that require special
consideration in DHCP environments: cases where more than one DHCP consideration in DHCP environments: cases where more than one DHCP
client has been configured with the same FQDN and cases where more client has been configured with the same FQDN, and cases where more
than one DHCP server has been given authority to perform DNS updates than one DHCP server has been given authority to perform DNS updates
in a zone. In these cases, it is possible for DNS records to be in a zone. In these cases, it is possible for DNS records to be
modified in inconsistent ways unless the updaters have a mechanism modified in inconsistent ways unless the updaters have a mechanism
that allows them to detect anomalous situations. If DNS updaters can that allows them to detect anomalous situations. If DNS updaters can
detect these situations, site administrators can configure the detect these situations, site administrators can configure the
updaters' behavior so that the site's policies can be enforced. This updaters' behavior so that the site's policies can be enforced. This
specification describes a mechanism designed to allow updaters to specification describes a mechanism designed to allow updaters to
detect these situations, and suggests that DHCP implementations use detect these situations and suggests that DHCP implementations use
this mechanism by default. this mechanism by default.
3.1. Client Misconfiguration 3.1. Client Misconfiguration
Administrators may wish to maintain a one-to-one relationship between Administrators may wish to maintain a one-to-one relationship between
active DHCP clients and FQDNs, and to maintain consistency between a active DHCP clients and FQDNs, and to maintain consistency between a
client's A, AAAA, and PTR RRs. Clients that are not represented in client's A, AAAA, and PTR RRs. Clients that are not represented in
the DNS, or clients that inadvertently share an FQDN with another the DNS, or clients that inadvertently share an FQDN with another
client may encounter inconsistent behavior or may not be able to client may encounter inconsistent behavior or may not be able to
obtain access to network resources. Whether each DHCP client is obtain access to network resources. Whether each DHCP client is
configured with a FQDN by its administrator or whether the DHCP configured with an FQDN by its administrator or whether the DHCP
server is configured to distribute the clients' FQDN, the consistency server is configured to distribute the clients' FQDN, the consistency
of the DNS data is entirely dependent on the accuracy of the of the DNS data is entirely dependent on the accuracy of the
configuration procedure. Sites that deploy [10] may configure configuration procedure. Sites that deploy [10] may configure
credentials for each client and its assigned FQDN in a way that is credentials for each client and its assigned FQDN in a way that is
more error-resistant, as both the FQDN and credentials must match. more error-resistant, as both the FQDN and credentials must match.
Consider an example in which two DHCP clients in the "example.com" Consider an example in which two DHCP clients in the "example.com"
network are both configured with the hostname "foo". The clients are network are both configured with the hostname "foo". The clients are
permitted to perform their own DNS updates. The first client, client permitted to perform their own DNS updates. The first client, client
A, is configured via DHCP. It adds an A RR to "foo.example.com", and A, is configured via DHCP. It adds an A RR to "foo.example.com", and
skipping to change at page 4, line 47 skipping to change at page 4, line 51
configured via DHCP, and it also begins to update "foo.example.com". configured via DHCP, and it also begins to update "foo.example.com".
At this point, the "example.com" administrators may wish to establish At this point, the "example.com" administrators may wish to establish
some policy about DHCP clients' FQDNs. If the policy is that each some policy about DHCP clients' FQDNs. If the policy is that each
client that boots should replace any existing A RR that matches its client that boots should replace any existing A RR that matches its
FQDN, Client B can proceed, though Client A may encounter problems. FQDN, Client B can proceed, though Client A may encounter problems.
In this example, Client B replaces the A RR associated with In this example, Client B replaces the A RR associated with
"foo.example.com". Client A must have some way to recognize that the "foo.example.com". Client A must have some way to recognize that the
RR associated with "foo.example.com" now contains information for RR associated with "foo.example.com" now contains information for
Client B, so that it can avoid modifying the RR. When Client A's Client B, so that it can avoid modifying the RR. When Client A's
assigned IP address expires, for example, it should not remove a RR assigned IP address expires, for example, it should not remove an RR
that reflects Client B's DHCP assigned IP address. that reflects Client B's DHCP-assigned IP address.
