Network Working Group M. Stapp
Request for Comments: 4703 B. Volz
Category: Standards Track Cisco Systems, Inc.
October 2006
Network Working Group M. Stapp
Request for Comments: 4703 B. Volz
Category: Standards Track Cisco Systems, Inc.
October 2006
Resolution of Fully Qualified Domain Name (FQDN) Conflicts among Dynamic Host Configuration Protocol (DHCP) Clients
解决动态主机配置协议（DHCP）客户端之间的完全限定域名（FQDN）冲突
Status of This Memo
关于下段备忘
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.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2006).
版权所有（C）互联网协会（2006年）。
Abstract
摘要
The Dynamic Host Configuration Protocol (DHCP) provides a mechanism for host configuration that includes dynamic assignment of IP addresses and fully qualified domain names. To maintain accurate name-to-IP-address and IP-address-to-name mappings in the DNS, these dynamically assigned addresses and fully qualified domain names (FQDNs) require updates to the DNS. This document identifies situations in which conflicts in the use of fully qualified domain 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.
动态主机配置协议（DHCP）提供了一种主机配置机制，包括动态分配IP地址和完全限定的域名。为了在DNS中保持准确的名称到IP地址和IP地址到名称的映射，这些动态分配的地址和完全限定的域名（FQDN）需要更新DNS。本文档确定了DHCP客户端和服务器之间可能出现完全限定域名使用冲突的情况，并描述了在解决这些冲突时使用DHCID DNS资源记录（RR）的策略。
Table of Contents
目录
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Issues with DNS Update in DHCP Environments .....................4
3.1. Client Misconfiguration ....................................4
3.2. Multiple DHCP Servers ......................................5
4. Use of the DHCID RR .............................................5
5. Procedures for Performing DNS Updates ...........................6
5.1. Error Return Codes .........................................6
5.2. Dual IPv4/IPv6 Client Considerations .......................6
5.3. Adding A and/or AAAA RRs to DNS ............................7
5.3.1. Initial DHCID RR Request ............................7
5.3.2. DNS UPDATE When FQDN in Use .........................7
5.3.3. FQDN in Use by Another Client .......................8
5.4. Adding PTR RR Entries to DNS ...............................8
5.5. Removing Entries from DNS ..................................9
5.6. Updating Other RRs ........................................10
6. Security Considerations ........................................10
7. Acknowledgements ...............................................11
8. References .....................................................11
8.1. Normative References ......................................11
8.2. Informative References ....................................11
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Issues with DNS Update in DHCP Environments .....................4
3.1. Client Misconfiguration ....................................4
3.2. Multiple DHCP Servers ......................................5
4. Use of the DHCID RR .............................................5
5. Procedures for Performing DNS Updates ...........................6
5.1. Error Return Codes .........................................6
5.2. Dual IPv4/IPv6 Client Considerations .......................6
5.3. Adding A and/or AAAA RRs to DNS ............................7
5.3.1. Initial DHCID RR Request ............................7
5.3.2. DNS UPDATE When FQDN in Use .........................7
5.3.3. FQDN in Use by Another Client .......................8
5.4. Adding PTR RR Entries to DNS ...............................8
5.5. Removing Entries from DNS ..................................9
5.6. Updating Other RRs ........................................10
6. Security Considerations ........................................10
7. Acknowledgements ...............................................11
8. References .....................................................11
8.1. Normative References ......................................11
8.2. Informative References ....................................11
"The Client FQDN Option" [8] includes a description of the operation of [4] clients and servers that use the DHCPv4 client FQDN option. "The DHCPv6 Client FQDN Option" [9] includes a description of the operation of [5] clients and servers that use the DHCPv6 client FQDN option. Through the use of the client FQDN option, DHCP clients and servers can negotiate the client's FQDN and the allocation of responsibility for updating the DHCP client's A and/or AAAA RRs. This document identifies situations in which conflicts in the use of FQDNs may arise among DHCP clients and servers, and it describes a strategy for the use of the DHCID DNS resource record [2] in resolving those conflicts.
