Network Working Group K. Kinnear
Request for Comments: 5010 M. Normoyle
Category: Standards Track M. Stapp
Cisco Systems, Inc.
September 2007
Network Working Group K. Kinnear
Request for Comments: 5010 M. Normoyle
Category: Standards Track M. Stapp
Cisco Systems, Inc.
September 2007
The Dynamic Host Configuration Protocol Version 4 (DHCPv4) Relay Agent Flags Suboption
动态主机配置协议版本4（DHCPv4）中继代理标记子选项
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。
Abstract
摘要
This memo defines a new suboption of the Dynamic Host Configuration Protocol (DHCP) relay agent information option that allows the DHCP relay to specify flags for the forwarded packet. One flag is defined to indicate whether the DHCP relay received the packet via a unicast or broadcast packet. This information may be used by the DHCP server to better serve clients based on whether their request was originally broadcast or unicast.
此备忘录定义了动态主机配置协议（DHCP）中继代理信息选项的新子选项，该选项允许DHCP中继为转发的数据包指定标志。定义了一个标志来指示DHCP中继是否通过单播或广播数据包接收数据包。该信息可由DHCP服务器用于基于客户端的请求最初是广播还是单播来更好地服务于客户端。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 2
3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 3
4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 3
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . . 5
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 2
3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 3
4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 3
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . . 5
Any time a client's DHCP packet is broadcast, a local DHCP relay will process its request and forward it on to the DHCP server. When the DHCP relay performs this function, it can be configured to use the DHCP relay agent information option to forward additional information to the DHCP server, which the server may then use to alter its processing algorithms. Once the lease has been granted, however, future DHCP DHCPREQUEST/RENEWAL messages are unicast directly to the DHCP Server [RFC2131] [RFC2132] [RFC3046].
每当广播客户端的DHCP数据包时，本地DHCP中继将处理其请求并将其转发到DHCP服务器。当DHCP中继执行此功能时，可以将其配置为使用DHCP中继代理信息选项将附加信息转发给DHCP服务器，然后服务器可以使用这些信息更改其处理算法。但是，一旦授予租约，未来的DHCP DHCPREQUEST/续订消息将直接单播到DHCP服务器[RFC2131][RFC2132][RFC3046]。
In general, DHCP servers may also make subtle (and sometimes not so subtle) changes in their processing algorithms depending on whether or not the DHCP server received the message as a unicast packet from the DHCP client directly, a broadcast packet from the DHCP client on a locally connected network, or a unicast packet from a DHCP Relay Agent, which has forwarded on a packet broadcast from a DHCP client connected to a network local to the DHCP Relay Agent.
通常，DHCP服务器还可以根据DHCP服务器是否直接从DHCP客户端接收作为单播分组的消息、从本地连接网络上的DHCP客户端接收作为广播分组的消息、或从DHCP中继代理接收作为单播分组的消息，对其处理算法进行细微（有时不那么细微）的更改，它通过数据包广播从连接到DHCP中继代理本地网络的DHCP客户端转发。
In some situations, DHCP Clients may unicast their DHCPREQUEST/RENEW packets to the DHCP Relay Agent, which will forward the packet on to the DHCP server. In these cases, the DHCP server cannot tell whether the packet was broadcast or unicast by the DHCP client, and so it may be unable to process the DHCP client packets in the manner that it would if it knew whether the original DHCP packet was broadcast or unicast. For example, a server might be willing to NAK a client in the REBINDING state based on a determination that the client's address does not match its location in the network, but might not be willing to do so if the client is in the RENEWING state.
在某些情况下，DHCP客户端可能将其DHCPREQUEST/RENEW数据包单播到DHCP中继代理，该代理将数据包转发到DHCP服务器。在这些情况下，DHCP服务器无法判断数据包是由DHCP客户端广播还是单播的，因此它可能无法以其知道原始DHCP数据包是广播还是单播的方式处理DHCP客户端数据包。例如，基于确定客户端的地址与其在网络中的位置不匹配，服务器可能愿意在重新绑定状态下NAK客户端，但如果客户端处于续订状态，则可能不愿意这样做。
The purpose of the suboption described in this document is to allow the DHCP relay to specify flags for the forwarded packet. These flags can be used to describe DHCP client attributes that are useful to the DHCP server, but can only be detected by the local DHCP relay. The DHCP server can use the information provided by the DHCP relay to improve its processing algorithms.