If the policy is that the first DHCP client with a given FQDN should If the policy is that the first DHCP client with a given FQDN should
be the only client associated with that FQDN, Client B needs to be be the only client associated with that FQDN, Client B needs to be
able to determine if it is not the client associated with able to determine if it is not the client associated with
"foo.example.com". It could be that Client A booted first, and that "foo.example.com". It could be that Client A booted first, and that
Client B should choose another FQDN. Or it could be that B has Client B should choose another FQDN. Or it could be that B has
booted on a new subnet, and received a new IP address assignment, in booted on a new subnet and received a new IP address assignment, in
which case B should update the DNS with its new IP address. It must which case B should update the DNS with its new IP address. It must
either retain persistent state about the last IP address it was either retain persistent state about the last IP address it was
assigned (in addition to its current IP address) or it must have some assigned (in addition to its current IP address) or it must have some
other way to detect that it was the last updater of "foo.example.com" other way to detect that it was the last updater of "foo.example.com"
in order to implement the site's policy. in order to implement the site's policy.
3.2. Multiple DHCP Servers 3.2. Multiple DHCP Servers
It is possible to arrange for DHCP servers to perform A and/or AAAA It is possible to arrange for DHCP servers to perform A and/or AAAA
RR updates on behalf of their clients. If a single DHCP server RR updates on behalf of their clients. If a single DHCP server
manages all of the DHCP clients at a site, it can maintain a database manages all of the DHCP clients at a site, it can maintain a database
of the FQDNs in use, and can check that database before assigning a of the FQDNs in use and can check that database before assigning an
FQDN to a client. Such a database is necessarily proprietary, FQDN to a client. Such a database is necessarily proprietary,
however, and the approach does not work once more than one DHCP however, and the approach does not work once more than one DHCP
server is deployed. server is deployed.
When multiple DHCP servers are deployed, the servers require a way to When multiple DHCP servers are deployed, the servers require a way to
coordinate the identities of DHCP clients. Consider an example in coordinate the identities of DHCP clients. Consider an example in
which DHCPv4 Client A boots, obtains an IP address from Server S1, which DHCPv4 Client A boots, obtains an IP address from Server S1,
presenting the hostname "foo" in a Client FQDN option [8] in its presenting the hostname "foo" in a Client FQDN option [8] in its
DHCPREQUEST message. Server S1 updates the FQDN "foo.example.com", DHCPREQUEST message. Server S1 updates the FQDN "foo.example.com",
adding an A RR containing the IP address assigned to A. The client adding an A RR containing the IP address assigned to A. The client
then moves to another subnet, served by Server S2. When Client A then moves to another subnet, served by Server S2. When Client A
boots on the new subnet, Server S2 will assign it a new IP address, boots on the new subnet, Server S2 will assign it a new IP address
and will attempt to add an A RR containing the newly assigned IP and will attempt to add an A RR containing the newly assigned IP
address to the FQDN "foo.example.com". At this point, without some address to the FQDN "foo.example.com". At this point, without some
communication mechanism which S2 can use to ask S1 (and every other communication mechanism that S2 can use to ask S1 (and every other
DHCP server that updates the zone) about the client, S2 has no way to DHCP server that updates the zone) about the client, S2 has no way to
know whether Client A is currently associated with the FQDN, or know whether Client A is currently associated with the FQDN, or
whether A is a different client configured with the same FQDN. If whether A is a different client configured with the same FQDN. If
the servers cannot distinguish between these situations, they cannot the servers cannot distinguish between these situations, they cannot
enforce the site's naming policies. enforce the site's naming policies.
