Internet Engineering Task Force (IETF)                          A. DeKok
Request for Comments: 8559                                    FreeRADIUS
Updates: 5176, 5580                                          J. Korhonen
Category: Standards Track                                     April 2019
ISSN: 2070-1721
Internet Engineering Task Force (IETF)                          A. DeKok
Request for Comments: 8559                                    FreeRADIUS
Updates: 5176, 5580                                          J. Korhonen
Category: Standards Track                                     April 2019
ISSN: 2070-1721

Dynamic Authorization Proxying in the Remote Authentication Dial-In User Service (RADIUS) Protocol




RFC 5176 defines Change-of-Authorization (CoA) and Disconnect Message (DM) behavior for RADIUS. RFC 5176 also suggests that proxying these messages is possible, but it does not provide guidance as to how that is done. This specification updates RFC 5176 to correct that omission for scenarios where networks use realm-based proxying as defined in RFC 7542. This specification also updates RFC 5580 to allow the Operator-Name attribute in CoA-Request and Disconnect-Request packets.

RFC 5176定义RADIUS的授权变更(CoA)和断开消息(DM)行为。RFC 5176还建议代理这些消息是可能的,但它没有提供如何执行的指导。本规范更新了RFC 5176,以纠正网络使用RFC 7542中定义的基于领域的代理的情况下的遗漏。本规范还更新了RFC 5580,以允许CoA请求和断开请求数据包中的操作员名称属性。

Status of This Memo


This is an Internet Standards Track document.


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). Further information on Internet Standards is available in Section 2 of RFC 7841.

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。有关互联网标准的更多信息,请参见RFC 7841第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

版权(c)2019 IETF信托基金和被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 ( 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(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。

Table of Contents


   1. Introduction ....................................................3
      1.1. Terminology ................................................4
      1.2. Requirements Language ......................................5
   2. Problem Statement ...............................................5
      2.1. Typical RADIUS Proxying ....................................5
      2.2. CoA Processing .............................................6
      2.3. Failure of CoA Proxying ....................................6
   3. How to Perform CoA Proxying .....................................7
      3.1. Changes to Access-Request and Accounting-Request Packets ...8
      3.2. Proxying of CoA-Request and Disconnect-Request Packets .....9
      3.3. Reception of CoA-Request and Disconnect-Request Packets ...10
      3.4. Operator-NAS-Identifier ...................................11
   4. Requirements ...................................................14
      4.1. Requirements on Home Servers ..............................14
      4.2. Requirements on Visited Networks ..........................14
      4.3. Requirements on Proxies ...................................14
           4.3.1. Security Requirements on Proxies ...................15
           4.3.2. Filtering Requirements on Proxies ..................16
   5. Functionality ..................................................17
      5.1. User Login ................................................17
      5.2. CoA Proxying ..............................................17
   6. Security Considerations ........................................18
      6.1. RADIUS Security and Proxies ...............................18
      6.2. Security of the Operator-NAS-Identifier Attribute .........19
   7. IANA Considerations ............................................20
   8. References .....................................................20
      8.1. Normative References ......................................20
      8.2. Informative References ....................................21
   Authors' Addresses ................................................21
   1. Introduction ....................................................3
      1.1. Terminology ................................................4
      1.2. Requirements Language ......................................5
   2. Problem Statement ...............................................5
      2.1. Typical RADIUS Proxying ....................................5
      2.2. CoA Processing .............................................6
      2.3. Failure of CoA Proxying ....................................6
   3. How to Perform CoA Proxying .....................................7
      3.1. Changes to Access-Request and Accounting-Request Packets ...8
      3.2. Proxying of CoA-Request and Disconnect-Request Packets .....9
      3.3. Reception of CoA-Request and Disconnect-Request Packets ...10
      3.4. Operator-NAS-Identifier ...................................11
   4. Requirements ...................................................14
      4.1. Requirements on Home Servers ..............................14
      4.2. Requirements on Visited Networks ..........................14
      4.3. Requirements on Proxies ...................................14
           4.3.1. Security Requirements on Proxies ...................15
           4.3.2. Filtering Requirements on Proxies ..................16
   5. Functionality ..................................................17
      5.1. User Login ................................................17
      5.2. CoA Proxying ..............................................17
   6. Security Considerations ........................................18
      6.1. RADIUS Security and Proxies ...............................18
      6.2. Security of the Operator-NAS-Identifier Attribute .........19
   7. IANA Considerations ............................................20
   8. References .....................................................20
      8.1. Normative References ......................................20
      8.2. Informative References ....................................21
   Authors' Addresses ................................................21
1. Introduction
1. 介绍

RFC 5176 [RFC5176] defines Change-of-Authorization (CoA) and Disconnect Message (DM) behavior for RADIUS. Section 3.1 of [RFC5176] suggests that proxying these messages is possible, but it does not provide guidance as to how that is done. This omission means that in practice, proxying of CoA packets is impossible.

RFC 5176[RFC5176]定义RADIUS的授权变更(CoA)和断开消息(DM)行为。[RFC5176]第3.1节建议代理这些消息是可能的,但它没有提供如何进行的指导。这种省略意味着在实践中,CoA数据包的代理是不可能的。

We partially correct that omission here by explaining how proxying of these packets can be done by leveraging an existing RADIUS attribute, Operator-Name (Section 4.1 of [RFC5580]). We then explain how this attribute can be used by proxies to route packets "backwards" through a RADIUS proxy chain from a home network to a visited network. We then introduce a new attribute: Operator-NAS-Identifier. This attribute permits packets to be routed from the RADIUS server at the visited network to the Network Access Server (NAS).