“客户端FQDN选项”[8]包括使用DHCPv4客户端FQDN选项的[4]客户端和服务器的操作说明。“DHCPv6客户端FQDN选项”[9]包括使用DHCPv6客户端FQDN选项的[5]个客户端和服务器的操作说明。通过使用客户端FQDN选项，DHCP客户端和服务器可以协商客户端的FQDN以及更新DHCP客户端A和/或AAAA RRs的责任分配。本文档确定了DHCP客户端和服务器之间可能出现FQDN使用冲突的情况，并描述了在解决这些冲突时使用DHCID DNS资源记录[2]的策略。
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 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 that allow the client to modify its own FQDN. 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 that initiate DNS updates.
在任何情况下，站点是否允许所有、部分或不允许DHCP服务器和客户端对其控制的区域执行DNS更新（[3]、[10]），完全取决于本地管理策略。本文件不要求任何具体的行政政策，也不提出任何具体的行政政策。可能的策略范围非常广泛，从仅为DHCP服务器提供DNS服务器将接受的凭据的站点，到为每个单独的DHCP客户端配置了允许客户端修改其自己的FQDN的凭据的站点。兼容实现可能支持部分或全部这些可能性。此外，本规范仅适用于DHCP客户端和服务器进程；它不适用于启动DNS更新的其他进程。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [1].
本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照[1]中所述进行解释。
This document assumes familiarity with DNS terminology defined in [6] and DHCP terminology defined in [4] and [5].
本文档假设您熟悉[6]中定义的DNS术语以及[4]和[5]中定义的DHCP术语。
FQDN, or Fully Qualified Domain Name, is the full name of a system, rather than just its hostname. For example, "venera" is a hostname, and "venera.isi.edu" is an FQDN. See [7].
FQDN或完全限定域名是系统的全名，而不仅仅是主机名。例如，“venera”是主机名，“venera.isi.edu”是FQDN。见[7]。
DOCSIS, or Data-Over-Cable Service Interface Specifications, is defined by CableLabs.
DOCSIS或有线数据服务接口规范由CableLabs定义。
There are two DNS update situations that require special consideration in DHCP environments: cases where more than one DHCP client has been configured with the same FQDN, and cases where more 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 modified in inconsistent ways unless the updaters have a mechanism that allows them to detect anomalous situations. If DNS updaters can detect these situations, site administrators can configure the updaters' behavior so that the site's policies can be enforced. This specification describes a mechanism designed to allow updaters to detect these situations and suggests that DHCP implementations use this mechanism by default.
在DHCP环境中，有两种DNS更新情况需要特别考虑：多个DHCP客户端配置了相同FQDN的情况，以及多个DHCP服务器被授予在区域中执行DNS更新的权限的情况。在这些情况下，DNS记录有可能以不一致的方式被修改，除非更新程序有一种机制允许它们检测异常情况。如果DNS更新程序可以检测到这些情况，则站点管理员可以配置更新程序的行为，以便可以强制执行站点的策略。本规范描述了一种允许更新程序检测这些情况的机制，并建议DHCP实现默认使用这种机制。
Administrators may wish to maintain a one-to-one relationship between active DHCP clients and FQDNs, and to maintain consistency between a client's A, AAAA, and PTR RRs. Clients that are not represented in the DNS, or clients that inadvertently share an FQDN with another client may encounter inconsistent behavior or may not be able to obtain access to network resources. Whether each DHCP client is configured with an FQDN by its administrator or whether the DHCP server is configured to distribute the clients' FQDN, the consistency of the DNS data is entirely dependent on the accuracy of the configuration procedure. Sites that deploy [10] may configure credentials for each client and its assigned FQDN in a way that is more error-resistant, as both the FQDN and credentials must match.
管理员可能希望在活动DHCP客户端和FQDN之间保持一对一的关系，并在客户端的a、AAAA和PTR RRs之间保持一致性。DNS中未表示的客户端，或无意中与其他客户端共享FQDN的客户端可能会遇到不一致的行为或无法访问网络资源。无论每个DHCP客户端是由其管理员配置FQDN，还是DHCP服务器配置为分发客户端的FQDN，DNS数据的一致性完全取决于配置过程的准确性。部署[10]的站点可以为每个客户端及其分配的FQDN配置更具容错性的凭据，因为FQDN和凭据必须匹配。
Consider an example in which two DHCP clients in the "example.com" network are both configured with the hostname "foo". The clients are 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 its DHCP server adds a PTR RR corresponding to its assigned IP address. When the second client, client B, boots, it is also configured via DHCP, and it also begins to update "foo.example.com".