4. Use of the DHCID RR 4. Use of the DHCID RR
A solution to both of these problems is for the updater (a DHCP A solution to both of these problems is for the updater (a DHCP
client or DHCP server) to be able to determine which DHCP client has client or DHCP server) to be able to determine which DHCP client has
been associated with a FQDN, in order to offer administrators the been associated with an FQDN, in order to offer administrators the
opportunity to configure updater behavior. opportunity to configure updater behavior.
For this purpose, a DHCID RR, specified in [2], is used to associate For this purpose, a DHCID RR, specified in [2], is used to associate
client identification information with a FQDN and the A, AAAA, and client identification information with an FQDN and the A, AAAA, and
PTR RRs associated with that FQDN. When either a client or server PTR RRs associated with that FQDN. When either a client or server
adds A, AAAA, or PTR RRs for a client, it also adds a DHCID RR that adds A, AAAA, or PTR RRs for a client, it also adds a DHCID RR that
specifies a unique client identity, based on data from the client's specifies a unique client identity, based on data from the client's
DHCP message. In this model, only one client is associated with a DHCP message. In this model, only one client is associated with a
given FQDN at a time. given FQDN at a time.
By associating this ownership information with each FQDN, cooperating By associating this ownership information with each FQDN, cooperating
DNS updaters may determine whether their client is currently DNS updaters may determine whether their client is currently
associated with a particular FQDN and implement the appropriately associated with a particular FQDN and implement the appropriately
configured administrative policy. In addition, DHCP clients which configured administrative policy. In addition, DHCP clients that
currently have FQDNs may move from one DHCP server to another without currently have FQDNs may move from one DHCP server to another without
losing their FQDNs. losing their FQDNs.
The specific algorithm utilizing the DHCID RR to signal client The specific algorithm utilizing the DHCID RR to signal client
ownership is explained below. The algorithm only works in the case ownership is explained below. The algorithm only works in the case
where the updating entities all cooperate -- this approach is where the updating entities all cooperate -- this approach is
advisory only and is not a substitute for DNS security, nor is it advisory only and is not a substitute for DNS security, nor is it
replaced by DNS security. replaced by DNS security.
5. Procedures for Performing DNS Updates 5. Procedures for Performing DNS Updates
skipping to change at page 6, line 34 skipping to change at page 6, line 38
5.1. Error Return Codes 5.1. Error Return Codes
Certain RCODEs defined in [3] indicate that the destination DNS Certain RCODEs defined in [3] indicate that the destination DNS
server cannot perform an update, i.e., FORMERR, SERVFAIL, REFUSED, server cannot perform an update, i.e., FORMERR, SERVFAIL, REFUSED,
NOTIMP. If one of these RCODEs is returned, the updater MUST NOTIMP. If one of these RCODEs is returned, the updater MUST
terminate its update attempt. Other RCODEs [13] may indicate that terminate its update attempt. Other RCODEs [13] may indicate that
there are problems with the key being used and may mean to try a there are problems with the key being used and may mean to try a
different key, if available, or to terminate the operation. Because different key, if available, or to terminate the operation. Because
some errors may indicate a misconfiguration of the updater or the DNS some errors may indicate a misconfiguration of the updater or the DNS
server, the updater MAY attempt to signal to its administrator that server, the updater MAY attempt to signal to its administrator that
an error has occurred, e.g. through a log message. an error has occurred, e.g., through a log message.
5.2. Dual IPv4/IPv6 Client Considerations 5.2. Dual IPv4/IPv6 Client Considerations
At the time of publication of this document, a small minority of DHCP At the time of publication of this document, a small minority of DHCP
clients support both IPv4 and IPv6. We anticipate, however, that a clients support both IPv4 and IPv6. We anticipate, however, that a
transition will take place over a period of time, and more sites will transition will take place over a period of time, and more sites will
have dual-stack clients present. IPv6 clients require updates of have dual-stack clients present. IPv6 clients require updates of
AAAA RRs; IPv4 client require updates of A RRs. The administrators AAAA RRs; IPv4 client require updates of A RRs. The administrators
of mixed deployments will likely wish to permit a single FQDN to of mixed deployments will likely wish to permit a single FQDN to
contain A and AAAA RRs from the same client. contain A and AAAA RRs from the same client.