This correction is limited to the use case of realm-based proxying as defined in [RFC7542]. Other forms of proxying are possible but are not discussed here. We note that the recommendations provided in this document apply only to those systems that implement proxying of CoA packets, and then only to those that implement realm-based CoA proxying. This specification neither requires nor suggests changes to any implementation or deployment of any other RADIUS systems.


We also update the behavior described in [RFC5580] to allow the Operator-Name attribute to be used in CoA-Request and Disconnect-Request packets, as further described in this document.

我们还更新了[RFC5580]中描述的行为,以允许在CoA请求和断开连接请求数据包中使用Operator Name属性,如本文档中所述。

This document is a Standards Track document in order to update the behavior described in [RFC5580], as [RFC5580] is also a Standards Track document. This document relies heavily upon and also updates some of the behaviors described in RFC 5176, which is an Informational document; because the applicability statements in Section 1.1 of [RFC5176] do not apply to this document, this document does not change the status of [RFC5176].

本文件为标准跟踪文件,用于更新[RFC5580]中描述的行为,因为[RFC5580]也是标准跟踪文件。本文件高度依赖并更新了RFC 5176中描述的一些行为,RFC 5176是一份信息性文件;由于[RFC5176]第1.1节中的适用性声明不适用于本文件,因此本文件不会更改[RFC5176]的状态。

We finally conclude with a discussion of the security implications of this design and show that they do not decrease the security of the network.


1.1. Terminology
1.1. 术语

This document frequently uses the following terms:




Change of authorization, e.g., CoA-Request, CoA-ACK, or CoA-NAK, as defined in [RFC5176]. [RFC5176] also defines Disconnect-Request, Disconnect-ACK, and Disconnect-NAK. For simplicity, where we use "CoA" in this document, we mean a generic "CoA-Request or Disconnect-Request" packet. We use "CoA-Request" or "Disconnect-Request" to refer to the specific packet types.

授权变更,如[RFC5176]中定义的CoA请求、CoA确认或CoA NAK。[RFC5176]还定义了断开请求、断开确认和断开NAK。为简单起见,在本文档中使用“CoA”时,我们指的是通用的“CoA请求或断开连接请求”数据包。我们使用“CoA请求”或“断开连接请求”来表示特定的数据包类型。

Network Access Identifier (NAI)


The user identity submitted by the client during network access authentication. See [RFC7542]. The purpose of the NAI is to identify the user as well as assist in the routing of the authentication request. Please note that the NAI may not necessarily be the same as the user's email address or the user identity submitted in an application-layer authentication.


Network Access Server (NAS)


The device that clients connect to in order to get access to the network. In Point-to-Point Tunneling Protocol (PPTP) terminology, this is referred to as the PPTP Access Concentrator (PAC), and in Layer 2 Tunneling Protocol (L2TP) terminology, it is referred to as the L2TP Access Concentrator (LAC). In IEEE 802.11, it is referred to as an Access Point.

客户端为了访问网络而连接到的设备。在点对点隧道协议(PPTP)术语中,这称为PPTP访问集中器(PAC),在第二层隧道协议(L2TP)术语中,这称为L2TP访问集中器(LAC)。在IEEE 802.11中,它被称为接入点。

Home Network


The network that holds the authentication credentials for a user.


Visited Network


A network other than the home network, where the user attempts to gain network access. The visited network typically has a relationship with the home network, possibly through one or more intermediary proxies.


1.2. Requirements Language
1.2. 需求语言

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“建议”、“不建议”、“可”和“可选”在所有大写字母出现时(如图所示)应按照BCP 14[RFC2119][RFC8174]所述进行解释。

2. Problem Statement
2. 问题陈述

This section describes how RADIUS proxying works, how CoA packets work, and why CoA proxying as discussed in [RFC5176] is insufficient to create a working system.


2.1. Typical RADIUS Proxying
2.1. 典型半径代理

When a RADIUS server proxies an Access-Request packet, it typically does so based on the contents of the User-Name attribute, which contains an NAI [RFC7542]. This specification describes how to use the NAI in order to proxy CoA packets across multiple hops. Other methods of proxying CoA packets are possible but are not discussed here.


In order to determine the "next hop" for a packet, the proxying server looks up the "realm" portion of the NAI in a logical Authentication, Authorization, and Accounting (AAA) routing table, as described in Section 3 of [RFC7542]. The entry in that table contains information about the next hop to which the packet is sent. This information can be IP address, shared secret, certificate, etc. The next hop may also be another proxy, or it may be the home server for that realm.


If the next hop is a proxy, that proxy will perform the same realm lookup and then proxy the packet as above. At some point, the next hop will be the home server for that realm.


The home server validates the NAI in the User-Name attribute against the list of realms hosted by the home network. If there is no match, then an Access-Reject is returned. All other packets are processed through local site rules, which result in an appropriate response packet being sent. This response packet can be Access-Accept, Access-Challenge, or Access-Reject.


The RADIUS client receiving that response packet will match it to an outstanding request. If the client is part of a proxy, the proxy will then send that response packet in turn to the system that originated the Access-Request. This process continues until the response packet arrives at the NAS.


The proxies are typically stateful with respect to ongoing request/response packets but are stateless with respect to user sessions. That is, once a response has been sent by the proxy, it can discard all information about the request packet, other than what is needed for detecting retransmissions as per Section 2.2.2 of [RFC5080].