考虑一个例子，其中“示例.com”网络中的两个DHCP客户端都配置了主机名“FO”。允许客户端执行自己的DNS更新。第一个客户端，客户端A，通过DHCP配置。它向“foo.example.com”添加一个RR，其DHCP服务器添加一个与其分配的IP地址相对应的PTR RR。当第二个客户端B引导时，它也通过DHCP进行配置，并开始更新“foo.example.com”。
At this point, the "example.com" administrators may wish to establish some policy about DHCP clients' FQDNs. If the policy is that each client that boots should replace any existing A RR that matches its FQDN, Client B can proceed, though Client A may encounter problems. In this example, Client B replaces the A RR associated with "foo.example.com". Client A must have some way to recognize that the RR associated with "foo.example.com" now contains information for Client B, so that it can avoid modifying the RR. When Client A's assigned IP address expires, for example, it should not remove an RR that reflects Client B's DHCP-assigned IP address.
此时，“example.com”管理员可能希望建立一些有关DHCP客户端FQDN的策略。如果策略是每个引导的客户端都应该替换与其FQDN匹配的任何现有A RR，则客户端B可以继续，尽管客户端A可能会遇到问题。在本例中，客户端B替换与“foo.example.com”关联的A RR。客户机A必须有某种方式来识别与“foo.example.com”关联的RR现在包含客户机B的信息，以便它可以避免修改RR。例如，当客户端A的分配IP地址过期时，它不应删除反映客户端B的DHCP分配IP地址的RR。
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 able to determine if it is not the client associated with "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 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 either retain persistent state about the last IP address it was 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" in order to implement the site's policy.
如果策略是具有给定FQDN的第一个DHCP客户端应该是与该FQDN关联的唯一客户端，则客户端B需要能够确定它是否不是与“foo.example.com”关联的客户端。可能是客户端A首先启动，客户端B应该选择另一个FQDN。也可能是B在新的子网上启动并接收到新的IP地址分配，在这种情况下，B应使用其新的IP地址更新DNS。它必须保留最后分配的IP地址的持久状态（除了当前IP地址之外），或者必须有其他方法来检测它是“foo.example.com”的最后一个更新程序，以便实现站点的策略。
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 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 an FQDN to a client. Such a database is necessarily proprietary, however, and the approach does not work once more than one DHCP server is deployed.
可以安排DHCP服务器代表其客户端执行和/或AAAA RR更新。若一个DHCP服务器管理一个站点上的所有DHCP客户端，它可以维护一个正在使用的FQDN数据库，并可以在将FQDN分配给客户端之前检查该数据库。然而，这样的数据库必须是专有的，并且一旦部署了多个DHCP服务器，这种方法就不起作用。
When multiple DHCP servers are deployed, the servers require a way to coordinate the identities of DHCP clients. Consider an example in which DHCPv4 Client A boots, obtains an IP address from Server S1, presenting the hostname "foo" in a Client FQDN option [8] in its DHCPREQUEST message. Server S1 updates the FQDN "foo.example.com", 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 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 address to the FQDN "foo.example.com". At this point, without some 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 know whether Client A is currently associated with the FQDN, or whether A is a different client configured with the same FQDN. If the servers cannot distinguish between these situations, they cannot enforce the site's naming policies.
部署多个DHCP服务器时，服务器需要一种协调DHCP客户端身份的方法。考虑一个示例，其中DHCPv4客户端A引导，从服务器S1获得IP地址，在其DHCPRQuestE消息中在客户端FQDN选项（8）中显示主机名“FoO”。服务器S1更新FQDN“foo.example.com”，添加一个包含分配给A的IP地址的RR。然后，客户端移动到另一个子网，由服务器S2提供服务。当客户端A在新子网上引导时，服务器S2将为其分配一个新的IP地址，并将尝试向FQDN“foo.example.com”添加一个包含新分配的IP地址的RR。此时，如果S2无法使用某些通信机制询问S1（以及更新该区域的所有其他DHCP服务器）有关客户端的信息，S2将无法知道客户端A当前是否与FQDN关联，或者A是否是配置了相同FQDN的其他客户端。如果服务器无法区分这些情况，则无法强制执行站点的命名策略。
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 been associated with an FQDN, in order to offer administrators the opportunity to configure updater behavior.
