Network Working Group David Nelson INTERNET-DRAFT Enterasys Networks Updates: 2865, 2866, 2869, 3576, 3579 Alan DeKok Category: Proposed Standard FreeRADIUS <draft-ietf-radext-fixes-00.txt> 19 December 2006 Common RADIUS Implementation Issues and Suggested Fixes By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 19, 2007. Copyright Notice Copyright (C) The IETF Trust (2006). All rights reserved. Abstract This document describes common issues seen in RADIUS implementations and suggests some fixes. Where applicable, ambiguities and errors in previous RADIUS specifications are clarified. Nelson, et al. Proposed Standard [Page 1]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 Table of Contents 1. Introduction .......................................... 3 1.1 Terminology ..................................... 3 1.2 Requirements Language ........................... 3 2. Issues ................................................ 4 2.1 Session Definition .............................. 4 2.2 Overload Conditions ............................. 6 2.3 Accounting Issues ............................... 7 2.4 Multiple Filter-ID Attributes ................... 9 2.5 Mandatory and Optional Attributes ............... 9 2.6 Interpretation of Access-Reject ................. 10 2.7 Addressing ...................................... 12 2.8 Idle Timeout .................................... 13 2.9 Unknown Identity ................................ 14 2.10 Responses after retransmissions ................. 15 2.11 Framed-IPv6-Prefix .............................. 15 3. IANA Considerations ................................... 16 4. Security Considerations ............................... 16 5. References ............................................ 17 5.1 Informative References ................................ 17 ACKNOWLEDGMENTS .............................................. 18 AUTHORS' ADDRESSES ........................................... 18 Intellectual Property Statement .............................. 19 Disclaimer of Validity ....................................... 22 Copyright Statement .......................................... 22 Nelson, et al. Proposed Standard [Page 2]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 1. Introduction The last few years have seen an increase in the deployment of RADIUS clients and servers. This document describes common issues seen in RADIUS implementations and suggests some fixes. Where applicable, ambiguities and errors in previous RADIUS specifications are clarified. 1.1. Terminology This document uses the following terms: Network Access Server (NAS) The device providing access to the network. Also known as the Authenticator (IEEE 802.1X or EAP terminology) or RADIUS client. service The NAS provides a service to the user, such as network access via 802.11 or PPP. session Each service provided by the NAS to a peer constitutes a session, with the beginning of the session defined as the point where service is first provided and the end of the session defined as the point where service is ended. A peer may have multiple sessions in parallel or series if the NAS supports that, with each session generating a separate start and stop accounting record. silently discard This means the implementation discards the packet without further processing. The implementation SHOULD provide the capability of logging the error, including the contents of the silently discarded packet, and SHOULD record the event in a statistics counter. 1.2. Requirements Language In this document, several words are used to signify the requirements of the specification. 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]. Nelson, et al. Proposed Standard [Page 3]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 2. Issues 2.1. Session Definition 2.1.1. State Attribute Regarding the State attribute, [RFC2865] Section 5.24 states: This Attribute is available to be sent by the server to the client in an Access-Challenge and MUST be sent unmodified from the client to the server in the new Access-Request reply to that challenge, if any. This Attribute is available to be sent by the server to the client in an Access-Accept that also includes a Termination-Action Attribute with the value of RADIUS-Request. If the NAS performs the Termination-Action by sending a new Access-Request upon termination of the current session, it MUST include the State attribute unchanged in that Access-Request. Some RADIUS client implementations do not properly use the State attribute in order to distinguish a restarted EAP authentication process from the continuation of an ongoing process (by the same user on the same NAS and port). Where an EAP-Message attribute is included in an Access-Challenge or Access-Accept attribute, RADIUS servers SHOULD also include a State attribute. An Access-Request sent as a result of a new or restarted authentication run MUST NOT include the State attribute, even if the State attribute has previously been received in an Access-Challenge for the same user and port. Since a State attribute is always initially provided by the server in an Access-Accept, Access-Challenge, CoA-Request or Disconnect- Request, a RADIUS client MUST NOT insert a State attribute that it has not previously received from the server. A State attribute is REQUIRED in Access-Request packets neither including an authentication attribute nor a Service-Type attribute with the value Call Check (10). 