The same method is used to proxy Accounting-Request packets. Proxying both Access-Request and Accounting-Request packets allows proxies to connect visited networks to home networks for all AAA purposes.


2.2. CoA Processing
2.2. 辅酶A处理

[RFC5176] describes how CoA clients send packets to CoA servers. We note that a system comprising the CoA client is typically co-located with, or is the same as, the RADIUS server. Similarly, the CoA server is a system that is either co-located with or the same as the RADIUS client.


In the case of packets sent inside of one network, the source and destination of CoA packets are locally determined. There is thus no need for standardization of that process, as networks are free to send CoA packets whenever they want, for whatever reason they want.


2.3. Failure of CoA Proxying
2.3. CoA代理失效

The situation is more complicated when proxies are involved. [RFC5176] suggests that CoA proxying is permitted, but [RFC5176] does not make any suggestions as to how that proxying should be done.


If proxies were to track user sessions, it would be possible for a proxy to match an incoming CoA packet to a user session and then to proxy the CoA packet to the RADIUS client that originated the Access-Request for that session. There are many problems with such a scenario.


The CoA server might not, in fact, be co-located with the RADIUS client, in which case it might not have access to user session information for performing the reverse path forwarding.


The CoA server may be down, but there may be a different CoA server that could successfully process the packet. The CoA client should then fail over to a different CoA server. If the reverse path is restricted to be the same as the forward path, then such failover is not possible.


In a roaming consortium, the proxies may forward traffic for tens of millions of users. Tracking each user session can be expensive and complicated, and doing so does not scale well. For that reason, most proxies do not record user sessions.


Even if the proxy recorded user sessions, [RFC5176] is silent on the topic of what attributes constitute "session identification attributes". That silence means it is impossible for a proxy to determine if a CoA packet matches a particular user session.


The result of all of these issues is that CoA proxying is impossible when using the behavior defined in [RFC5176].


3. How to Perform CoA Proxying
3. 如何执行CoA代理

The solution to the above problem is to use realm-based proxying on the reverse path, just as with the forward path. In order for the reverse path proxying to work, the proxy decision must be based on an attribute other than User-Name.


The reverse path proxying can be done by using the Operator-Name attribute defined in Section 4.1 of [RFC5580]. We repeat a portion of that definition here for clarity:


This attribute carries the operator namespace identifier and the operator name. The operator name is combined with the namespace identifier to uniquely identify the owner of an access network.


...followed a few paragraphs later by a description of the REALM namespace:


REALM ('1' (0x31)):


The REALM operator namespace can be used to indicate operator names based on any registered domain name. Such names are required to be unique, and the rights to use a given realm name are obtained coincident with acquiring the rights to use a particular Fully Qualified Domain Name (FQDN). ...


In short, the Operator-Name attribute contains an ASCII "1", followed by the realm of the visited network. For example, for the "" realm, the Operator-Name attribute contains the text "". This information is precisely what is needed by intermediate nodes in order to perform CoA proxying.

简而言之,Operator Name属性包含一个ASCII“1”,后跟访问网络的域。例如,对于“”领域,Operator Name属性包含文本“”。此信息正是中间节点执行CoA代理所需的信息。

The remainder of this document describes how CoA proxying can be performed by using the Operator-Name attribute. We describe the following:


o how the forward path has to change in order to allow reverse path proxying

o 如何更改正向路径以允许反向路径代理

o how reverse path proxying works

o 反向路径代理的工作原理

o how visited networks and home networks have to behave in order for CoA proxying to work

o 访问网络和家庭网络必须如何运行才能使代理工作

We note that as a proxied CoA packet is sent to only one destination, the Operator-Name attribute MUST NOT occur more than once in a packet. If a packet contains more than one Operator-Name, implementations MUST treat the second and subsequent attributes as "invalid attributes", as discussed in Section 2.8 of [RFC6929].


3.1. Changes to Access-Request and Accounting-Request Packets
3.1. 访问请求和记帐请求数据包的更改

When a visited network proxies an Access-Request or Accounting-Request packet outside of its network, a visited network that wishes to support realm-based CoA proxying SHOULD include an Operator-Name attribute in the packet, as discussed in Section 4.1 of [RFC5580]. The contents of the Operator-Name attribute should be "1", followed by the realm name of the visited network. Where the visited network has more than one realm name, a "canonical" name SHOULD be chosen and used for all packets.

当到访网络在其网络之外代理访问请求或记帐请求数据包时,希望支持基于领域的代理的到访网络应在数据包中包含操作员名称属性,如[RFC5580]第4.1节所述。Operator Name属性的内容应为“1”,后跟访问网络的域名。如果访问的网络有多个域名,则应选择一个“规范”名称并用于所有数据包。

Visited networks MUST use a consistent value for Operator-Name for any one user session. That is, sending "" in an Access-Request packet and "" in an Accounting-Request packet for that same session is forbidden. Such behavior would make it look like a single user session was active simultaneously in two different visited networks, which is impossible.


Proxies that record user session information SHOULD also record Operator-Name. Proxies that do not record user session information do not need to record Operator-Name.


Home networks SHOULD record Operator-Name along with any other information that they record about user sessions. Home networks that expect to send CoA packets to visited networks MUST record Operator-Name for each user session that originates from a visited network. Failure to record Operator-Name would mean that the home network would not know where to send any CoA packets.


Networks that host both the RADIUS client and RADIUS server do not need to create, record, or track Operator-Name. That is, if the visited network and home network are the same, there is no need to use the Operator-Name attribute.


