Internet Engineering Task Force (IETF) R. Johnson
Request for Comments: 6656 K. Kinnear
Category: Informational M. Stapp
ISSN: 2070-1721 Cisco Systems, Inc.
July 2012
Internet Engineering Task Force (IETF) R. Johnson
Request for Comments: 6656 K. Kinnear
Category: Informational M. Stapp
ISSN: 2070-1721 Cisco Systems, Inc.
July 2012
Description of Cisco Systems' Subnet Allocation Option for DHCPv4
描述Cisco Systems针对DHCPv4的子网分配选项
Abstract
摘要
This memo documents a DHCPv4 option that currently exists and was previously privately defined for the operation and usage of the Cisco Systems' Subnet Allocation Option for DHCPv4. The option is passed between the DHCPv4 Client and the DHCPv4 Server to request dynamic allocation of a subnet, give specifications of the subnet(s) allocated, and report usage statistics. This memo documents the current usage of the option in agreement with RFC 3942, which declares that any preexisting usages of option numbers in the range 128-223 should be documented and that the working group will try to officially assign those numbers to those options.
本备忘录记录了一个DHCPv4选项，该选项目前存在，并且以前是为运行和使用Cisco Systems针对DHCPv4的子网分配选项而私下定义的。该选项在DHCPv4客户端和DHCPv4服务器之间传递，以请求动态分配子网，给出所分配子网的规格，并报告使用情况统计信息。本备忘录记录了与RFC 3942一致的期权的当前使用情况，RFC 3942声明，应记录128-223范围内期权编号的任何先前使用情况，工作组将尝试将这些编号正式分配给这些期权。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6656.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6656.
Copyright Notice
版权公告
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2012 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
本文件可能包含2008年11月10日之前发布或公开的IETF文件或IETF贡献中的材料。控制某些材料版权的人员可能未授予IETF信托允许在IETF标准流程之外修改此类材料的权利。在未从控制此类材料版权的人员处获得充分许可的情况下，不得在IETF标准流程之外修改本文件，也不得在IETF标准流程之外创建其衍生作品，除了将其格式化以RFC形式发布或将其翻译成英语以外的其他语言。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Subnet Allocation Option Format . . . . . . . . . . . . . . . 5
3.1. Subnet-Request Suboption Format . . . . . . . . . . . . . 5
3.2. Subnet-Information Suboption Format . . . . . . . . . . . 7
3.2.1. Subnet Prefix Information Block Format . . . . . . . . 8
3.3. Subnet-Name Suboption Format . . . . . . . . . . . . . . . 9
3.4. Suggested-Lease-Time Suboption Format . . . . . . . . . . 10
4. Requesting Allocation of a Subnet . . . . . . . . . . . . . . 10
4.1. Client DHCPDISCOVER Message . . . . . . . . . . . . . . . 11
4.2. Server DHCPOFFER Message . . . . . . . . . . . . . . . . . 11
4.3. Client DHCPREQUEST Message . . . . . . . . . . . . . . . . 12
4.4. Server DHCPACK Message . . . . . . . . . . . . . . . . . . 13
5. Client Renewal of Subnet Lease . . . . . . . . . . . . . . . . 13
5.1. Client RENEW DHCPREQUEST Message . . . . . . . . . . . . . 13
5.2. Server RENEW DHCPREQUEST Response . . . . . . . . . . . . 14
5.3. Client DHCPRELEASE Message . . . . . . . . . . . . . . . . 14
5.4. Server DHCPFORCERENEW Message . . . . . . . . . . . . . . 15
6. Client Requesting Previously Allocated Subnet Information . . 15
6.1. Initial Client DHCPDISCOVER Message . . . . . . . . . . . 15
6.2. Initial Server DHCPOFFER Response . . . . . . . . . . . . 16
6.3. Additional Client DHCPDISCOVER Messages . . . . . . . . . 16
6.4. Additional Server DHCPOFFER Responses . . . . . . . . . . 16
7. DHCP Server Subnet Allocation Method . . . . . . . . . . . . . 17
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 19
9. Differences from DHCPv6 Prefix Delegation . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 23
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Subnet Allocation Option Format . . . . . . . . . . . . . . . 5
3.1. Subnet-Request Suboption Format . . . . . . . . . . . . . 5
3.2. Subnet-Information Suboption Format . . . . . . . . . . . 7
3.2.1. Subnet Prefix Information Block Format . . . . . . . . 8
3.3. Subnet-Name Suboption Format . . . . . . . . . . . . . . . 9
3.4. Suggested-Lease-Time Suboption Format . . . . . . . . . . 10
4. Requesting Allocation of a Subnet . . . . . . . . . . . . . . 10
4.1. Client DHCPDISCOVER Message . . . . . . . . . . . . . . . 11
4.2. Server DHCPOFFER Message . . . . . . . . . . . . . . . . . 11
4.3. Client DHCPREQUEST Message . . . . . . . . . . . . . . . . 12
4.4. Server DHCPACK Message . . . . . . . . . . . . . . . . . . 13
5. Client Renewal of Subnet Lease . . . . . . . . . . . . . . . . 13
5.1. Client RENEW DHCPREQUEST Message . . . . . . . . . . . . . 13
5.2. Server RENEW DHCPREQUEST Response . . . . . . . . . . . . 14
5.3. Client DHCPRELEASE Message . . . . . . . . . . . . . . . . 14
5.4. Server DHCPFORCERENEW Message . . . . . . . . . . . . . . 15
6. Client Requesting Previously Allocated Subnet Information . . 15
6.1. Initial Client DHCPDISCOVER Message . . . . . . . . . . . 15
6.2. Initial Server DHCPOFFER Response . . . . . . . . . . . . 16
6.3. Additional Client DHCPDISCOVER Messages . . . . . . . . . 16
6.4. Additional Server DHCPOFFER Responses . . . . . . . . . . 16
7. DHCP Server Subnet Allocation Method . . . . . . . . . . . . . 17
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 19
9. Differences from DHCPv6 Prefix Delegation . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 23
This memo documents a DHCP option [RFC2132], the Subnet Allocation option, that was developed by Cisco and allows a DHCP Client to allocate a subnet given information from a DHCP Server. This protocol makes use of DHCP option number 220, one of the option numbers reclassified by [RFC3942]. That RFC specifies in Section 4, procedure 2, "Vendors that currently use one or more of the reclassified options have 6 months following this RFC's publication date to notify the DHC WG and IANA that they are using particular options numbers and agree to document that usage in an RFC". This memo serves as that documentation. The DHC WG has had no input into any of the details of the protocol operation and makes no statement about the correctness or any other aspect of the protocol. The WG also has seen no interest in further implementation or deployment of this protocol other than privately, and therefore has decided to publish this document solely for informational purposes.
此备忘录记录了一个DHCP选项[RFC2132]，子网分配选项，由Cisco开发，允许DHCP客户端从DHCP服务器分配给定信息的子网。该协议使用DHCP选项编号220，这是[RFC3942]重新分类的选项编号之一。RFC在第4节程序2中规定，“目前使用一个或多个重新分类选项的供应商在RFC发布日期后有6个月的时间通知DHC WG和IANA他们正在使用特定选项编号，并同意在RFC中记录该使用情况”。这份备忘录就是那份文件。DHC工作组没有对协议操作的任何细节进行任何输入，也没有对协议的正确性或任何其他方面做出任何声明。工作组还认为，除了私下之外，没有人对进一步实施或部署本协议感兴趣，因此决定仅出于信息目的发布本文件。
The Subnet Allocation option provides a straightforward way to allocate a subnet from DHCP, useful for a simple Dial-in Aggregation box, or to implement a Hierarchical chain of DHCP Servers, each one in turn leasing one or more subnets to the next DHCP Server down the chain. This option is specified in such a way as to use one DHCP option number, while using suboption numbers for each function.