这两个问题的解决方案是更新程序（DHCP客户端或DHCP服务器）能够确定哪个DHCP客户端与FQDN关联，以便为管理员提供配置更新程序行为的机会。
For this purpose, a DHCID RR, specified in [2], is used to associate client identification information with an FQDN and the A, AAAA, and 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 specifies a unique client identity, based on data from the client's DHCP message. In this model, only one client is associated with a given FQDN at a time.
为此，使用[2]中指定的DHCID RR将客户端标识信息与FQDN以及与该FQDN关联的a、AAAA和PTR RR关联。当客户机或服务器为客户机添加、AAAA或PTR RRs时，它还会根据客户机DHCP消息中的数据添加指定唯一客户机标识的DHCID RR。在此模型中，一次只有一个客户端与给定的FQDN关联。
By associating this ownership information with each FQDN, cooperating DNS updaters may determine whether their client is currently associated with a particular FQDN and implement the appropriately configured administrative policy. In addition, DHCP clients that currently have FQDNs may move from one DHCP server to another without losing their FQDNs.
通过将此所有权信息与每个FQDN关联，协作DNS更新程序可以确定其客户端当前是否与特定FQDN关联，并实施适当配置的管理策略。此外，当前具有FQDN的DHCP客户端可以在不丢失其FQDN的情况下从一个DHCP服务器移动到另一个DHCP服务器。
The specific algorithm utilizing the DHCID RR to signal client ownership is explained below. The algorithm only works in the case where the updating entities all cooperate -- this approach is advisory only and is not a substitute for DNS security, nor is it replaced by DNS security.
下面解释使用dhcidrr来表示客户端所有权的特定算法。该算法只在更新实体都合作的情况下工作——这种方法只是建议性的，不能替代DNS安全性，也不能被DNS安全性取代。
Certain RCODEs defined in [3] indicate that the destination DNS server cannot perform an update, i.e., FORMERR, SERVFAIL, REFUSED, NOTIMP. If one of these RCODEs is returned, the updater MUST terminate its update attempt. Other RCODEs [13] may indicate that there are problems with the key being used and may mean to try a different key, if available, or to terminate the operation. Because some errors may indicate a misconfiguration of the updater or the DNS server, the updater MAY attempt to signal to its administrator that an error has occurred, e.g., through a log message.
[3]中定义的某些RCODE表示目标DNS服务器无法执行更新，即FORMERR、SERVFAIL、REQUEED、NOTIMP。如果返回其中一个RCODE，则更新程序必须终止其更新尝试。其他RCODE[13]可能表明所使用的密钥存在问题，可能意味着尝试其他密钥（如果可用）或终止操作。由于某些错误可能表示更新程序或DNS服务器配置错误，因此更新程序可能会尝试向其管理员发出发生错误的信号，例如，通过日志消息。
At the time of publication of this document, a small minority of DHCP clients support both IPv4 and IPv6. We anticipate, however, that a transition will take place over a period of time, and more sites will have dual-stack clients present. IPv6 clients require updates of AAAA RRs; IPv4 client require updates of A RRs. The administrators of mixed deployments will likely wish to permit a single FQDN to contain A and AAAA RRs from the same client.
在本文档发布时，少数DHCP客户端同时支持IPv4和IPv6。然而，我们预计过渡将在一段时间内发生，更多的站点将有双堆栈客户端。IPv6客户端要求更新AAAA RRs；IPv4客户端要求更新RRs。混合部署的管理员可能希望允许单个FQDN包含来自同一客户端的a和AAAA RRs。
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 the DHCP Unique Identifier (DUID) for DHCPv4 client identifiers such
希望允许单个FQDN同时包含a和AAAA RRs的站点必须使用支持使用DHCP唯一标识符（DUID）作为DHCPv4客户端标识符的DHCPv4客户端和服务器，如
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 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 under a single FQDN because of the DHCID RR conflicts that result.