3.2. Proxying of CoA-Request and Disconnect-Request Packets
3.2. 代理CoA请求和断开连接请求数据包

When a home network wishes to send a CoA-Request or Disconnect-Request packet to a visited network, it MUST include an Operator-Name attribute in the CoA packet. The value of the Operator-Name attribute MUST be the value that was recorded earlier for that user session.

当家庭网络希望向到访网络发送CoA请求或断开请求数据包时,必须在CoA数据包中包含操作员名称属性。Operator Name属性的值必须是先前为该用户会话记录的值。

The home network MUST look up the realm from the Operator-Name attribute in a logical "realm routing table", as discussed in Section 3 of [RFC7542]. That logical realm table is defined therein as:


... a logical AAA routing table, where the "utf8-realm" portion acts as a key, and the values stored in the table are one or more "next hop" AAA servers.

... 逻辑AAA路由表,其中“utf8领域”部分用作密钥,表中存储的值是一个或多个“下一跳”AAA服务器。

In order to support proxying of CoA packets, this table is extended to include a mapping between "utf8-realm" and one or more next-hop CoA servers.


When proxying CoA-Request and Disconnect-Request packets, the lookups will return data from the "CoA server" field instead of the "AAA server" field.


In practice, this process means that CoA proxying works exactly like "normal" RADIUS proxying, except that the proxy decision is made using the realm from the Operator-Name attribute instead of using the realm from the User-Name attribute.

实际上,此过程意味着CoA代理的工作方式与“正常”半径代理的工作方式完全相同,只是代理决策是使用Operator Name属性中的领域而不是使用User Name属性中的领域做出的。

Proxies that receive the CoA packet will look up the realm from the Operator-Name attribute in a logical "realm routing table", as with home servers, above. The packet is then sent to the proxy for the realm that was found in that table. This process continues with any subsequent proxies until the packet reaches a public CoA server at the visited network.

接收CoA数据包的代理将从逻辑“领域路由表”中的Operator Name属性查找领域,与上面的家庭服务器一样。然后将数据包发送到该表中找到的领域的代理。此过程继续与任何后续代理一起进行,直到数据包到达访问网络的公共CoA服务器。

Where the realm is unknown, the proxy MUST return a NAK packet that contains an Error-Cause Attribute having value 502 ("Request Not Routable").


Proxies that receive a CoA packet MUST NOT use the NAI from the User-Name attribute in order to make proxying decisions. Doing so would result in the CoA packet being forwarded to the home network, while the user's session is in the visited network.


We also update Section 5 of [RFC5580] to permit CoA-Request and Disconnect-Request packets to contain zero or one instance of the Operator-Name attribute.


3.3. Reception of CoA-Request and Disconnect-Request Packets
3.3. 接收CoA请求和断开连接请求数据包

After some proxying, the CoA packet will be received by the CoA server in the visited network. That CoA server MUST validate the NAI in the Operator-Name attribute against the list of realms hosted by the visited network. If the realm is not found, then the CoA server MUST return a NAK packet that contains an Error-Cause Attribute having value 502 ("Request Not Routable").

在一些代理之后,访问网络中的CoA服务器将接收CoA数据包。CoA服务器必须根据访问网络托管的领域列表验证Operator Name属性中的NAI。如果未找到域,则CoA服务器必须返回一个NAK数据包,该数据包包含一个值为502的错误原因属性(“请求不可路由”)。

Some home networks will not have permission to send CoA packets to the visited network. The CoA server SHOULD therefore also validate the NAI contained in the User-Name attribute. If the home network is not permitted to send CoA packets to this visited network, then the CoA server MUST return a NAK packet that contains an Error-Cause Attribute having value 502 ("Request Not Routable").


These checks make it more difficult for a malicious home network to scan roaming networks in order to determine which visited network hosts which realm. That information should be known to all parties in advance and exchanged via methods outside the scope of this specification. Those methods will typically be in the form of contractual relationships between parties or membership in a roaming consortium.


The CoA server in the visited network will also ensure that the Operator-NAS-Identifier attribute is known, as described below. If the attribute matches a known NAS, then the packet will be sent to that NAS. Otherwise, the CoA server MUST return a NAK packet that contains an Error-Cause Attribute having value 403 ("NAS Identification Mismatch").


All other received packets are processed as per local site rules and will result in an appropriate response packet being sent. This process mirrors the method used to process Access-Request and Accounting-Request packets (described above).


Processing done by the visited network will normally include sending the CoA packet to the NAS, having the NAS process it, and then returning any response packets back up the proxy chain to the home server.


The only missing piece here is the procedure by which the visited network gets the packet from its public CoA server to the NAS. The visited network could use NAS-Identifier, NAS-IP-Address, or NAS-IPv6-Address, but these attributes may have been edited by an intermediate proxy or the attributes may be missing entirely.

这里唯一缺少的是访问网络从其公共CoA服务器获取数据包到NAS的过程。访问的网络可以使用NAS标识符、NAS IP地址或NAS-IPv6-Address,但这些属性可能已由中间代理编辑,或者这些属性可能完全丢失。

These attributes may be incorrect because proxies forwarding Access-Request packets often rewrite them for internal policy reasons. These attributes may be missing, because the visited network may not want all upstream proxies and home servers to have detailed information about the internals of its private network and may remove them itself.