Subnet Allocation（子网分配）选项提供了一种从DHCP分配子网的简单方法，可用于简单的拨入聚合框，或用于实现DHCP服务器的分层链，每个服务器依次将一个或多个子网出租给链下游的下一个DHCP服务器。指定此选项的方式是使用一个DHCP选项号，同时为每个函数使用子选项号。
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 [RFC2119].
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[RFC2119]中所述进行解释。
This document also uses the following terms:
本文件还使用以下术语：
DHCP Client: DHCP Client or "Client" is an Internet host using DHCP to obtain configuration parameters such as a network address.
DHCP客户端：DHCP客户端或“客户端”是使用DHCP获取配置参数（如网络地址）的Internet主机。
DHCP Server: A DHCP Server or "Server" is an Internet host that returns configuration parameters to DHCP Clients.
DHCP服务器：DHCP服务器或“服务器”是向DHCP客户端返回配置参数的Internet主机。
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Code | Len | Flags | Suboptions ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Code | Len | Flags | Suboptions ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Code = Subnet Allocation option code (1 octet): 220 Len = Length of the entire option including all suboptions (1 octet) Flags = Various flags: (None currently defined)
代码=子网分配选项代码（1个八位字节）：220 Len=整个选项的长度，包括所有子选项（1个八位字节）标志=各种标志：（当前未定义）
One or more suboptions may be specified as described below.
可以如下所述指定一个或多个子选项。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Len | Flags :i:h| Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Len | Flags :i:h| Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Len = Length of the suboption (always 2 for this suboption) (1 octet) Flags = Flags field. (all unused bits must be zero)
Len=子选项的长度（此子选项始终为2）（1个八位组）Flags=Flags字段。（所有未使用的位必须为零）
'h' = Hierarchical flag 1 : Client will be allocating addresses from this subnet. 0 : Client will be relaying DHCP requests to the Server from this subnet. 'i' = Information flag 1 : Client is seeking information about previously allocated subnets. 0 : Client is seeking a new subnet allocation.
“h”=分层标志1：客户端将从此子网分配地址。0:客户端将从此子网向服务器中继DHCP请求。'i'=信息标志1：客户端正在查找有关以前分配的子网的信息。0:客户端正在寻求新的子网分配。
Prefix = Network prefix length requested (0 means no suggested length is given) (1 octet)
前缀=请求的网络前缀长度（0表示未给出建议长度）（1个八位组）
The DHCP Server SHOULD NOT include the Subnet Request suboption in any replies to the DHCP Client. Enough information will be present in the Subnet-Information suboption, such that the Subnet Request suboption is not needed in replies to the Client.
DHCP服务器不应在对DHCP客户端的任何答复中包含子网请求子选项。“子网信息”子选项中将提供足够的信息，因此在答复客户端时不需要“子网请求”子选项。
The DHCP Server SHOULD allocate a subnet with prefix length [RFC4632] less than or equal to the "Prefix" field length specified in the request. In other words, a subnet containing a number of addresses at least the size indicated by the prefix length requested and
DHCP服务器应分配前缀长度[RFC4632]小于或等于请求中指定的“前缀”字段长度的子网。换句话说，包含多个地址的子网，地址的大小至少与请求的前缀长度和
possibly more. The DHCP Server MAY allocate a subnet with a prefix length greater than that specified in the request (or a subnet with a number of addresses less than requested), but this is not encouraged.
可能更多。DHCP服务器可以分配前缀长度大于请求中指定长度的子网（或地址数小于请求数的子网），但不鼓励这样做。
A "Prefix" field size of 0 MAY be specified by the DHCP Client. In this case, no suggested prefix length is given.
DHCP客户端可以指定0的“前缀”字段大小。在这种情况下，没有给出建议的前缀长度。
Multiple Subnet-Request suboptions in a DHCP packet indicate that multiple subnets are being requested. Note that multiple occurrences of this suboption MUST NOT be concatenated in the sense of [RFC3396].
DHCP数据包中的多个子网请求子选项表示正在请求多个子网。请注意，在[RFC3396]的意义上，此子选项的多次出现不得连接。
Each Subnet-Request suboption MUST result in no more than one Subnet-Information suboption in the DHCPOFFER message from the Server, and may result in no Subnet-Information suboptions.
每个子网请求子选项在来自服务器的DHCPOFFER消息中只能产生一个子网信息子选项，并且可能不会产生子网信息子选项。
The Client MAY also include the Subnet-Information suboption in order to request a particular subnet. In this case, the Client SHOULD only include one Subnet-Request suboption, since it would otherwise be unclear which Subnet-Information suboption referred to which Subnet-Request suboption. Multiple subnet requests can be made by sending multiple DHCPDISCOVER packets.
客户端还可以包括子网信息子选项以请求特定子网。在这种情况下，客户端应该只包含一个子网请求子选项，因为不清楚哪个子网信息子选项引用哪个子网请求子选项。通过发送多个DHCPDISCOVER数据包，可以发出多个子网请求。
Setting the 'h' flag to 1 indicates the Client will be allocating addresses from the allocated subnet(s) itself. This can be thought of as a "Hierarchical DHCP" design in that control of allocation for the subnet(s) will be passed to the Client.
将“h”标志设置为1表示客户端将从分配的子网本身分配地址。这可以被认为是一种“分层DHCP”设计，因为子网的分配控制将传递给客户端。
Setting the 'h' flag to 0 indicates the Client wants the DHCP Server to retain control over allocation of addresses from the subnet(s). Any address allocation requests on the subnet will be relayed back to the DHCP Server.
将“h”标志设置为0表示客户端希望DHCP服务器保留对来自子网的地址分配的控制。子网上的任何地址分配请求都将中继回DHCP服务器。
Setting the 'i' flag to 1 indicates the Client is NOT seeking allocation of any subnets, but is simply seeking information from the Server as to what subnet(s) have been allocated (or reserved) for this Client. If the 'i' flag is set to 1, then the "Prefix" field SHOULD be set to 0 and MUST be ignored by the Server. In this case, the conversation between the Client and the Server will only progress to the DHCPOFFER packet from the Server, giving the information, as described in Section 6 below.
将“i”标志设置为1表示客户端不寻求任何子网的分配，而只是从服务器寻求关于已为此客户端分配（或保留）了哪些子网的信息。如果“i”标志设置为1，则“Prefix”字段应设置为0，服务器必须忽略该字段。在这种情况下，客户机和服务器之间的对话将只从服务器进入DHCPOFFER数据包，提供信息，如下面第6节所述。
Any undefined flags (those other than 'i' and 'h', mentioned above) should be ignored by the DHCP Server.
DHCP服务器应忽略任何未定义的标志（上述“i”和“h”以外的标志）。
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| 2 | Len | Flags :c:s| SP1, SP2, ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| 2 | Len | Flags :c:s| SP1, SP2, ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Len = Length of the suboption (min. length of 8) (1 octet) Flags = Various flags that apply to ALL Subnet Prefix Information fields specified in this suboption. Unused flags must be zero.