Sites that wish to permit a single FQDN to contain both A and AAAA Sites that wish to permit a single FQDN to contain both A and AAAA
RRs MUST make use of DHCPv4 clients and servers that support using RRs MUST make use of DHCPv4 clients and servers that support using
the DHCP Unique Identifier (DUID) for DHCPv4 client identifiers such the DHCP Unique Identifier (DUID) for DHCPv4 client identifiers such
that this DUID is used in computing the RDATA of the DHCID RR by both that this DUID is used in computing the RDATA of the DHCID RR by both
DHCPv4 and DHCPv6 for the client, see [11]. Otherwise, a dual-stack DHCPv4 and DHCPv6 for the client; see [11]. Otherwise, a dual-stack
client that uses older-style DHCPv4 client identifiers (see [4] and client that uses older-style DHCPv4 client identifiers (see [4] and
[12]) will only be able to have either its A or AAAA records in DNS [12]) will only be able to have either its A or AAAA records in DNS
under a single FQDN because of the DHCID RR conflicts that result. under a single FQDN because of the DHCID RR conflicts that result.
5.3. Adding A and/or AAAA RRs to DNS 5.3. Adding A and/or AAAA RRs to DNS
When a DHCP client or server intends to update A and/or AAAA RRs, it When a DHCP client or server intends to update A and/or AAAA RRs, it
starts with the UPDATE request in Section 5.3.1. starts with the UPDATE request in Section 5.3.1.
As the update sequence below can result in loops, implementers SHOULD As the update sequence below can result in loops, implementers SHOULD
skipping to change at page 7, line 43 skipping to change at page 7, line 45
update (see Section 5.1). update (see Section 5.1).
5.3.2. DNS UPDATE When FQDN in Use 5.3.2. DNS UPDATE When FQDN in Use
The updater next attempts to confirm that the FQDN is not being used The updater next attempts to confirm that the FQDN is not being used
by some other client by preparing an UPDATE request in which there by some other client by preparing an UPDATE request in which there
are two prerequisites. The first prerequisite is that the FQDN are two prerequisites. The first prerequisite is that the FQDN
exists. The second is that the desired FQDN has attached to it a exists. The second is that the desired FQDN has attached to it a
DHCID RR whose contents match the client identity. The update DHCID RR whose contents match the client identity. The update
section of the UPDATE request contains: section of the UPDATE request contains:
1. A delete of any existing A RRs on the FQDN if this is an A update 1. A delete of any existing A RRs on the FQDN if this is an A update
or an AAAA update and the updater does not desire A records on or an AAAA update and the updater does not desire A records on
the FQDN or this update is adding an A and the updater only the FQDN, or if this update is adding an A and the updater only
desires a single IP address on the FQDN. desires a single IP address on the FQDN.
2. A delete of the existing AAAA RRs on the FQDN if the updater does 2. A delete of the existing AAAA RRs on the FQDN if the updater does
not desire AAAA records on the FQDN or this update is adding an not desire AAAA records on the FQDN, or if this update is adding
AAAA and the updater only desires a single IP address on the an AAAA and the updater only desires a single IP address on the
FQDN. FQDN.
3. An add (or adds) of the A RR that matches the DHCP binding if 3. An add (or adds) of the A RR that matches the DHCP binding if
this is an A update. this is an A update.
4. Adds of the AAAA RRs that match the DHCP bindings if this is an 4. Adds of the AAAA RRs that match the DHCP bindings if this is an
AAAA update. AAAA update.