该DUID用于通过DHCPv4和DHCPv6为客户端计算DHCID RR的RDATA；见[11]。否则，使用老式DHCPv4客户端标识符（请参见[4]和[12]）的双堆栈客户端将只能在单个FQDN下的DNS中具有其a或AAAA记录，因为会导致DHCID RR冲突。
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.
当DHCP客户端或服务器打算更新和/或AAAA RRs时，将从第5.3.1节中的更新请求开始。
As the update sequence below can result in loops, implementers SHOULD limit the total number of attempts for a single transaction.
由于下面的更新序列可能导致循环，实现者应该限制单个事务的尝试总数。
The updater prepares a DNS UPDATE request that includes as a prerequisite the assertion that the FQDN does not exist. The update section of the request attempts to add the new FQDN and its IP address mapping (A and/or AAAA RRs) and the DHCID RR with its unique client identity.
更新程序准备一个DNS更新请求，该请求包含FQDN不存在的断言作为先决条件。请求的更新部分尝试添加新FQDN及其IP地址映射（A和/或AAAA RRs）以及具有唯一客户端标识的DHCID RR。
If the UPDATE request succeeds, the A and/or AAAA RR update is now complete (and a client updater is finished, while a server would then proceed to perform a PTR RR update).
如果更新请求成功，A和/或AAAA RR更新现在完成（客户端更新程序完成，而服务器将继续执行PTR RR更新）。
If the response to the UPDATE returns YXDOMAIN, the updater can now conclude that the intended FQDN is in use and proceeds to Section 5.3.2.
如果对更新的响应返回YXDOMAIN，则更新程序现在可以得出预期FQDN正在使用的结论，并转至第5.3.2节。
If any other status is returned, the updater SHOULD NOT attempt an update (see Section 5.1).
如果返回任何其他状态，则更新程序不应尝试更新（请参阅第5.1节）。
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 are two prerequisites. The first prerequisite is that the FQDN exists. The second is that the desired FQDN has attached to it a DHCID RR whose contents match the client identity. The update section of the UPDATE request contains:
更新程序接下来尝试通过准备更新请求（其中有两个先决条件）来确认FQDN未被其他客户机使用。第一个先决条件是FQDN存在。第二个问题是，所需的FQDN附加了一个DHCID RR，其内容与客户机标识匹配。更新请求的更新部分包含：
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 the FQDN, or if this update is adding an A and the updater only desires a single IP address on the FQDN.
1. 如果这是A更新或AAAA更新且更新程序不需要FQDN上的A记录，或者如果此更新正在添加A且更新程序只需要FQDN上的单个IP地址，则删除FQDN上的任何现有A RRs。
2. A delete of the existing AAAA RRs on the FQDN if the updater does not desire AAAA records on the FQDN, or if this update is adding an AAAA and the updater only desires a single IP address on the FQDN.
2. 如果更新程序不需要FQDN上的AAAA记录，或者如果此更新正在添加AAAA且更新程序只需要FQDN上的单个IP地址，则删除FQDN上现有的AAAA RRs。
3. An add (or adds) of the A RR that matches the DHCP binding if this is an A update.
3. 若这是一个更新，则添加和DHCP绑定匹配的RR。
4. Adds of the AAAA RRs that match the DHCP bindings if this is an AAAA update.
4. 如果这是AAAA更新，则添加与DHCP绑定匹配的AAAA RRs。
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 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 then add the current set of A and/or AAAA RRs, if any, for the client.
是否删除A或AAAA RRs取决于更新程序或更新程序的策略。例如，如果更新程序是客户端或配置为客户端所在链接的唯一DHCP服务器，则更新程序可能会发现删除所有A和/或AAAA RRs，然后为客户端添加当前A和/或AAAA RRs集（如果有）是有益的。
If the UPDATE request succeeds, the updater can conclude that the 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 now complete (and a client updater is finished, while a server would then proceed to perform a PTR RR update).
如果更新请求成功，更新程序可以断定当前客户端是与FQDN关联的最后一个客户端，并且FQDN现在包含更新的A和/或AAAA RRs。更新现在已完成（客户端更新程序已完成，而服务器将继续执行PTR更新）。
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.
如果对更新请求的响应返回NXDOMAIN，则FQDN不再使用，更新程序将返回第5.3.1节。
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 does not match. In either case, the updater proceeds to Section 5.3.3.