本文档中描述的子选项的目的是允许DHCP中继为转发的数据包指定标志。这些标志可用于描述对DHCP服务器有用的DHCP客户端属性，但只能由本地DHCP中继检测。DHCP服务器可以使用DHCP中继提供的信息来改进其处理算法。
One flag is defined to indicate whether the DHCP relay received the packet via a unicast or broadcast packet. This allows the DHCP server to know if a packet forwarded on by a DHCP Relay Agent was broadcast or unicast to the DHCP Relay Agent.
定义了一个标志来指示DHCP中继是否通过单播或广播数据包接收数据包。这允许DHCP服务器知道DHCP中继代理转发的数据包是广播的还是单播到DHCP中继代理的。
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。
The Flags suboption provides an extensible suboption definition for several possible flags. The first flag defined is the unicast flag.
Flags子选项为几个可能的标志提供了一个可扩展的子选项定义。定义的第一个标志是单播标志。
The format of the suboption is:
子选项的格式为：
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code The suboption code (10).
对子选项代码（10）进行编码。
Length The suboption length, 1 octet.
长度子选项长度，1个八位字节。
Flags The Relay Agent flags for this forwarded packet.
标记此转发数据包的中继代理标记。
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|U| MBZ |
+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|U| MBZ |
+-+-+-+-+-+-+-+-+
U: UNICAST flag
U：单播标志
unicast = 1 broadcast = 0
单播=1广播=0
MBZ: MUST BE ZERO (reserved for future use)
MBZ:必须为零（保留供将来使用）
A DHCP relay agent that claims to conform to this specification MUST include this suboption in every Relay Agent Information Option [RFC3046] it adds to a forwarded DHCP request. In this way, the DHCP server can distinguish a request forwarded from a DHCP relay agent that does not support the relay-agent-flags suboption from a request forwarded by a DHCP relay agent that supports the relay-agent-flags suboption, and which received the request that is being forwarded in a broadcast packet.
声称符合此规范的DHCP中继代理必须在其添加到转发的DHCP请求的每个中继代理信息选项[RFC3046]中包含此子选项。通过这种方式，DHCP服务器可以将从不支持中继代理标志子选项的DHCP中继代理转发的请求与由支持中继代理标志子选项的DHCP中继代理转发的请求区分开来，该DHCP中继代理接收到在广播包中转发的请求。
To put this another way, A DHCP relay agent that supports the relay-agent-flags suboption MUST always include it in every relay-agent-information-option that it inserts into packets that it forwards on to the DHCP server, whether the packet it is forwarding was received as a broadcast or as a unicast. This is because the DHCP server will
换句话说，支持中继代理标志子选项的DHCP中继代理必须始终将其包含在每个中继代理信息选项中，该选项插入到它转发到DHCP服务器的数据包中，无论它转发的数据包是作为广播还是作为单播接收的。这是因为DHCP服务器将
be dealing with DHCP relay agents that support the relay-agent-flags suboption as well as DHCP relay agents that do not support the relay-agent-flags suboption.
正在处理支持中继代理标志子选项的DHCP中继代理以及不支持中继代理标志子选项的DHCP中继代理。
This option provides additional information to the DHCP server. The DHCP server MAY use this information to make processing decisions regarding the DHCP Client's packet that it is processing. For instance, knowledge of the broadcast or unicast reception of a packet by a DHCP relay agent could be used when making the processing decisions required to implement Load Balancing [RFC3074]. A load-balancing server may be willing to respond to a REBINDING client, but the server cannot determine the client's state without this additional indication.
此选项向DHCP服务器提供附加信息。DHCP服务器可以使用该信息来作出关于其正在处理的DHCP客户端的数据包的处理决定。例如，当做出实现负载平衡所需的处理决策时，可以使用DHCP中继代理对分组的广播或单播接收的知识[RFC3074]。负载平衡服务器可能愿意响应重新绑定的客户端，但如果没有此附加指示，服务器无法确定客户端的状态。
The option length is one octet. If the DHCP server receives a relay-agent-flags suboption that is longer than one octet, it MUST evaluate the first octet.