We therefore need a way to identify a NAS in the visited network via a method that affords privacy and does not use any existing attributes. Our solution is to define an Operator-NAS-Identifier attribute, which identifies an individual NAS in the visited network.


3.4. Operator-NAS-Identifier
3.4. 操作员NAS标识符

The Operator-NAS-Identifier attribute is an opaque token that identifies an individual NAS in a visited network. It MAY appear in the following packets: Access-Request, Accounting-Request, CoA-Request, or Disconnect-Request. Operator-NAS-Identifier MUST NOT appear in any other packets.

Operator NAS Identifier属性是一个不透明令牌,用于标识访问网络中的单个NAS。它可能出现在以下数据包中:访问请求、记帐请求、CoA请求或断开连接请求。操作员NAS标识符不得出现在任何其他数据包中。

Operator-NAS-Identifier MAY occur in a packet if the packet also contains an Operator-Name attribute. Operator-NAS-Identifier MUST NOT appear in a packet if there is no Operator-Name in the packet. As each proxied CoA packet is sent to only one NAS, the Operator-NAS-Identifier attribute MUST NOT occur more than once in a packet. If a packet contains more than one Operator-NAS-Identifier, implementations MUST treat the second and subsequent attributes as "invalid attributes", as discussed in Section 2.8 of [RFC6929].


An Operator-NAS-Identifier attribute SHOULD be added to an Access-Request or Accounting-Request packet by a visited network, before proxying a packet to an external RADIUS server. When the Operator-NAS-Identifier attribute is added to a packet, the following attributes SHOULD be deleted from the packet: NAS-IP-Address, NAS-IPv6-Address, and NAS-Identifier. If these attributes are deleted, the proxy MUST then add a new NAS-Identifier attribute,

在将数据包代理到外部RADIUS服务器之前,应通过访问的网络将操作员NAS标识符属性添加到访问请求或记帐请求数据包中。将操作员NAS标识符属性添加到数据包时,应从数据包中删除以下属性:NAS IP地址、NAS-IPv6-Address和NAS标识符。如果删除了这些属性,则代理必须添加新的NAS标识符属性,

in order to satisfy the requirements of Section 4.1 of [RFC2865] and Section 4.1 of [RFC2866]. The contents of the new NAS-Identifier attribute SHOULD be the realm name of the visited network.


When a server receives a packet that already contains an Operator-NAS-Identifier attribute, no such editing is performed.


The Operator-NAS-Identifier attribute MUST NOT be added to any packet by any other proxy or server in the network. Only the visited network (i.e., the operator) can name a NAS that is inside of the visited network.


The result of these requirements is that for everyone outside of the visited network there is only one NAS: the visited network itself. Also, the visited network is able to identify its own NASes to its own satisfaction.


This usage of the Operator-NAS-Identifier attribute parallels the Operator-Name attribute as defined in Section 4.1 of [RFC5580].


The Operator-NAS-Identifier attribute is defined as follows.




An opaque token describing the NAS a user has logged into.




241.8 (assigned by IANA from the "short extended space" [RFC6929] of the "RADIUS Attribute Types" registry).



4 to 35.


Implementations supporting this attribute MUST be able to handle between one (1) and thirty-two (32) octets of data. Implementations creating an Operator-NAS-Identifier attribute MUST NOT create attributes with more than sixty-four (64) octets of data. A 32-octet string should be more than sufficient for future uses.


Data Type


The data type of this field is "string". See Section 3.5 of [RFC8044] for a definition.




This attribute contains an opaque token that can only be interpreted by the visited network.


This token MUST allow the visited network to direct the packet to the NAS for the user's session. In practice, this requirement means that the visited network has two practical methods for creating the value.


The first method is to create an opaque token per NAS and then to store that information in a database. The database can be configured to allow querying by NAS IP address in order to find the correct Operator-NAS-Identifier. The database can also be configured to allow querying by Operator-NAS-Identifier in order to find the correct NAS IP address.

第一种方法是为每个NAS创建不透明令牌,然后将该信息存储在数据库中。数据库可以配置为允许通过NAS IP地址进行查询,以便找到正确的操作员NAS标识符。还可以将数据库配置为允许通过操作员NAS标识符进行查询,以找到正确的NAS IP地址。

The second method is to obfuscate the NAS IP address using information known locally by the visited network -- for example, by XORing it with a locally known secret key. The output of that obfuscation operation is data that can be used as the value of Operator-NAS-Identifier. On reception of a CoA packet, the locally known information can be used to unobfuscate the value of Operator-NAS-Identifier, in order to determine the actual NAS IP address.

第二种方法是使用访问的网络本地已知的信息混淆NAS IP地址,例如,使用本地已知的密钥对其进行XORing。该混淆操作的输出是可以用作操作员NAS标识符值的数据。在接收到CoA数据包时,本地已知信息可用于解模糊操作员NAS标识符的值,以确定实际NAS IP地址。

Note that there is no requirement that the value of Operator-NAS-Identifier be checked for integrity. Modification of the value can only result in the erroneous transaction being rejected.


We note that the Access-Request and Accounting-Request packets often contain the Media Access Control (MAC) address of the NAS. There is therefore no requirement that Operator-NAS-Identifier obfuscate or hide in any way the total number of NASes in a visited network. That information is already public knowledge.


4. Requirements
4. 要求
4.1. Requirements on Home Servers
4.1. 对家庭服务器的要求

The Operator-NAS-Identifier attribute MUST be stored by a home server along with any user session identification attributes. When sending a CoA packet for a user session, the home server MUST include verbatim any Operator-NAS-Identifier it has recorded for that session.