Whether A or AAAA RRs are deleted depends on the updater or updater's Whether A or AAAA RRs are deleted depends on the updater or updater's
policy. For example, if the updater is the client or configured as policy. For example, if the updater is the client or configured as
the only DHCP server for the link on which the client is located, the the only DHCP server for the link on which the client is located, the
updater may find it beneficial to delete all A and/or AAAA RRs and updater may find it beneficial to delete all A and/or AAAA RRs and
then add the current set of A and/or AAAA RRs, if any, for the then add the current set of A and/or AAAA RRs, if any, for the
client. client.
skipping to change at page 8, line 24 skipping to change at page 8, line 30
then add the current set of A and/or AAAA RRs, if any, for the then add the current set of A and/or AAAA RRs, if any, for the
client. client.
If the UPDATE request succeeds, the updater can conclude that the If the UPDATE request succeeds, the updater can conclude that the
current client was the last client associated with the FQDN, and that current client was the last client associated with the FQDN, and that
the FQDN now contains the updated A and/or AAAA RRs. The update is the FQDN now contains the updated A and/or AAAA RRs. The update is
now complete (and a client updater is finished, while a server would now complete (and a client updater is finished, while a server would
then proceed to perform a PTR RR update). then proceed to perform a PTR RR update).
If the response to the UPDATE request returns NXDOMAIN, the FQDN is If the response to the UPDATE request returns NXDOMAIN, the FQDN is
no longer in use and the updater proceeds back to Section 5.3.1. no longer in use, and the updater proceeds back to Section 5.3.1.
If the response to the UPDATE request returns NXRRSET, there are two If the response to the UPDATE request returns NXRRSET, there are two
possibilities - there are no DHCID RRs for the FQDN or the DHCID RR possibilities: there are no DHCID RRs for the FQDN, or the DHCID RR
does not match. In either case, the updater proceeds to does not match. In either case, the updater proceeds to
Section 5.3.3. Section 5.3.3.
5.3.3. FQDN in Use by another Client 5.3.3. FQDN in Use by Another Client
As the FQDN appears to be in use by another client or is not As the FQDN appears to be in use by another client or is not
associated with any client, the updater SHOULD either choose another associated with any client, the updater SHOULD either choose another
FQDN and restart the update process with this new FQDN or terminate FQDN and restart the update process with this new FQDN or terminate
the update with a failure. the update with a failure.
Techniques that may be considered to disambiguate FQDNs include Techniques that may be considered to disambiguate FQDNs include
adding some suffix or prefix to the hostname portion of the FQDN or adding some suffix or prefix to the hostname portion of the FQDN or
randomly generating a hostname. randomly generating a hostname.
5.4. Adding PTR RR Entries to DNS 5.4. Adding PTR RR Entries to DNS
The DHCP server submits a DNS UPDATE request that deletes all of the The DHCP server submits a DNS UPDATE request that deletes all of the
PTR RRs associated with the client's assigned IP address, and adds a PTR RRs associated with the client's assigned IP address and adds a
PTR RR whose data is the client's (possibly disambiguated) FQDN. The PTR RR whose data is the client's (possibly disambiguated) FQDN. The
server MAY also add a DHCID RR as specified in Section 4, in which server MAY also add a DHCID RR as specified in Section 4, in which
case it would include a delete of all of the DHCID RRs associated case it would include a delete of all of the DHCID RRs associated
with the client's assigned IP address, and adds a DHCID RR for the with the client's assigned IP address and would add a DHCID RR for
client. the client.
There is no need to validate the DHCID RR for PTR updates as the DHCP There is no need to validate the DHCID RR for PTR updates as the DHCP
server (or servers) only assigns an address to a single client at a server (or servers) only assigns an address to a single client at a
time. time.
5.5. Removing Entries from DNS 5.5. Removing Entries from DNS
The most important consideration in removing DNS entries is to be The most important consideration in removing DNS entries is to be
sure that an entity removing a DNS entry is only removing an entry sure that an entity removing a DNS entry is only removing an entry
that it added, or for which an administrator has explicitly assigned that it added, or for which an administrator has explicitly assigned
skipping to change at page 9, line 35 skipping to change at page 9, line 41
However, the updater should only remove the DHCID RR if there are no However, the updater should only remove the DHCID RR if there are no
A or AAAA RRs remaining for the client. A or AAAA RRs remaining for the client.