Len=子选项的长度（最小长度为8）（1个八位字节）标志=适用于此子选项中指定的所有子网前缀信息字段的各种标志。未使用的标志必须为零。
'c' : Client flag (explained below) 1 : This information is in response to a Client request (or has been echoed back by the Client, when asking for the next previously allocated subnet from the Server). 0 : Otherwise. 's' : Server flag (explained below) 1 : Server has additional subnet information for this Client. 0 : Otherwise.
“c”：客户机标志（如下所述）1：此信息响应客户机请求（或在从服务器请求以前分配的下一个子网时，客户机已回显）。0:否则。”s'：服务器标志（如下所述）1:服务器具有此客户端的其他子网信息。0:否则。
SP1, SP2, ... Subnet Prefix Information blocks as specified below (variable size)
SP1，SP2。。。下面指定的子网前缀信息块（可变大小）
Setting the 'c' flag to 1 indicates this Subnet-Information suboption is in response to a Client request for information from the Server as to what subnet(s) have been allocated. This flag is used in response to a Subnet-Request suboption with the 'i' flag set and should be 0 in other Server responses. Note, the flag is echoed back from the Client to the Server when requesting the "next previously allocated subnet". Another way to think of the 'c' bit would be that it indicates that the subnet information contained in this suboption does not represent a new allocation by the Server or a new request for allocation by the Client, but instead represents previously allocated subnet information.
将“c”标志设置为1表示此子网信息子选项响应客户端请求服务器提供有关已分配子网的信息。此标志用于响应设置了“i”标志的子网请求子选项，在其他服务器响应中应为0。注意，当请求“下一个先前分配的子网”时，该标志从客户端回显到服务器。考虑“c”位的另一种方式是，它表示此子选项中包含的子网信息并不表示服务器的新分配或客户端的新分配请求，而是表示以前分配的子网信息。
Setting the 's' flag to 1 indicates the Server has additional subnet information for the Client.
将“s”标志设置为1表示服务器具有客户端的其他子网信息。
Any undefined flags (those other than 'c' and 's', mentioned above) should be ignored by the DHCP Server.
DHCP服务器应忽略任何未定义的标志（上述“c”和“s”以外的标志）。
The Subnet-Information suboption is used by the DHCP Server in order to return information as to what subnets are offered (in the case of a DHCPOFFER packet) or allocated (in the case of a DHCPACK packet). As is indicated above, multiple subnets may be returned in one Subnet-Information suboption.
DHCP服务器使用Subnet Information（子网信息）子选项，以返回关于提供了哪些子网（在DHCPOFFER数据包的情况下）或分配了哪些子网（在DHCPACK数据包的情况下）的信息。如上所述，在一个子网信息子选项中可以返回多个子网。
The Subnet-Information suboption is also used by the DHCP Client in order to request allocation of specific subnets in a DHCPREQUEST packet. In this case, the "Network", "Prefix", and "Flags" fields contained in the associated Subnet Prefix Information blocks MUST NOT be changed from the information that was received in the DHCPOFFER packet from the Server. The Client MAY, however, use multiple Subnet-Information suboptions in order to request subnets that were originally specified by the Server inside one Subnet-Information suboption.
DHCP客户端还使用子网信息子选项来请求在DHCPREQUEST数据包中分配特定子网。在这种情况下，关联子网前缀信息块中包含的“网络”、“前缀”和“标志”字段不得与DHCPOFFER数据包中从服务器接收到的信息进行更改。但是，客户机可以使用多个子网信息子选项，以便在一个子网信息子选项内请求最初由服务器指定的子网。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix | Flags :h:d| Stat-len | Optional stats...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix | Flags :h:d| Stat-len | Optional stats...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network = IPv4 network number (4 octets) Prefix = Prefix length (1 octet) Flags = Flags field (Undefined bits must be zero) (1 octet)
网络=IPv4网络号（4个八位字节）前缀=前缀长度（1个八位字节）标志=标志字段（未定义的位必须为零）（1个八位字节）
'd' = Deprecate flag (explained below) 1 : Deprecation of this subnet is requested. 0 : No deprecation is needed.
“d”=弃用标志（解释如下）1:请求弃用此子网。0:不需要弃用。
'h' = Hierarchical flag (explained below) 1 : Client will be allocating addresses from this subnet. 0 : Client will be relaying DHCP requests to the Server from this subnet.
“h”=分层标志（如下所述）1:客户端将从此子网分配地址。0:客户端将从此子网向服务器中继DHCP请求。
Stat-len = Length of the optional statistics information field (zero if no statistics are included) (1 octet)
Stat len=可选统计信息字段的长度（如果不包括统计信息，则为零）（1个八位字节）
The 'd' flag may only be returned by the Server to the Client (inside a DHCPACK packet, in response to a DHCP RENEW). Its presence means that the Client should prepare to give up the subnet. For example, if the Client is assigning addresses from this subnet to other Clients, it should cease doing so immediately and should not renew
“d”标志只能由服务器返回给客户端（在DHCPACK数据包内，响应DHCP续订）。它的存在意味着客户端应该准备放弃子网。例如，如果客户端正在将此子网中的地址分配给其他客户端，则应立即停止分配，并且不应续订
any leases when Clients ask for renewal. As soon as all addresses in the subnet are unallocated, the Client should send a DHCPRELEASE message to the Server, including a Subnet Prefix Information block for the subnet in order to release the subnet. The format of this message is described farther below.
客户要求续约时的任何租赁。一旦子网中的所有地址都未分配，客户端应立即向服务器发送DHCPRELEASE消息，包括子网的子网前缀信息块，以便释放子网。下面将进一步描述此消息的格式。
The 'h' flag tells the Client how the Server intends for the Client to use the allocated subnet. It is interpreted in the same manner as that in the Subnet-Request suboption. In response to a Subnet-Request, the Server should normally specify the 'h' flag in the same manner as it was in the Subnet-Request suboption from the Client. The Server MAY, however, change the 'h' flag from that specified in the Subnet-Request suboption if it has been configured to override the Client's request.
“h”标志告诉客户端服务器打算让客户端如何使用分配的子网。它的解释方式与子网请求子选项中的解释方式相同。为了响应子网请求，服务器通常应以与客户端的子网请求子选项中相同的方式指定“h”标志。但是，如果已将服务器配置为覆盖客户端的请求，则服务器可以更改子网请求子选项中指定的“h”标志。
Any undefined flags (those other than 'd' and 'h', mentioned above) should be ignored by the DHCP Server.
DHCP服务器应忽略任何未定义的标志（上述“d”和“h”以外的标志）。
If any usage statistics information is to be included, then the "Stat-len" field specifies the number of bytes of statistics information that is included. See below for more information. If no statistics information is included, then this byte MUST be zero. The "Stat-len" field SHOULD always be zero when this suboption is sent by the DHCP Server. The usage statistics information is intended for use only to report usage statistics from the Client to the Server.
如果要包含任何使用统计信息，“Stat len”字段指定包含的统计信息的字节数。有关更多信息，请参见下文。如果未包含统计信息，则该字节必须为零。当DHCP服务器发送此子选项时，“Stat len”字段应始终为零。使用情况统计信息仅用于报告从客户端到服务器的使用情况统计信息。
The Subnet-Information suboption may also include usage statistics information. If this information is included, then the "Stat-len" (Statistics length) field MUST be set to the number of bytes of statistics information that is being included. The statistics information MUST be in the following form and order:
子网信息子选项还可以包括使用统计信息。如果包含此信息，则“Stat len”（统计长度）字段必须设置为包含的统计信息的字节数。统计信息必须采用以下形式和顺序：
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| High water |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Currently in use |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unusable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| High water |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Currently in use |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unusable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
"High water" refers the to "high-water mark" of allocated addresses within the subnet. That is, the largest number of addresses that were ever allocated at one time from the subnet.