A home server MUST NOT send CoA packets for users of other networks. The next few sections describe how other participants in the RADIUS ecosystem can help enforce this requirement.


4.2. Requirements on Visited Networks
4.2. 访问网络的要求

A visited network that receives a CoA packet that will be proxied to a NAS MUST perform all of the operations required for proxies; see Section 4.3.2. We specify this requirement because we assume that the visited network has a proxy between the NAS and any external (i.e., third-party) proxy. Situations where a NAS sends packets directly to a third-party RADIUS server are outside the scope of this specification.


The visited network uses the contents of the Operator-NAS-Identifier attribute to determine which NAS will receive the packet.


The visited network MUST remove the Operator-Name and Operator-NAS-Identifier attributes from a given CoA packet prior to sending that packet to the final CoA server (i.e., NAS). This step is necessary due to the limits specified in Section 2.3 of [RFC5176].


The visited network MUST also ensure that the CoA packet sent to the NAS contains one of the following attributes: NAS-IP-Address, NAS-IPv6-Address, or NAS-Identifier. This step is the inverse of the removal suggested above in Section 3.4.

访问的网络还必须确保发送到NAS的CoA数据包包含以下属性之一:NAS IP地址、NAS-IPv6-Address或NAS标识符。该步骤与上文第3.4节中建议的移除相反。

In general, the NAS should only receive attributes that identify or modify a user's session. It is not appropriate to send to a NAS attributes that are used only for inter-proxy signaling.


4.3. Requirements on Proxies
4.3. 对代理人的要求

There are a number of requirements on both CoA proxies and RADIUS proxies. For the purpose of this section, we assume that each RADIUS proxy shares a common administration with a corresponding CoA proxy and that the two systems can communicate electronically. There is no requirement that these systems be co-located.


4.3.1. Security Requirements on Proxies
4.3.1. 代理的安全要求

Section 6.1 of [RFC5176] has some security requirements on proxies that handle CoA-Request and Disconnect-Request packets:


... a proxy MAY perform a "reverse path forwarding" (RPF) check to verify that a Disconnect-Request or CoA-Request originates from an authorized Dynamic Authorization Client.

... 代理可以执行“反向路径转发”(RPF)检查,以验证断开连接请求或CoA请求是否源自授权的动态授权客户端。

We strengthen that requirement by saying that a proxy MUST perform a reverse path forwarding check to verify that a CoA packet originates from an authorized Dynamic Authorization Client. Without this check, a proxy may forward packets from misconfigured or malicious parties and thus contribute to the problem instead of preventing it. Where the check fails, the proxy MUST return a NAK packet that contains an Error-Cause Attribute having value 502 ("Request Not Routable").


Proxies that record user session information SHOULD verify the contents of a received CoA packet against the recorded data for that user session. If the proxy determines that the information in the packet does not match the recorded user session, it SHOULD return a NAK packet that contains an Error-Cause Attribute having value 503 ("Session Context Not Found"). These checks cannot be mandated due to the fact that [RFC5176] offers no advice on which attributes are used to identify a user's session.


Because a RADIUS proxy will see Access-Request and Accounting-Request packets, we recognize that it will have sufficient information to forge CoA packets. The RADIUS proxy will thus have the ability to subsequently disconnect any user who was authenticated through itself.


We suggest that the real-world effect of this security problem is minimal. RADIUS proxies can already return Access-Accept or Access-Reject for Access-Request packets and can change authorization attributes contained in an Access-Accept. Allowing a proxy to change (or disconnect) a user session post-authentication is not substantially different from changing (or refusing to connect) a user session during the initial process of authentication.


The biggest problem is that there are no provisions in RADIUS for "end-to-end" security. That is, the visited network and home network cannot communicate privately in the presence of proxies. This limitation originates from the design of RADIUS for Access-Request and Accounting-Request packets. That limitation is then carried over to CoA-Request and Disconnect-Request packets.


We therefore cannot prevent proxies or home servers from forging CoA packets. We can only create scenarios where that forgery is hard to perform, is likely to be detected, and/or has no effect.


4.3.2. Filtering Requirements on Proxies
4.3.2. 代理的过滤要求

Section 2.3 of [RFC5176] makes the following requirement for CoA servers:


In CoA-Request and Disconnect-Request packets, all attributes MUST be treated as mandatory.


This requirement is too stringent for a CoA proxy. Only the final CoA server (i.e., NAS) can decide which attributes are mandatory and which are not.


Instead, in the case of a CoA proxy, we say that all attributes MUST NOT be treated as mandatory. Proxies implementing this specification MUST perform proxying based on Operator-Name. Other schemes are possible but are not discussed here. Proxies SHOULD forward all packets either "as is" or with minimal changes.


We note that some NAS implementations currently treat signaling attributes as mandatory. For example, some NAS implementations will NAK any CoA packet that contains a Proxy-State attribute. While this behavior is based on a straightforward reading of the above text, it causes problems in practice.


We update Section 2.3 of [RFC5176] as follows: in CoA-Request and Disconnect-Request packets, the NAS MUST NOT treat as mandatory any attribute that is known to not affect the user's session -- for example, the Proxy-State attribute. Proxy-State is an attribute used for proxy-to-proxy signaling. It cannot affect the user's session, and therefore Proxy-State (and similar attributes) MUST be ignored by the NAS.