In order to perform this A or AAAA RR delete, the updater prepares an In order to perform this A or AAAA RR delete, the updater prepares an
UPDATE request that contains a prerequisite that asserts that the UPDATE request that contains a prerequisite that asserts that the
DHCID RR exists whose data is the client identity described in DHCID RR exists whose data is the client identity described in
Section 4 and contains an update section that deletes the client's Section 4 and contains an update section that deletes the client's
specific A or AAAA RR. specific A or AAAA RR.
If the UPDATE request succeeds, the updater prepares a second UPDATE If the UPDATE request succeeds, the updater prepares a second UPDATE
request that contains three prerequisites and contains an update request that contains three prerequisites and an update section that
section that deletes all RRs for the FQDN. The first prerequisite deletes all RRs for the FQDN. The first prerequisite asserts that
asserts that the DHCID RR exists whose data is the client identity the DHCID RR exists whose data is the client identity described in
described in Section 4. The second prerequisite asserts that there Section 4. The second prerequisite asserts that there are no A RRs.
are no A RRs. The third prerequisite asserts that there are no AAAA The third prerequisite asserts that there are no AAAA RRs.
RRs.
If either request fails, the updater MUST NOT delete the FQDN. It If either request fails, the updater MUST NOT delete the FQDN. It
may be that the client whose address has expired has moved to another may be that the client whose address has expired has moved to another
network and obtained an address from a different server, which has network and obtained an address from a different server, which has
caused the client's A or AAAA RR to be replaced. Or, the DNS data caused the client's A or AAAA RR to be replaced. Or, the DNS data
may have been removed or altered by an administrator. may have been removed or altered by an administrator.
5.6. Updating Other RRs 5.6. Updating Other RRs
The procedures described in this document only cover updates to the The procedures described in this document only cover updates to the
A, AAAA, PTR, and DHCID RRs. Updating other types of RRs is outside A, AAAA, PTR, and DHCID RRs. Updating other types of RRs is outside
the scope of this document. the scope of this document.
6. Security Considerations 6. Security Considerations
Administrators should be wary of permitting unsecured DNS updates to Administrators should be wary of permitting unsecured DNS updates to
zones, whether or not they are exposed to the global Internet. Both zones, whether or not they are exposed to the global Internet. Both
DHCP clients and servers SHOULD use some form of update request DHCP clients and servers SHOULD use some form of update request
authentication (e.g., TSIG [13]) when performing DNS updates. authentication (e.g., TSIG [13]) when performing DNS updates.
Whether a DHCP client may be responsible for updating an FQDN to IP Whether a DHCP client may be 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 may be based on the security model that is used with the alternatives may be based on the security model that is used with the
Dynamic DNS Update protocol (e.g., only a client may have sufficient Dynamic 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).
Whether a DHCP server is always responsible for updating the FQDN to Whether a DHCP server is always responsible for updating the FQDN-
IP address mapping (in addition to updating the IP to FQDN mapping), to-IP-address mapping (in addition to updating the IP-to-FQDN
regardless of the wishes of an individual DHCP client, is also a mapping), regardless of the wishes of an individual DHCP client, is
site-local matter. The choice between the two alternatives may be also a site-local matter. The choice between the two alternatives
based on the security model that is being used with dynamic DNS may be based on the security model that is being used with dynamic
updates. In cases where a DHCP server is performing DNS updates on DNS updates. In cases where a DHCP server is performing DNS updates
behalf of a client, the DHCP server should be sure of the FQDN to use on behalf of a client, the DHCP server should be sure of the FQDN to
for the client, and of the identity of the client. use for the 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 their clients, given the absence of confidence in the identities of their 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 FQDN to use for a client, but ways for a DHCP server to develop an FQDN to use for a client, but
only in certain relatively rare circumstances will the DHCP server only in certain relatively rare circumstances will the DHCP server
know for certain the identity of the client. If [14] becomes widely know for certain the identity of the client. If [14] becomes widely
deployed this may become more customary. deployed, this may become more customary.