“高水位”是指子网内分配地址的“高水位线”。也就是说，一次从子网分配的最大地址数。
"Currently in use" refers to the number of addresses currently allocated in the subnet.
“当前正在使用”是指子网中当前分配的地址数。
"Unusable" refers to the number of addresses that are currently unusable for any reason (such as a Client returning a DHCPDECLINE, or finding the address already in use).
“不可用”是指由于任何原因（如客户端返回DHCPDecend或发现已在使用的地址）当前不可用的地址数。
Additional statistics may be added to this option in the future. If so, they MUST be appended immediately after the already defined statistics fields. All statistics fields MUST remain in the same order. Use the all ones value (0xffff) in order to skip reporting a number for a particular field. Fewer fields may be included than what is specified above; for example, if "Stat-len" is "4", then the "Unusable" field has not been included. All fields that are included MUST remain in order specified here.
将来可能会在此选项中添加其他统计信息。如果是这样，则必须在已定义的统计字段之后立即追加这些字段。所有统计字段必须保持相同的顺序。使用all ones值（0xffff）跳过报告特定字段的数字。可能包含的字段少于上面指定的字段；例如，如果“Stat len”为“4”，则未包括“Unusable”字段。包含的所有字段必须保持此处指定的顺序。
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| 3 | Len | Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| 3 | Len | Name ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Len = length of the suboption (min. length of 1) (1 octet)
Len=子选项的长度（最小长度为1）（1个八位组）
The Subnet-Name suboption may be used in order to pass a subnet name to the Server for use during allocation. This name may be used for any purpose but is intended to tell the Server something extra about the needed subnet; for example, "sales department", "customer 1002", "address pool FOO", or some such. The "name" should NOT be NULL terminated since the "len" field already specifies the length of the name. The "Name" in this suboption MUST be given using UTF-8 [RFC3629].
子网名称子选项可用于将子网名称传递给服务器，以便在分配期间使用。此名称可用于任何目的，但旨在告诉服务器有关所需子网的额外信息；例如，“销售部门”、“客户1002”、“地址池FOO”等。“name”不应以NULL结尾，因为“len”字段已经指定了名称的长度。此子选项中的“名称”必须使用UTF-8[RFC3629]给出。
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Len (4) | t1 | t2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| t3 | t4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Len (4) | t1 | t2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| t3 | t4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Len = length of the suboption (always 4 for this suboption) (1 octet)
Len=子选项的长度（此子选项始终为4）（1个八位组）
The Suggested-Lease-Time suboption MAY be included by the Server in order to suggest the lease time to be used by the Client when allocating addresses from the subnet allocated. The 4-octet value of the lease time is in the same format as that of the "IP Address Lease Time" option (option 51), as described in [RFC2132].
服务器可以包括建议的租用时间子选项，以便建议客户端在从分配的子网分配地址时使用的租用时间。如[RFC2132]所述，租用时间的4个八位字节值与“IP地址租用时间”选项（选项51）的格式相同。
If included, this suboption MUST appear only once. (Inclusion of multiple such suboptions would result in ambiguity as to which applied to which subnet.) If different suggested lease times are needed, the Server SHOULD, instead, reply with only one offered subnet and should set the "Server flag" in the Subnet-Information suboption to indicate to the Client that it should send another subnet request to gather the others.
如果包含，则此子选项只能出现一次。（包含多个这样的子选项会导致应用于哪个子网的不明确。）如果需要不同的建议租用时间，服务器应该只回复一个提供的子网，并且应该设置“服务器标志”在子网信息子选项中，指示客户端应发送另一个子网请求以收集其他子网请求。
The Client SHOULD use a lease time, when allocating addresses from the subnet, that is the lesser of the remaining lease time of the subnet itself and the Suggested-Lease-Time suboption.
从子网分配地址时，客户端应使用租用时间，即子网本身的剩余租用时间和建议的租用时间子选项中的较小者。
The DHCP Client creates a DHCPDISCOVER message including the Subnet Allocation option, and its set of suboptions, to request allocation of a subnet. The DHCP Client should include the Subnet-Request suboption, specifying the prefix length of the subnet requested. The 'h' bit should be set to 1 if the Client intends to control allocation of addresses within the subnet itself, or 0 if the Server should retain control of addresses within the subnet. More than one Subnet Allocation option may appear in a DHCPDISCOVER message; however, the Client SHOULD limit the number of requests, noting that the DHCP replies will need to include the Subnet-Information suboption, which takes up more space than the Subnet-Request suboption.
DHCP客户端创建一条DHCPDISCOVER消息，其中包括子网分配选项及其子选项集，以请求分配子网。DHCP客户端应包含子网请求子选项，指定所请求子网的前缀长度。如果客户端打算控制子网内的地址分配，则“h”位应设置为1；如果服务器应保留子网内地址的控制权，则“h”位应设置为0。DHCPDISCOVER消息中可能会出现多个子网分配选项；但是，客户端应该限制请求的数量，注意DHCP应答需要包括子网信息子选项，它比子网请求子选项占用更多的空间。
If more than one subnet is being requested, multiple Subnet-Request suboptions MAY be included or multiple DHCPDISCOVER messages MAY be sent instead. The prefix length field of each Subnet-Request suboption MUST be either 0, or in the range of 1 to 30 inclusive.
如果正在请求多个子网，则可能会包含多个子网请求子选项，或者可能会发送多条DHCPDISCOVER消息。每个子网请求子选项的前缀长度字段必须为0，或在1到30（包括1到30）的范围内。
The DHCP "IP address lease time" option (code 51) MAY be included in the DHCPDISCOVER message to specify the lease time the Client is requesting for the subnet. If not present, no suggested lease time is given.
DHCP“IP地址租用时间”选项（代码51）可包含在DHCPDISCOVER消息中，以指定客户端请求子网的租用时间。如果不存在，则不提供建议的租赁时间。
The DHCP "Client ID" option (code 61) MAY be included in the DHCPDISCOVER message as it may be used by the Server in performing the subnet allocation.
DHCP“客户机ID”选项（代码61）可包括在DHCPDISCOVER消息中，因为服务器可在执行子网分配时使用该选项。
Upon receiving a DHCPDISCOVER containing the Subnet Allocation option, the DHCP Server SHOULD respond with a DHCPOFFER message including the Subnet-Information suboption in order to specify the subnet(s) that it is willing to allocate to the Client in order to fulfill the request(s).
在接收到包含子网分配选项的DHCPDISCOVER后，DHCP服务器应使用包含子网信息子选项的DHCPOFFER消息进行响应，以指定它愿意分配给客户端的子网，以满足请求。
The Server need not reserve the subnets that are being offered, but SHOULD not offer the same subnets to another DHCP Client until a reasonable time period (implementation dependent) has passed. (This is similar to normal DHCP address allocation.)