选项长度为一个八位字节。如果DHCP服务器收到的中继代理标志子选项长于一个八位字节，则必须计算第一个八位字节。
Note to implementors: In specifying the behavior of new flags bits in the future, careful attention must be paid to compatibility with earlier implementations. If additional flags values are defined in the future, it will not always be possible to distinguish between messages from relay agents who understand the new value and set its value to 'zero', and relay agents who are simply setting a series of unassigned bits to 'zero'. It would be a mistake to specify significant behavior changes based on 'zero' values of flags specified in the future.
Note to implementors: In specifying the behavior of new flags bits in the future, careful attention must be paid to compatibility with earlier implementations. If additional flags values are defined in the future, it will not always be possible to distinguish between messages from relay agents who understand the new value and set its value to 'zero', and relay agents who are simply setting a series of unassigned bits to 'zero'. It would be a mistake to specify significant behavior changes based on 'zero' values of flags specified in the future.translate error, please retry
Message authentication in DHCP for intradomain use, where the out-of-band exchange of a shared secret is feasible, is defined in [RFC3118]. Potential exposures to attack are discussed in Section 7 of the DHCP protocol specification in [RFC2131].
[RFC3118]中定义了用于域内使用的DHCP中的消息身份验证，其中共享秘密的带外交换是可行的。[RFC2131]中DHCP协议规范的第7节讨论了潜在的攻击风险。
The DHCP Relay Agent option depends on a trusted relationship between the DHCP relay agent and the server, as described in Section 5 of [RFC3046]. While the introduction of fraudulent relay-agent options can be prevented by a perimeter defense that blocks these options unless the relay agent is trusted, a deeper defense using the authentication option for relay agent options [RFC4030] SHOULD be deployed as well.
DHCP中继代理选项取决于DHCP中继代理和服务器之间的信任关系，如[RFC3046]第5节所述。虽然引入欺诈性中继代理选项可以通过周界防御来防止，除非中继代理受信任，否则周界防御会阻止这些选项，但也应该部署使用中继代理选项的身份验证选项[RFC4030]的更深入防御。
IANA has assigned a suboption number (10) for the Flags Suboption from the DHCP Relay Agent Information Option [RFC3046] suboption number space.
IANA已从DHCP中继代理信息选项[RFC3046]子选项编号空间为标志子选项分配了子选项编号（10）。
Thanks to David Hankins for realizing the problems created by the server-id-override option document and for helping us understand the value of finally solving this problem in a way that has general applicability.
感谢David Hankins认识到服务器id覆盖选项文档所产生的问题，并帮助我们理解最终以具有普遍适用性的方式解决此问题的价值。
[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。
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001.
[RFC3046]Patrick，M.，“DHCP中继代理信息选项”，RFC3046，2001年1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。
[RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option", RFC 4030, March 2005.
[RFC4030]Stapp，M.和T.Lemon，“动态主机配置协议（DHCP）中继代理选项的身份验证子选项”，RFC 4030，2005年3月。
[RFC3074] Volz, B., Gonczi, S., Lemon, T., and R. Stevens, "DHC Load Balancing Algorithm", RFC 3074, February 2001.
[RFC3074]Volz，B.，Gonczi，S.，Lemon，T.，和R.Stevens，“DHC负载平衡算法”，RFC 3074，2001年2月。
Authors' Addresses
作者地址
Kim Kinnear Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 US
Kim Kinnear Cisco Systems，Inc.美国马萨诸塞州Boxborough大道1414号，邮编01719
Phone: +1 978 936 0000
EMail: kkinnear@cisco.com
Phone: +1 978 936 0000
EMail: kkinnear@cisco.com
Marie Normoyle Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 US
美国马萨诸塞州伯斯堡马萨诸塞大道1414号玛丽·诺莫耶思科系统公司，邮编01719
Phone: +1 978 936 0000
EMail: mnormoyle@cisco.com
Phone: +1 978 936 0000
EMail: mnormoyle@cisco.com
Mark Stapp Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 US
美国马萨诸塞州伯斯堡马萨诸塞大道1414号Mark Stapp Cisco Systems，Inc.01719
Phone: +1 978 936 0000
EMail: mjs@cisco.com
Phone: +1 978 936 0000
EMail: mjs@cisco.com
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