如果对更新请求的响应返回NXRRSET，则有两种可能性：FQDN没有DHCID RRs，或者DHCID RR不匹配。在任何一种情况下，更新程序都会转到第5.3.3节。
As the FQDN appears to be in use by another client or is not associated with any client, the updater SHOULD either choose another FQDN and restart the update process with this new FQDN or terminate the update with a failure.
由于FQDN似乎正在被其他客户端使用或与任何客户端都没有关联，更新程序应该选择另一个FQDN并使用此新FQDN重新启动更新过程，或者在更新失败时终止更新。
Techniques that may be considered to disambiguate FQDNs include adding some suffix or prefix to the hostname portion of the FQDN or randomly generating a hostname.
可以考虑消除FQDN歧义的技术包括向FQDN的主机名部分添加一些后缀或前缀，或随机生成主机名。
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 RR whose data is the client's (possibly disambiguated) FQDN. The
DHCP服务器提交一个DNS更新请求，该请求删除与客户端分配的IP地址相关联的所有PTR RR，并添加一个PTR RR，其数据为客户端的（可能消除歧义的）FQDN。这个
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 with the client's assigned IP address and would add a DHCID RR for the client.
服务器还可以按照第4节的规定添加DHCID RR，在这种情况下，它将包括删除与客户端分配的IP地址相关联的所有DHCID RR，并为客户端添加DHCID RR。
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 time.
无需为PTR更新验证DHCID RR，因为DHCP服务器一次只为单个客户端分配一个地址。
The most important consideration in removing DNS entries is to be sure that an entity removing a DNS entry is only removing an entry that it added, or for which an administrator has explicitly assigned it responsibility.
删除DNS条目时最重要的考虑事项是确保删除DNS条目的实体仅删除其添加的条目，或管理员已明确指定其责任的条目。
When an address' lease time or valid lifetime expires or a DHCP client issues a DHCPRELEASE [4] or Release [5] request, the DHCP server SHOULD delete the PTR RR that matches the DHCP binding, if one was successfully added. The server's UPDATE request SHOULD assert that the domain name (PTRDNAME field) in the PTR record matches the FQDN of the client whose address has expired or been released and should delete all RRs for the FQDN.
当地址的租约时间或有效生存期到期，或者DHCP客户端发出DHCPRELEASE[4]或Release[5]请求时，DHCP服务器应删除与DHCP绑定匹配的PTR RR（如果已成功添加）。服务器的更新请求应声明PTR记录中的域名（ptrName字段）与地址已过期或已释放的客户端的FQDN匹配，并应删除FQDN的所有RRs。
The entity chosen to handle the A or AAAA records for this client (either the client or the server) SHOULD delete the A or AAAA records that were added when the address was assigned to the client. However, the updater should only remove the DHCID RR if there are no A or AAAA RRs remaining for the client.
选择用于处理此客户端（客户端或服务器）的A或AAAA记录的实体应删除在将地址分配给客户端时添加的A或AAAA记录。但是，只有当客户端没有剩余的A或AAAA RRs时，更新程序才应该删除DHCID RR。
In order to perform this A or AAAA RR delete, the updater prepares an UPDATE request that contains a prerequisite that asserts that the DHCID RR exists whose data is the client identity described in Section 4 and contains an update section that deletes the client's specific A or AAAA RR.
为了执行此A或AAAA RR删除，更新程序准备一个更新请求，其中包含一个先决条件，该先决条件断言DHCID RR存在，其数据为第4节中描述的客户端标识，并包含一个删除客户端特定A或AAAA RR的更新节。
If the UPDATE request succeeds, the updater prepares a second UPDATE request that contains three prerequisites and an update section that deletes all RRs for the FQDN. The first prerequisite asserts that the DHCID RR exists whose data is the client identity described in Section 4. The second prerequisite asserts that there are no A RRs. The third prerequisite asserts that there are no AAAA RRs.
如果更新请求成功，更新程序将准备第二个更新请求，其中包含三个先决条件和一个更新节，该更新节删除FQDN的所有RRs。第一个先决条件断言存在DHCID RR，其数据是第4节中描述的客户机标识。第二个先决条件断言不存在RRs。第三个先决条件声称不存在AAAA RRs。
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 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 may have been removed or altered by an administrator.