服务器无需保留正在提供的子网，但在经过合理的时间段（取决于实现）之前，不应向另一个DHCP客户端提供相同的子网。（这类似于正常的DHCP地址分配。）
The Server MUST NOT include the Subnet-Request suboption in the DHCPOFFER. The same information is already present in the Subnet Information suboption(s) that SHOULD be included in the DHCPOFFER.
服务器不得在DHCPOFFER中包含子网请求子选项。应包含在DHCPOFFER中的子网信息子选项中已存在相同的信息。
The Server SHOULD also include the IP address lease time option (option 51) in the DHCPOFFER message. This gives the lease time for all subnets given in all Subnet-Request suboptions contained in the DHCPOFFER message. The Server MAY also include the Renewal and/or Rebinding options in order to further control the "T1" and "T2" lease timers of the Client. There MUST be exactly one IP address lease time (and optionally one Rebinding and/or one Renewal option) in the DHCPOFFER message.
服务器还应在DHCPOFFER消息中包含IP地址租用时间选项（选项51）。这将给出DHCPOFFER消息中包含的所有子网请求子选项中给定的所有子网的租用时间。服务器还可以包括续订和/或重新绑定选项，以便进一步控制客户端的“T1”和“T2”租赁定时器。DHCPOFFER消息中必须只有一个IP地址租用时间（以及可选的一个重新绑定和/或一个续订选项）。
The Server MAY set the "Server flag" ('s') to 1 to indicate that it would like to allocate one or more additional subnet(s) to the Client. This indicates that the Client should send another DHCPDISCOVER message specifying a prefix length field, P, of zero in order to request the additional subnet allocation(s) information. This may be necessary if the subnets are to be allocated with different lease times, for example.
服务器可以将“服务器标志”（'s'）设置为1，以指示它希望将一个或多个附加子网分配给客户端。这表示客户端应发送另一条DHCPDISCOVER消息，指定前缀长度字段P为零，以便请求附加子网分配信息。例如，如果子网要分配不同的租用时间，这可能是必要的。
The "Client flag" ('c') MUST be set to 0 to indicate this is a Server response to a Client request for a new subnet allocation and not a response to a request for information about already allocated subnets.
“客户端标志”（'c'）必须设置为0，以指示这是对客户端请求的新子网分配的服务器响应，而不是对请求有关已分配子网的信息的响应。
If the packet contains a Subnet Allocation option, the Server SHOULD set the DHCP yiaddr value to all zeros (0.0.0.0) and the Client MUST ignore fields having to do with address assignment. In other words, a DHCP packet exchange cannot provide subnet allocation and address assignment simultaneously.
如果数据包包含子网分配选项，服务器应将DHCP yiaddr值设置为全零（0.0.0.0），客户端必须忽略与地址分配有关的字段。换句话说，DHCP数据包交换不能同时提供子网分配和地址分配。
When sending a DHCPREQUEST, the Client MUST NOT modify any fields of any Subnet-Information suboptions received from the Server. However, the Client MAY choose not to include some Subnet-Information suboptions when issuing the DHCPREQUEST. Subnet-Request suboptions MUST NOT be included in the DHCPREQUEST message; only the Subnet-Information suboption(s) should be included.
发送DHCPREQUEST时，客户端不得修改从服务器接收的任何子网信息子选项的任何字段。但是，客户端在发出DHCPREQUEST时可能会选择不包含某些子网信息子选项。DHCPREQUEST消息中不得包含子网请求子选项；仅应包括子网信息子选项。
The DHCP Server, upon receipt of the Client's DHCPREQUEST message, MAY refuse allocation of any subnets (for example, if they have been allocated elsewhere in the meantime); however, since the Server should have set aside the subnets offered for a short period of time, and since the Client should have requested the subnets within a short period of time after receiving the offer(s) from the Server(s), this last minute rejection should be rare. The DHCP Server MUST NOT change the network number(s) or prefix length(s); however, it MAY remove some Subnet-Information suboptions from the list.
DHCP服务器在收到客户端的DHCPREQUEST消息后，可以拒绝任何子网的分配（例如，如果同时在其他地方分配了子网）；但是，由于服务器应在短时间内留出提供的子网，并且由于客户端应在收到服务器提供的服务后的短时间内请求子网，因此最后一分钟的拒绝应该很少。DHCP服务器不得更改网络号或前缀长度；但是，它可能会从列表中删除某些子网信息子选项。
The Server SHOULD include the IP address lease time option specifying the lease period for all subnet(s) in the DHCPACK. All subnets allocated in one DHCP message will have the same lease time, and only one IP address lease time option must appear in the DHCP message.
服务器应包括IP地址租用时间选项，指定DHCPACK中所有子网的租用期。在一条DHCP消息中分配的所有子网将具有相同的租用时间，并且DHCP消息中只能出现一个IP地址租用时间选项。
If the Server has internal information that states that the Client should be allocated more subnets than were requested, the Server MAY set the 's' bit in the last Subnet-Information suboption to indicate that the Client needs to request more subnets (as described above).
如果服务器的内部信息表明应为客户端分配比请求的子网更多的子网，则服务器可以在最后一个子网信息子选项中设置“s”位，以指示客户端需要请求更多的子网（如上所述）。
The allocable unit is the tuple (network number, prefix length). Multiple subnets may be allocated in one DHCPACK; however, since there can be only one Lease-time option, each subnet allocated is assigned the same lease time. Each subnet lease tuple (network number, prefix length) MAY be renewed or released individually.
可分配的单位是元组（网络号、前缀长度）。在一个DHCPACK中可以分配多个子网；但是，由于只能有一个租用时间选项，因此分配的每个子网都分配了相同的租用时间。每个子网租约元组（网络号、前缀长度）可以单独续订或释放。
The Client MUST renew all subnets allocated with a lease time in much the same manner as renewing an allocated IP address. Renewal timers need not be set in exactly the same manner, however. If Renewal and/or Rebinding options were included in the DHCPACK of the subnet allocation, then these "T1" and "T2" timers should be used just as they would be in the case of address allocation timers.
客户端必须以与续订已分配的IP地址大致相同的方式续订以租赁时间分配的所有子网。然而，续费计时器不需要以完全相同的方式设置。如果子网分配的DHCPACK中包含续订和/或重新绑定选项，则应使用这些“T1”和“T2”计时器，就像在地址分配计时器中一样。
The DHCPREQUEST message MUST include a Subnet-Information suboption for which the Client is seeking renewal of the lease. This Subnet-Information suboption may optionally include subnet usage statistics, as described above in Section 3.2 ("Subnet-Information Suboption Format").
DHCPREQUEST消息必须包含一个子网信息子选项，客户端正在为其寻求续订租约。如上文第3.2节（“子网信息子选项格式”）所述，此子网信息子选项可选择性地包括子网使用统计信息。
The subnet network number field ("Network") and subnet prefix length field ("Prefix") MUST agree with the values as they were originally allocated to the Client by the Server. In any of the statistics fields (High water, Currently in use, Unusable), a value of all ones (0xffff) SHOULD be used if the Client has no information to report for a statistic.
子网网络编号字段（“网络”）和子网前缀长度字段（“前缀”）必须与服务器最初分配给客户端的值一致。在任何统计字段（高水位、当前正在使用、不可用）中，如果客户机没有统计信息可报告，则应使用所有值（0xffff）。
The Server MAY respond to a subnet RENEW with either a DHCPACK or DHCPNAK response. If a DHCPNAK response is given, the Client MUST immediately stop using the subnet(s) specified and, if possible, notify all Clients with addresses allocated from this subnet that their addresses are no longer valid. The Client MAY, of course, send a DHCPDISCOVER message containing the Subnet Allocation option and the Subnet-Request suboption in order to acquire another subnet for use. In general, the Server should ask the Client to deprecate subnets by using the 'd' bit of the Subnet-Information suboption in a DHCPACK message (see below).