When Operator-Name and/or Operator-NAS-Identifier are received by a proxy, the proxy MUST pass those attributes through unchanged. This requirement applies to all proxies, including proxies that forward any or all of Access-Request, Accounting-Request, CoA-Request, and Disconnect-Request packets.


All attributes added by a RADIUS proxy when sending packets from the visited network to the home network MUST be removed by the corresponding CoA proxy from packets traversing the reverse path. That is, any editing of attributes that is done on the "forward" path MUST be undone on the "reverse" path.


The result is that a NAS will only ever receive CoA packets that either contain (1) attributes sent by the NAS to its local RADIUS server or (2) attributes that are sent by the home server in order to perform a change of authorization.


Finally, we extend the above requirement not only to Operator-Name and Operator-NAS-Identifier but also to any future attributes that are added for proxy-to-proxy signaling.


5. Functionality
5. 功能

This section describes how the two attributes work together to permit CoA proxying.


5.1. User Login
5.1. 用户登录

In this scenario, we follow a roaming user who is attempting to log in to a visited network. The login attempt is done via a NAS in the visited network. That NAS will send an Access-Request packet to the visited RADIUS server. The visited RADIUS server will see that the user is roaming and will add an Operator-Name attribute, with value "1" followed by its own realm name, e.g., "". The visited RADIUS server MAY also add an Operator-NAS-Identifier attribute. The NAS identification attributes are also edited, as required by Section 3.4, above.


The visited server will then proxy the authentication request to an upstream server. That server may be the home server, or it may be a proxy. In the case of a proxy, the proxy will forward the packet until the packet reaches the home server.


The home server will record the Operator-Name and Operator-NAS-Identifier attributes, along with other information about the user's session, if those attributes are present in a packet.


5.2. CoA Proxying
5.2. CoA代理

At some later point in time, the home server determines that (1) a user session should have its authorization changed or (2) the user should be disconnected. The home server looks up the Operator-Name and Operator-NAS-Identifier attributes, along with other user session identifiers as described in [RFC5176]. The home server then looks up the realm from the Operator-Name attribute in the logical AAA routing table, in order to find the next-hop CoA server for that realm (which may be a proxy). The CoA-Request is then sent to that CoA server.

在稍后的某个时间点,家庭服务器确定(1)用户会话应更改其授权或(2)用户应断开连接。家庭服务器查找操作员名称和操作员NAS标识符属性,以及[RFC5176]中所述的其他用户会话标识符。然后,家庭服务器从逻辑AAA路由表中的Operator Name属性中查找域,以便找到该域的下一个跃点CoA服务器(可能是代理)。然后将CoA请求发送到该CoA服务器。

The CoA server receives the request and, if it is a proxy, performs a lookup similar to the lookup done by the home server. The packet is then proxied repeatedly until it reaches the visited network.


If the proxy cannot find a destination for the request or if no Operator-Name attribute exists in the request, the proxy will return a CoA-NAK with Error-Cause 502 ("Request Not Routable").

如果代理找不到请求的目的地,或者请求中不存在操作员名称属性,则代理将返回一个CoA NAK,错误原因为502(“请求不可路由”)。

The visited network will receive the CoA-Request packet and will use the Operator-NAS-Identifier attribute (if available) to determine which local CoA server (i.e., NAS) the packet should be sent to. If there is no Operator-NAS-Identifier attribute, the visited network may use other means to locate the NAS, such as consulting a local database that tracks user sessions.


The Operator-Name and Operator-NAS-Identifier attributes are then removed from the packet; one of NAS-IP-Address, NAS-IPv6-Address, or NAS-Identifier is added to the packet; and the packet is then sent to the CoA server.

然后从数据包中删除操作员名称和操作员NAS标识符属性;向数据包添加NAS IP地址、NAS-IPv6-Address或NAS标识符中的一个;然后,数据包被发送到CoA服务器。

If no CoA server can be found, the visited network returns a CoA-NAK with Error-Cause 403 ("NAS Identification Mismatch").

如果找不到CoA服务器,访问的网络返回一个CoA NAK,错误原因为403(“NAS标识不匹配”)。

Any response from the CoA server (NAS) is returned to the home network via the normal method of returning responses to requests.


6. Security Considerations
6. 安全考虑

This specification incorporates by reference Section 11 of [RFC6929]. In short, RADIUS has many known issues; those issues are discussed in detail in [RFC6929] and do not need to be repeated here.


This specification adds one new attribute and defines new behavior for RADIUS proxying. As this behavior mirrors existing RADIUS proxying, we do not believe that it introduces any new security issues. We note, however, that RADIUS proxying has many inherent security issues.


6.1. RADIUS Security and Proxies
6.1. RADIUS安全和代理

The requirement that packets be signed with a shared secret means that a CoA packet can only be received from a trusted party or, transitively, received from a third party via a trusted party. This security provision of the base RADIUS protocol makes it impossible for untrusted parties to affect the user's session.


When RADIUS proxying is performed, all packets are signed on a hop-by-hop basis. Any intermediate proxy can therefore forge packets, replay packets, or modify the contents of any packet. Any system receiving correctly signed packets must accept them at face value and is unable to detect any forgery, replay, or modifications. As a result, the secure operation of such a system depends largely on trust instead of on technical means.


CoA packet proxying has all of the same issues as those noted above. We note that the proxies that see and can modify CoA packets are generally the same proxies that can see or modify Access-Request and Accounting-Request packets. As such, there are few additional security implications in allowing CoA proxying.