如果任一请求失败，更新程序不得删除FQDN。可能是地址已过期的客户端已移动到另一个网络，并从不同的服务器获取了地址，这导致客户端的a或AAAA RR被替换。或者，DNS数据可能已被管理员删除或更改。
The procedures described in this document only cover updates to the A, AAAA, PTR, and DHCID RRs. Updating other types of RRs is outside the scope of this document.
本文档中描述的程序仅涵盖A、AAAA、PTR和DHCID RRs的更新。更新其他类型的RRs不在本文件范围内。
Administrators should be wary of permitting unsecured DNS updates to zones, whether or not they are exposed to the global Internet. Both DHCP clients and servers SHOULD use some form of update request authentication (e.g., TSIG [13]) when performing DNS updates.
管理员应警惕允许对区域进行不安全的DNS更新，无论它们是否暴露于全球互联网。在执行DNS更新时，DHCP客户端和服务器都应该使用某种形式的更新请求身份验证（例如，TSIG[13]）。
Whether a DHCP client may be responsible for updating an FQDN-to-IP-address mapping, or whether this is the responsibility of the DHCP server, is a site-local matter. The choice between the two 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 credentials to perform updates to the FQDN-to-IP-address mapping for its FQDN).
DHCP客户端是否负责更新FQDN到IP地址的映射，或者这是否是DHCP服务器的责任，这是站点本地的问题。这两个备选方案之间的选择可能基于与动态DNS更新协议一起使用的安全模型（例如，只有客户端可能具有足够的凭据来执行对其FQDN的FQDN到IP地址映射的更新）。
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 an individual DHCP client, is also a site-local matter. The choice between the two alternatives may be based on the security model that is being used with dynamic DNS updates. In cases where a DHCP server is performing DNS updates on behalf of a client, the DHCP server should be sure of the FQDN to use for the client, and of the identity of the client.
DHCP服务器是否总是负责更新FQDN到IP地址的映射（除了更新IP到FQDN的映射之外），而不管单个DHCP客户端的意愿如何，这也是站点本地的问题。这两个备选方案之间的选择可能基于与动态DNS更新一起使用的安全模型。在DHCP服务器代表客户端执行DNS更新的情况下，DHCP服务器应确保用于客户端的FQDN以及客户端的标识。
Currently, it is difficult for DHCP servers to develop much confidence in the identities of their clients, given the absence of entity authentication from the DHCP protocol itself. There are many 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 know for certain the identity of the client. If [14] becomes widely deployed, this may become more customary.
目前，由于DHCP协议本身没有实体身份验证，DHCP服务器很难对其客户端的身份建立信心。DHCP服务器有许多方法来开发用于客户端的FQDN，但只有在某些相对罕见的情况下，DHCP服务器才能确定客户端的身份。如果[14]得到广泛部署，这可能会变得更为常见。
One example of a situation that offers some extra assurances is when 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 ensures that MAC address spoofing simply does not occur. Another example of a configuration that might be trusted is when clients obtain network access via a network access server using PPP. The Network Access Server (NAS) itself might be obtaining IP addresses via DHCP, encoding client identification into the DHCP client-id option. In this case, the NAS as well as the DHCP server might be operating within a trusted environment, in which case the
提供一些额外保证的情况的一个示例是，DHCP客户端通过DOCSIS电缆调制解调器连接到网络，并且电缆调制解调器的电缆调制解调器终端系统（前端）确保不会发生MAC地址欺骗。另一个可能受信任的配置示例是当客户端使用PPP通过网络访问服务器获得网络访问时。网络访问服务器（NAS）本身可能通过DHCP获取IP地址，将客户端标识编码到DHCP客户端id选项中。在这种情况下，NAS和DHCP服务器可能在受信任的环境中运行，在这种情况下
DHCP server could be configured to trust that the user authentication and authorization processing of the NAS was sufficient, and would therefore trust the client identification encoded within the DHCP client-id.
DHCP服务器可以配置为信任NAS的用户身份验证和授权处理足够，因此将信任DHCP client-id中编码的客户端标识。
Many thanks to Mark Beyer, Jim Bound, Ralph Droms, Robert Elz, Peter Ford, Olafur Gudmundsson, Edie Gunter, Andreas Gustafsson, David W. Hankins, R. Barr Hibbs, Kim Kinnear, Stuart Kwan, Ted Lemon, Ed Lewis, Michael Lewis, Josh Littlefield, Michael Patton, Pekka Savola, and Glenn Stump for their review and comments.