服务器可以使用DHCPACK或DHCPNAK响应来响应子网续订。如果给出DHCPNAK响应，则客户端必须立即停止使用指定的子网，并在可能的情况下，通知从该子网分配地址的所有客户端其地址不再有效。当然，客户端可以发送包含子网分配选项和子网请求子选项的DHCPDISCOVER消息，以便获取另一个子网以供使用。通常，服务器应该要求客户端通过在DHCPACK消息中使用子网信息子选项的“d”位来弃用子网（见下文）。
If a DHCPACK response is given, the "Deprecate" ('d') bit of the Flags field in the Subnet-Information suboption may also be set. This indicates the DHCP Client should prepare to stop using this subnet. If the Client is allocating IP addresses for other Clients from this subnet (e.g., via DHCP), the Client SHOULD immediately stop allocating such addresses. Once all allocated addresses in the subnet have been released, the Client SHOULD send a DHCPRELEASE message, including the Subnet-Information suboption (with optional usage statistics) in order to release the subnet(s) back to the Server.
如果给出DHCPACK响应，还可以设置子网信息子选项中标志字段的“Deprecate”（'d'）位。这表示DHCP客户端应准备停止使用此子网。如果客户端正在为此子网（例如，通过DHCP）为其他客户端分配IP地址，则客户端应立即停止分配此类地址。释放子网中所有分配的地址后，客户端应发送DHCPRELEASE消息，包括子网信息子选项（具有可选的使用统计信息），以便将子网释放回服务器。
The DHCP Client SHOULD send a DHCPRELEASE message in order to release allocated subnet(s) back to the Server when it is finished using them. This message MUST NOT include the Subnet-Request suboption, but MUST include one or more Subnet-Information suboptions, and may optionally include usage statistics.
DHCP客户端应发送一条DHCPRELEASE消息，以便在完成使用分配的子网后将其释放回服务器。此消息不得包含子网请求子选项，但必须包含一个或多个子网信息子选项，并且可以选择包含使用情况统计信息。
The Client MUST release the same subnet(s) of the same prefix length ("Prefix"), as were originally allocated. The Client MAY release a subset of the subnets that were allocated originally. In other
客户端必须释放与最初分配的前缀长度（“前缀”）相同的子网。客户端可以释放最初分配的子网的子集。换句话说
words, the allocable unit is the tuple (network number, prefix length). Multiple subnets may be allocated in one DHCPACK; however, each subnet MAY be released individually.
换句话说，可分配的单位是元组（网络号、前缀长度）。在一个DHCPACK中可以分配多个子网；但是，每个子网可以单独释放。
The DHCP Server MAY issue a DHCPFORCERENEW [RFC3203] message containing the Subnet Allocation option and the Subnet-Information suboption. Upon receiving this message, the DHCP Client MUST issue a DHCPREQUEST message to the DHCP Server in order to renew the lease on the subnet mentioned. No other subnets allocated to the Client are affected. As is the case with all DHCP RENEW messages, the Client may include subnet usage information in the Subnet-Information suboption in order to report subnet usage statistics, or set the "Stat-len" field to 0 if no statistics are to be reported.
DHCP服务器可能会发出包含子网分配选项和子网信息子选项的DHCPFORCERENEW[RFC3203]消息。收到此消息后，DHCP客户端必须向DHCP服务器发出DHCPREQUEST消息，以便在所述子网上续订租约。分配给客户端的其他子网不受影响。与所有DHCP续订消息的情况一样，客户端可以在子网信息子选项中包含子网使用情况信息，以便报告子网使用情况统计信息，或者如果不报告统计信息，则将“Stat len”字段设置为0。
If the Server responds to this DHCPREQUEST with a DHCPNAK message, then the Client MUST immediately stop using the subnet(s) and, if possible, notify all Clients with addresses allocated from this/these subnet(s) that their addresses are no longer valid. The Client MAY, of course, send a DHCPDISCOVER message containing the Subnet Allocation option and the Subnet-Request suboption in order to acquire another subnet for use.
如果服务器使用DHCPNAK消息响应此DHCPREQUEST，则客户端必须立即停止使用子网，并在可能的情况下，通知从该子网分配地址的所有客户端其地址不再有效。当然，客户端可以发送包含子网分配选项和子网请求子选项的DHCPDISCOVER消息，以便获取另一个子网以供使用。
A DHCP Client MAY request from the DHCP Server a list of what subnets are currently allocated to the Client. This may be used to recover from a restart if the Client does not have local storage in order to retain the information itself. (For an example of this, see Section 8.2 below.)
DHCP客户端可以从DHCP服务器请求当前分配给客户端的子网的列表。如果客户端没有本地存储以保留信息本身，则可以使用此选项从重新启动中恢复。（有关此示例，请参见下文第8.2节。）
The DHCP Client DHCPDISCOVER message, when used to discover already allocated subnet information, SHOULD contain a Subnet-Request suboption with the "Prefix" field set to 0 and with the 'i' flag set to 1 to indicate that the Client is seeking already allocated subnet information from the Server. No Subnet-Information suboptions should be included in this message. Note, no Subnet-Information suboption is included in this message, since the Client would not know of any subnet to request at that point.
DHCP客户端DHCPDISCOVER消息用于发现已分配的子网信息时，应包含一个子网请求子选项，其中“Prefix”字段设置为0，“i”标志设置为1，以指示客户端正在从服务器中查找已分配的子网信息。此消息中不应包含任何子网信息子选项。请注意，此消息中不包含子网信息子选项，因为客户端不知道此时要请求的任何子网。
This DHCPDISCOVER message MAY be unicast to a particular DHCP Server, or broadcast in the normal fashion.
此DHCPDISCOVER消息可以单播到特定的DHCP服务器，或者以正常方式广播。
Any DHCP Server that has allocated subnets to the Client SHOULD respond to the DHCPDISCOVER message with a DHCPOFFER message. The DHCPOFFER message should contain one or more Subnet-Information suboption(s) telling the prefix of the subnet(s) allocated to the Client.
任何已向客户端分配子网的DHCP服务器都应使用DHCPOFFER消息响应DHCPDISCOVER消息。DHCPOFFER消息应包含一个或多个子网信息子选项，告知分配给客户端的子网前缀。
The Server SHOULD, internally, retain an ordered list of subnets that are allocated to each Client. In response to an initial DHCPDISCOVER message requesting allocated subnet information (i.e., one with the 'i' flag set to 1, but not carrying a Subnet-Information suboption), the Server returns in the DHCPOFFER message the subnet information for the first subnet(s) from this list. If the end of the list has been reached, then the 's' bit of the last Subnet-Information suboption included in the message MUST be set to 0. If there are more subnets in the list, the 's' bit MUST be set to 1 to indicate to the Client that more information is available. Since this information is in response to a Client request for previously allocated subnet information, the 'c' bit MUST be set to 1.