One example of a situation that offers some extra assurances is when One example of a situation that offers some extra assurances is when
the DHCP client is connected to a network through a DOCSIS cable the DHCP client is connected to a network through a DOCSIS cable
modem, and the Cable Modem Termination System (head-end) of the cable modem, and the Cable Modem Termination System (head-end) of the cable
modem ensures that MAC address spoofing simply does not occur. modem ensures that MAC address spoofing simply does not occur.
Another example of a configuration that might be trusted is when Another example of a configuration that might be trusted is when
clients obtain network access via a network access server using PPP. clients obtain network access via a network access server using PPP.
The Network Access Server (NAS) itself might be obtaining IP The Network Access Server (NAS) itself might be obtaining IP
addresses via DHCP, encoding client identification into the DHCP addresses via DHCP, encoding client identification into the DHCP
client-id option. In this case, the NAS as well as the DHCP server client-id option. In this case, the NAS as well as the DHCP server
skipping to change at page 11, line 21 skipping to change at page 11, line 24
Lewis, Michael Lewis, Josh Littlefield, Michael Patton, Pekka Savola, Lewis, Michael Lewis, Josh Littlefield, Michael Patton, Pekka Savola,
and Glenn Stump for their review and comments. and Glenn Stump for their review and comments.
8. References 8. References
8.1. Normative References 8.1. 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] Stapp, M., Gustafsson, A., and T. Lemon, "A DNS RR for Encoding [2] Stapp, M., Lemon, T., and A. Gustafsson, "A DNS Resource Record
DHCP Information (draft-ietf-dnsext-dhcid-rr-*)", February 2006. (RR) for Encoding Dynamic Host Configuration Protocol (DHCP)
Information (DHCID RR), RFC 4701, October 2006.
[3] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic [3] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic
Updates in the Domain Name System (DNS UPDATE)", RFC 2136, Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
April 1997. April 1997.
[4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, [4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. [5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003. RFC 3315, July 2003.
8.2. Informative References 8.2. Informative References
[6] Mockapetris, P., "Domain names - implementation and [6] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[7] Malkin, G., "Internet Users' Glossary", RFC 1983, August 1996. [7] Malkin, G., "Internet Users' Glossary", FYI 18, RFC 1983,
August 1996.
[8] Stapp, M. and Y. Rekhter, "The DHCP Client FQDN Option [8] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host
(draft-ietf-dhc-fqdn-option-*.txt)", February 2006. Configuration Protocol (DHCP) Client Fully Qualified Domain
Name (FQDN) Option", RFC 4702, October 2006.
[9] Volz, B., "The DHCPv6 Client FQDN Option [9] Volz, B., "The Dynamic Host Configuration Protocol for IPv6
(draft-ietf-dhc-dhcpv6-fqdn-*.txt)", February 2006. (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option", RFC
4704, October 2006.
[10] Wellington, B., "Secure Domain Name System (DNS) Dynamic [10] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000. Update", RFC 3007, November 2000.
[11] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers [11] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers
for Dynamic Host Configuration Protocol Version Four (DHCPv4)", for Dynamic Host Configuration Protocol Version Four (DHCPv4)",
RFC 4361, February 2006. RFC 4361, February 2006.
[12] 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.
skipping to change at page 13, line 14 skipping to change at page 12, line 35
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
Phone: 978.936.1535 Phone: 978.936.1535
Email: mjs@cisco.com EMail: mjs@cisco.com
Bernie Volz Bernie Volz
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Phone: 978.936.0382 Phone: 978.936.0382
Email: volz@cisco.com EMail: volz@cisco.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 14, line 29 skipping to change at page 13, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity Acknowledgement
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
 End of changes. 50 change blocks. 
137 lines changed or deleted 125 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/