The main security implication that remains is that home networks now have the ability to disconnect or change the authorization of users in a visited network. As this capability is only enabled when mutual agreement is in place, and only for those parties who can already control user sessions, there are no new security issues with this specification.


6.2. Security of the Operator-NAS-Identifier Attribute
6.2. 操作员NAS标识符属性的安全性

Nothing in this specification depends on the security of the Operator-NAS-Identifier attribute. The entire process would work exactly the same if the Operator-NAS-Identifier attribute simply contained the NAS IP address that is hosting the user's session. The only real downside in that situation would be that external parties would see some additional private information about the visited network. They would still, however, be unable to leverage that information to do anything malicious.

本规范中的任何内容都不取决于操作员NAS标识符属性的安全性。如果Operator NAS Identifier属性仅包含承载用户会话的NAS IP地址,则整个过程将完全相同。在这种情况下,唯一真正的缺点是外部各方会看到有关访问网络的一些额外的私人信息。然而,他们仍然无法利用这些信息做任何恶意的事情。

The main reason to use an opaque token for the Operator-NAS-Identifier attribute is that there is no compelling reason to make the information public. We therefore recommend that the value be simply an opaque token. We also state that there is no requirement for integrity protection or replay detection of this attribute. The rest of the RADIUS protocol ensures that modification or replay of the Operator-NAS-Identifier attribute will either have no effect or have the same effect as if the value had not been modified.


Trusted parties can modify a user's session on the NAS only when they have sufficient information to identify that session. In practice, this limitation means that those parties already have access to the user's session information. In other words, those parties are the proxies who are already forwarding Access-Request and Accounting-Request packets.


Since those parties already have the ability to see and modify all of the information about a user's session, there is no additional security issue with allowing them to see and modify CoA packets.


In short, any security issues with the contents of Operator-NAS-Identifier are largely limited by the security of the underlying RADIUS protocol. This limitation means that it does not matter how the values of Operator-NAS-Identifier are created, stored, or used.


7. IANA Considerations
7. IANA考虑

Per Section 3.4 of this document, IANA has allocated one new RADIUS attribute (the Operator-NAS-Identifier attribute) from the "short extended space" of the "RADIUS Attribute Types" registry as follows:


Value: 241.8 Description: Operator-NAS-Identifier Data Type: string Reference: RFC 8559

值:241.8说明:操作员NAS标识符数据类型:字符串参考:RFC 8559

8. References
8. 工具书类
8.1. Normative References
8.1. 规范性引用文件

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <>.

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,DOI 10.17487/RFC2119,1997年3月<>.

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, DOI 10.17487/RFC2865, June 2000, <>.

[RFC2865]Rigney,C.,Willens,S.,Rubens,A.,和W.Simpson,“远程认证拨入用户服务(RADIUS)”,RFC 2865,DOI 10.17487/RFC2865,2000年6月<>.

[RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication Dial In User Service (RADIUS) Implementation Issues and Suggested Fixes", RFC 5080, DOI 10.17487/RFC5080, December 2007, <>.

[RFC5080]Nelson,D.和A.DeKok,“通用远程身份验证拨入用户服务(RADIUS)实施问题和建议修复”,RFC 5080,DOI 10.17487/RFC5080,2007年12月<>.

[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 5176, DOI 10.17487/RFC5176, January 2008, <>.

[RFC5176]Chiba,M.,Dommety,G.,Eklund,M.,Mitton,D.,和B.Aboba,“远程认证拨号用户服务(RADIUS)的动态授权扩展”,RFC 5176,DOI 10.17487/RFC5176,2008年1月<>.

[RFC5580] Tschofenig, H., Ed., Adrangi, F., Jones, M., Lior, A., and B. Aboba, "Carrying Location Objects in RADIUS and Diameter", RFC 5580, DOI 10.17487/RFC5580, August 2009, <>.

[RFC5580]Tschofenig,H.,Ed.,Adrangi,F.,Jones,M.,Lior,A.,和B.Aboba,“以半径和直径携带定位物体”,RFC 5580,DOI 10.17487/RFC5580,2009年8月<>.

[RFC6929] DeKok, A. and A. Lior, "Remote Authentication Dial In User Service (RADIUS) Protocol Extensions", RFC 6929, DOI 10.17487/RFC6929, April 2013, <>.

[RFC6929]DeKok,A.和A.Lior,“远程身份验证拨入用户服务(RADIUS)协议扩展”,RFC 6929,DOI 10.17487/RFC6929,2013年4月<>.

[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, DOI 10.17487/RFC7542, May 2015, <>.

[RFC7542]DeKok,A.,“网络访问标识符”,RFC 7542,DOI 10.17487/RFC7542,2015年5月<>.

[RFC8044] DeKok, A., "Data Types in RADIUS", RFC 8044, DOI 10.17487/RFC8044, January 2017, <>.

[RFC8044]DeKok,A.,“半径中的数据类型”,RFC 8044,DOI 10.17487/RFC8044,2017年1月<>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <>.

[RFC8174]Leiba,B.,“RFC 2119关键词中大写与小写的歧义”,BCP 14,RFC 8174,DOI 10.17487/RFC8174,2017年5月<>.

8.2. Informative References
8.2. 资料性引用

[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, DOI 10.17487/RFC2866, June 2000, <>.

[RFC2866]Rigney,C.,“半径会计”,RFC 2866,DOI 10.17487/RFC2866,2000年6月<>.

Authors' Addresses


Alan DeKok The FreeRADIUS Server Project

Alan DeKok FreeRADIUS服务器项目


Jouni Korhonen