服务器应在内部保留分配给每个客户端的子网的有序列表。为了响应请求分配的子网信息的初始DHCPDISCOVER消息（即，“i”标志设置为1但未携带子网信息子选项的消息），服务器在DHCPOFFER消息中返回此列表中第一个子网的子网信息。如果已到达列表末尾，则消息中包含的最后一个子网信息子选项的“s”位必须设置为0。如果列表中有更多子网，“s”位必须设置为1，以向客户端指示有更多可用信息。由于此信息是响应客户端对以前分配的子网信息的请求，“c”位必须设置为1。
The Client, upon receiving any Server DHCPOFFER messages containing Subnet Information suboption information with the 'c' ("Client") bit set, SHOULD gather the network number ("Network") and prefix length ("Prefix") information from the message.
客户端在接收到任何包含子网信息子选项信息且设置了“c”（“客户端”）位的服务器DHCPOFFER消息后，应从消息中收集网络号（“网络”）和前缀长度（“前缀”）信息。
If the 's' bit is set in the last of the Subnet-Information suboptions included in the message, then the Client SHOULD construct a new DHCPDISCOVER message containing the Subnet Allocation option and the last Subnet-Information suboption from the Server's message. This message SHOULD then be sent back to the same DHCP Server originating the DHCPOFFER message. The 'c' and 's' bits MUST retain the same settings they had from the Server's DHCPOFFER message and the network number ("Network") and prefix length ("Prefix") fields MUST be unaltered as well.
如果在消息中包含的最后一个子网信息子选项中设置了“s”位，则客户端应根据服务器的消息构造一条新的DHCPDISCOVER消息，其中包含子网分配选项和最后一个子网信息子选项。然后，应将此消息发送回发起DHCPOFFER消息的同一DHCP服务器。“c”和“s”位必须保留与服务器DHCPOFFER消息中相同的设置，并且网络号（“网络”）和前缀长度（“前缀”）字段也必须不变。
If the 's' bit in all of the Subnet-Information suboptions from the Server was 0, then it indicates the Server has no more information about subnets allocated to the Client.
如果来自服务器的所有子网信息子选项中的“s”位为0，则表示服务器没有关于分配给客户端的子网的更多信息。
The Server, upon receiving from a Client an additional DHCPDISCOVER message for allocated subnet information retrieval, with the 'i' flag set to 1 and containing one or more Subnet Information suboptions with the 'c' and the 's' bits set, MUST use the network number
服务器从客户端接收到用于分配子网信息检索的附加DHCPDISCOVER消息后，如果“i”标志设置为1，并且包含一个或多个子网信息子选项，且设置了“c”和“s”位，则必须使用网络号
("Network") and prefix length ("Prefix") fields contained in the last such Subnet Information suboption. This is in order to locate the position in the internal table of allocated subnets for this Client. Then, the Server MUST return an DHCPOFFER message containing a Subnet-Information suboption giving information about the next set of subnets allocated to this Client. If this finishes the list in the table for this Client, then the 's' bit MUST be set to 0 to indicate there is no more information. Any Subnet Information suboptions encountered without both the 'c' and 's' bits set should be ignored by the Server.
（“网络”）和最后一个子网信息子选项中包含的前缀长度（“前缀”）字段。这是为了在该客户端的已分配子网的内部表中找到位置。然后，服务器必须返回一条DHCPOFFER消息，该消息包含一个子网信息子选项，该子选项提供有关分配给该客户端的下一组子网的信息。如果此操作完成了此客户端表中的列表，则必须将“s”位设置为0，以表示没有更多信息。服务器应忽略未设置“c”和“s”位的任何子网信息子选项。
The actual method of allocating subnets on the DHCP Server, as well as the configuration of what networks may be subnetted and how, is left up to the implementation.
在DHCP服务器上分配子网的实际方法，以及哪些网络可以被子网以及如何被子网的配置，由实现决定。
Only the Subnet Allocation option and accompanying suboptions are displayed in these examples. All other fields in the DHCP messages are described in [RFC2131].
在这些示例中，仅显示子网分配选项和附带的子选项。[RFC2131]中描述了DHCP消息中的所有其他字段。
A DHCP Client requesting a subnet with prefix length 24 from which the Client will allocate addresses to other Clients. The Server responds with an allocation of exactly the size requested:
DHCP客户端请求前缀长度为24的子网，客户端将从该子网向其他客户端分配地址。服务器响应的分配正好是请求的大小：
The Client sends a DHCPDISCOVER message including a Subnet Allocation option with the Subnet-Request suboption:
客户端发送一条DHCPDISCOVER消息，其中包含子网请求子选项的子网分配选项：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 5 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 5 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Server responds with a DHCPOFFER message including a Subnet Allocation option with a Subnet-Information suboption, offering the subnet 10.0.1.0/24.
服务器响应一条DHCPOFFER消息，其中包括一个带有子网信息子选项的子网分配选项，提供子网10.0.1.0/24。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The Client sends a DHCPREQUEST including a Subnet Allocation option with a Subnet-Information suboption:
客户端发送包含子网分配选项和子网信息子选项的DHCPREQUEST：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The Server responds with a DHCPACK message including a Subnet Allocation option with a Subnet-Information suboption:
服务器响应一条DHCPACK消息，其中包含一个带有子网信息子选项的子网分配选项：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
Later, the Client sends a DHCPRELEASE message including a Subnet Allocation option with a Subnet-Information suboption:
稍后，客户机发送一条DHCPRELEASE消息，其中包括一个带有子网信息子选项的子网分配选项：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | 0 |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
A DHCP Client requesting two subnets, each with prefix length 24:
DHCP客户端请求两个子网，每个子网的前缀长度为24：
The Client sends a DHCPDISCOVER message including a Subnet Allocation option with a Subnet-Request suboption:
客户端发送一条DHCPDISCOVER消息，其中包含一个带有子网请求子选项的子网分配选项：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 9 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 9 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 |0|0| 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Server responds with a DHCPOFFER message including a Subnet Allocation option with a Subnet-Information suboption:
服务器响应一条DHCPOFFER消息，其中包含一个带有子网信息子选项的子网分配选项：
The DHCPOFFER specifies one subnet of size 24 and one subnet of size 28.
DHCPOFFER指定一个子网大小为24和一个子网大小为28。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 18 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 15 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 10 | 0 | 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 28 | |0|0| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 18 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 15 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 10 | 0 | 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 28 | |0|0| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Client sends a DHCPREQUEST message including a Subnet Allocation option with a Subnet-Information suboption:
客户端发送一条DHCPREQUEST消息，其中包含一个带有子网信息子选项的子网分配选项：
The Client decides that the subnet of size 28 is not sufficient so it doesn't include that subnet in the DHCPREQUEST message.
客户端决定大小为28的子网不够，因此在DHCPREQUEST消息中不包括该子网。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The Server responds with a DHCPACK message including a Subnet Allocation option with a Subnet-Information suboption:
服务器响应一条DHCPACK消息，其中包含一个带有子网信息子选项的子网分配选项：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
Later, the Client sends a DHCPREQUEST message in order to renew the lease on the one subnet and includes subnet usage information. It reports that a maximum of 10 addresses were allocated from the subnet since the last report, 7 addresses are currently allocated, and 2 addresses were found to be unusable.
稍后，客户端发送DHCPREQUEST消息，以便在一个子网上续订租约，并包括子网使用信息。它报告自上次报告以来，从子网最多分配了10个地址，当前分配了7个地址，发现2个地址不可用。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 17 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 14 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | 0 | 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 17 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 14 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | 0 | 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Server responds with a DHCPACK message; however, it signals to the Client that the subnet should be deprecated.