非常感谢马克·拜尔、吉姆·邦德、拉尔夫·德罗姆斯、罗伯特·埃尔兹、彼得·福特、奥拉弗尔·古德蒙德松、伊迪·冈特、安德烈亚斯·古斯塔夫松、大卫·W·汉金斯、R·巴尔·希布斯、金·金尼尔、关斯图尔特·柠檬、埃德·刘易斯、迈克尔·刘易斯、乔什·利特菲尔德、迈克尔·巴顿、佩卡·萨沃拉和格伦·斯图普的评论和评论。
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[1] Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[2] Stapp, M., Lemon, T., and A. Gustafsson, "A DNS Resource Record (RR) for Encoding Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR), RFC 4701, October 2006.
[2] Stapp，M.，Lemon，T.，和A.Gustafsson，“用于编码动态主机配置协议（DHCP）信息（DHCID RR）的DNS资源记录（RR），RFC 47012006年10月。
[3] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997.
[3] Vixie，P.，Thomson，S.，Rekhter，Y.，和J.Bound，“域名系统中的动态更新（DNS更新）”，RFC 21361997年4月。
[4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.
[4] Droms，R.，“动态主机配置协议”，RFC 2131，1997年3月。
[5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
[5] Droms，R.，Bound，J.，Volz，B.，Lemon，T.，Perkins，C.，和M.Carney，“IPv6的动态主机配置协议（DHCPv6）”，RFC3315，2003年7月。
[6] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.
[6] Mockapetris，P.，“域名-实现和规范”，STD 13，RFC 10351987年11月。
[7] Malkin, G., "Internet Users' Glossary", FYI 18, RFC 1983, August 1996.
[7] Malkin，G.“互联网用户词汇表”，第18财年，RFC 1983年，1996年8月。
[8] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host Configuration Protocol (DHCP) Client Fully Qualified Domain Name (FQDN) Option", RFC 4702, October 2006.
[8] Stapp，M.，Volz，B.，和Y.Rekhter，“动态主机配置协议（DHCP）客户端完全限定域名（FQDN）选项”，RFC 4702，2006年10月。
[9] Volz, B., "The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option", RFC 4704, October 2006.
[9] Volz，B.，“IPv6（DHCPv6）客户端完全限定域名（FQDN）选项的动态主机配置协议”，RFC 4704，2006年10月。
[10] Wellington, B., "Secure Domain Name System (DNS) Dynamic Update", RFC 3007, November 2000.
[10] 威灵顿，B.，“安全域名系统（DNS）动态更新”，RFC 3007，2000年11月。
[11] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers for Dynamic Host Configuration Protocol Version Four (DHCPv4)", RFC 4361, February 2006.
[11] Lemon，T.和B.Sommerfeld，“动态主机配置协议第四版（DHCPv4）的节点特定客户端标识符”，RFC 4361，2006年2月。
[12] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997.
[12] Alexander，S.和R.Droms，“DHCP选项和BOOTP供应商扩展”，RFC 21321997年3月。
[13] Vixie, P., Gudmundsson, O., Eastlake, D., and B. Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, May 2000.
[13] Vixie，P.，Gudmundsson，O.，Eastlake，D.，和B.Wellington，“DNS的密钥交易认证（TSIG）”，RFC 28452000年5月。
[14] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001.
[14] Droms，R.和W.Arbaugh，“DHCP消息的身份验证”，RFC31182001年6月。
Authors' Addresses
作者地址
Mark Stapp Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 USA
Mark Stapp Cisco Systems，Inc.美国马萨诸塞州Boxborough大道1414号，邮编01719
Phone: 978.936.1535 EMail: mjs@cisco.com
电话：978.936.1535电子邮件：mjs@cisco.com
Bernie Volz Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 USA
伯尼·沃兹思科系统公司，美国马萨诸塞州伯斯堡马萨诸塞大道1414号，邮编01719
Phone: 978.936.0382 EMail: volz@cisco.com
电话：978.936.0382电子邮件：volz@cisco.com
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