服务器用DHCPACK消息进行响应；但是，它向客户端发出信号，表示子网应该被弃用。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The Client reloads at this point and, upon completion of the reload, sends a DHCPDISCOVER asking for information about all subnets that were allocated to it.
客户端在此点重新加载，并在完成重新加载后发送DHCPDISCOVER，询问有关分配给它的所有子网的信息。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 5 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | |1|0| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 5 | 0 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | |1|0| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Server responds with a DHCPOFFER, giving the subnet information about the one subnet that is allocated to the Client. Also, the Server specifies that the one allocated subnet should be immediately deprecated. Note that the 's' ("Server") bit is 0, thus indicating that there is no more information available for this Client.
服务器用DHCPOFFERE响应，提供关于分配给客户端的一个子网的子网信息。此外，服务器还指定应立即弃用已分配的子网。请注意，'s'（“服务器”）位为0，因此表示此客户端没有更多可用信息。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |1|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |1|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The Client responds with a DHCPRELEASE message after having deprecated the subnet:
在不推荐使用子网后，客户端将使用DHCPRELEASE消息进行响应：
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | SIS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 220 | 11 | 0 | SIS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | |0|0| 10 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | 0 | 24 | |0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
The following differences may be noticed between Subnet Allocation as described in this document and DHCPv6 Prefix Delegation as described in [RFC3633]:
可能注意到本文档中描述的子网分配与[RFC3633]中描述的DHCPv6前缀委派之间存在以下差异：
o This option does not use anything like an "IA_PD" as is used in DHCPv6.
o 此选项不使用类似于DHCPv6中使用的“IA_PD”的任何内容。
o If the Server cannot allocate a subnet, it remains silent, instead of returning a special response saying nothing is available.
o 如果服务器无法分配子网，它将保持静默，而不是返回一个特殊的响应，说明没有可用的子网。
o DHCPv6 Prefix Delegation has no mechanism for returning subnet/ prefix usage statistics.
o DHCPv6前缀委派没有返回子网/前缀使用统计信息的机制。
o DHCPv6 has no equivalent to the "subnet deprecation" flag as described here.
o DHCPv6没有与此处描述的“子网弃用”标志等效的标志。
o DHCPv6 Prefix Delegation makes no mention of what Client actions should result from receiving a DHCPNAK during a RENEW of a delegation.
o DHCPv6 Prefix Delegation未提及在续订委派期间接收DHCPNAK时应导致哪些客户端操作。
o DHCPv6 has no equivalent of the subnet allocation "Network name" suboption, which may be used by the Server for various purposes, such as to specify a pool to use when allocating a subnet.
o DHCPv6没有子网分配“网络名称”子选项的等效项，服务器可将该子选项用于各种目的，例如指定分配子网时要使用的池。
o DHCPv6 Prefix Delegation corresponds to "Hierarchical Subnet Allocation" (setting the 'h' flag in the Prefix Information block). There is no v6 equivalent of clearing the 'h' flag, in which the Server retains authority over allocation of addresses from the subnet.
o DHCPv6前缀委派对应于“分层子网分配”（在前缀信息块中设置“h”标志）。没有清除“h”标志的v6等价物，在该标志中，服务器保留从子网分配地址的权限。
o DHCPv6 Prefix Delegation has nothing to correspond to the Suggested-Lease-Time suboption.
o DHCPv6前缀委派与建议的租约时间子选项没有对应关系。
Potential exposures to attack are discussed in Section 7 of the DHCP protocol specification [RFC2131]. The Subnet Allocation option can be used to hoard all allocable subnets on a network.
DHCP协议规范[RFC2131]第7节讨论了潜在的攻击风险。子网分配选项可用于存储网络上所有可分配的子网。
Implementations should consider using the DHCP Authentication option [RFC3118] in order to provide a higher level of security if it is deemed necessary in their environment.
实现应该考虑使用DHCP认证选项[RCF31 18]，以便在其环境中被认为必要时提供更高级别的安全性。
IANA has assigned DHCP option number 220 for this option, in accordance with [RFC3942].
IANA已根据[RFC3942]为该选项分配了DHCP选项编号220。
No assignment of values for the suboption codes need be made at this time. New values may only be defined by IETF Consensus, as described in [RFC5226]. Basically, this means that they are defined by RFCs approved by the IESG.
此时无需为子选项代码赋值。如[RFC5226]所述，新值只能由IETF协商一致确定。基本上，这意味着它们由IESG批准的RFC定义。
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119]Bradner，S.，“RFC中用于表示需求水平的关键词”，BCP 14，RFC 2119，1997年3月。
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.
[RFC2131]Droms，R.，“动态主机配置协议”，RFC21311997年3月。
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997.
[RFC2132]Alexander，S.和R.Droms，“DHCP选项和BOOTP供应商扩展”，RFC 21321997年3月。
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003.
[RFC3629]Yergeau，F.，“UTF-8，ISO 10646的转换格式”，STD 63，RFC 3629，2003年11月。
[RFC3942] Volz, B., "Reclassifying Dynamic Host Configuration Protocol version 4 (DHCPv4) Options", RFC 3942, November 2004.
[RFC3942]Volz，B.“重新分类动态主机配置协议版本4（DHCPv4）选项”，RFC 3942，2004年11月。
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC5226]Narten，T.和H.Alvestrand，“在RFCs中编写IANA注意事项部分的指南”，BCP 26，RFC 5226，2008年5月。
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001.
[RFC3118]Droms，R.和W.Arbaugh，“DHCP消息的身份验证”，RFC31182001年6月。
[RFC3203] T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP reconfigure extension", RFC 3203, December 2001.
[RFC3203]T'Joens，Y.，Hublet，C.，和P.De Schrijver，“DHCP重新配置扩展”，RFC32032001年12月。
[RFC3396] Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002.
[RFC3396]Lemon，T.和S.Cheshire，“动态主机配置协议（DHCPv4）中的长选项编码”，RFC 3396，2002年11月。
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.
[RFC3633]Troan，O.和R.Droms，“动态主机配置协议（DHCP）版本6的IPv6前缀选项”，RFC 3633，2003年12月。
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, August 2006.
[RFC4632]Fuller，V.和T.Li，“无类域间路由（CIDR）：互联网地址分配和聚合计划”，BCP 122，RFC 4632，2006年8月。
The authors gratefully acknowledge the contributions of Jay Kumarasamy.
作者衷心感谢Jay Kumarasamy的贡献。
Authors' Addresses
作者地址
Richard A. Johnson Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US
Richard A.Johnson Cisco Systems，Inc.170 W.Tasman Dr.San Jose，CA 95134美国
Phone: +1 408 526 4000
EMail: raj@cisco.com
Phone: +1 408 526 4000
EMail: raj@cisco.com
Kim Kinnear Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US
Kim Kinnear Cisco Systems，Inc.170 W.Tasman Dr.圣何塞，加利福尼亚州，美国95134
Phone: +1 408 526 4000
EMail: kkinnear@cisco.com
Phone: +1 408 526 4000
EMail: kkinnear@cisco.com
Mark Stapp Cisco Systems, Inc. 170 W. Tasman Dr. San Jose, CA 95134 US
Mark Stapp Cisco Systems，Inc.170 W.Tasman Dr.圣何塞，加利福尼亚州，美国95134
Phone: +1 408 526 4000
EMail: mjs@cisco.com
Phone: +1 408 526 4000
EMail: mjs@cisco.com