2.1.2. Request-ID Supplementation [RFC3579] Section 2.6.1 states: In EAP, each session has its own unique Identifier space. RADIUS Nelson, et al. Proposed Standard [Page 4]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 server implementations MUST be able to distinguish between EAP packets with the same Identifier existing within distinct sessions, originating on the same NAS. For this purpose, sessions can be distinguished based on NAS and session identification attributes. NAS identification attributes include NAS-Identifier, NAS-IPv6-Address and NAS-IPv4-Address. Session identification attributes include User-Name, NAS-Port, NAS-Port-Type, NAS-Port- Id, Called-Station-Id, Calling-Station-Id and Originating-Line- Info. There are issues with the suggested algorithm. Since proxies may modify Access-Request attributes such as NAS-IP-Address, depending on any attribute under control of the NAS to distinguish request identifiers can result in deployment problems. The FreeRADIUS implementation does not track EAP identifiers by NAS- IP-Address or other non-EAP attributes sent by the NAS. Instead, it uses the EAP identifier, source IP address, and the State attribute as a "key" to uniquely identify each EAP session. Since the State attribute is under the control of the RADIUS server, this means that the uniqueness of each session is controlled by the server, not the NAS. The algorithm used in FreeRADIUS is as follows: if (EAP start, or EAP identity) { allocate unique State Attribute insert session into "active session" table with key (EAP identifier, State, source IP) } else { look up active session in table, with above key } This algorithm appears to work well in variety of situations, including situations where home servers receive messages via intermediate RADIUS proxies. 2.2. Overload Conditions 2.2.1. Retransmission Behavior [RFC2865] Section 2.4 describes the retransmission requirements for RADIUS clients: At one extreme, RADIUS does not require a "responsive" detection of lost data. The user is willing to wait several seconds for the authentication to complete. The generally aggressive TCP retransmission (based on average round trip time) is not required, nor is the acknowledgment overhead of TCP. Nelson, et al. Proposed Standard [Page 5]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 At the other extreme, the user is not willing to wait several minutes for authentication. Therefore the reliable delivery of TCP data two minutes later is not useful. The faster use of an alternate server allows the user to gain access before giving up. Some existing RADIUS clients implement excessively aggressive retransmission behavior, utilizing default retransmission timeouts of one second or less without support for congestive backoff. When deployed at large scale, these implementations are susceptible to congestive collapse. For example, as the result of a power failure, a network with 3000 NAS devices with a fixed retransmission timer of one second will continuously generate 3000 RADIUS Access-Requests per second. This is sufficient to overwhelm most RADIUS servers. Suggested solutions include: [a] Jitter. To avoid synchronization, a RADIUS client SHOULD incorporate jitter within its retransmission algorithm. [b] Congestive backoff. While it is not necessary for RADIUS client implementations to implement complex retransmission algorithms, implementations SHOULD support congestive backoff within the limits suggested by [RFC2865] Section 2.4. For example, an implementation SHOULD double the initial retransmission timer until a maximum retransmission time is reached, after which the client will failover to another RADIUS server. For example, if the initial retransmission timer is one second, a maximum retransmission timer of 16 seconds might be used. 2.2.2. Server Response to Overload Some RADIUS server implementations are not robust in response to overload, dropping packets with even probability across multiple sessions. In an overload situation, this results in a high failure rate for multi-round authentication protocols such as EAP [RFC3579]. Typically, users will continually retry in an attempt to gain access, increasing the load even further. A more sensible approach is for a RADIUS server to preferentially accept RADIUS Access-Request packets containing a valid State attribute, so that multi-round authentication conversations, once begun, will be more likely to succeed. Similarly, a server that is proxying requests should preferentially process Access-Accept, Access-Challenge, or Access-Reject packets from home servers, before processing new requests from a NAS. These methods will allow some users to gain access to the network, reducing the load created by ongoing access attempts. Nelson, et al. Proposed Standard [Page 6]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 2.3. Accounting Issues 2.3.1. Attributes allowed in an Interim Update [RFC2866] indicates that Acct-Input-Octets, Acct-Output-Octets, Acct- Session-Time, Acct-Input-Packets, Acct-Output-Packets and Acct- Terminate-Cause attributes "can only be present in Accounting-Request records where the Acct-Status-Type is set to Stop." However [RFC2869] Section 2.1 states: It is envisioned that an Interim Accounting record (with Acct- Status-Type = Interim-Update (3)) would contain all of the attributes normally found in an Accounting Stop message with the exception of the Acct-Term-Cause attribute. Although [RFC2869] does not indicate that it updates [RFC2866], this is an oversight, and the above attributes are allowable in an Interim Accounting record. 2.3.2. NAS handling of Acct-Interim-Update [RFC2869] Section 2.1 states It is also possible to statically configure an interim value on the NAS itself. Note that a locally configured value on the NAS MUST override the value found in an Access-Accept. This requirement may be too strong in practice. If an implementator chooses to permit the Acct-Interim-Interval in an Access-Accept to override a global default for that value, then the implementation MUST enforce a minimum acceptable value on the Acct-Interim-Interval in an Access-Accept. The alternative would be to accept inappropriately small values, which may have performance impact on the NAS. This minimum SHOULD be configurable on the NAS, as a "minimim acceptable Acct-Intim-Interval". 2.3.3. Acct-Session-Id and Acct-Multi-Session-Id [RFC2866] Section 5.5 describes Acct-Session-Id as Text within the description, but also states that "The String field SHOULD be a string of UTF-8 encoded 10646 characters." Since Acct-Multi-Session-Id is consistently described as a String, it appears that this is a typographical error, and that Acct-Session-Id is of type String. Nelson, et al. Proposed Standard [Page 7]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 The implication is that a robust implementation SHOULD support the String fields within Acct-Session-Id and Acct-Multi-Session-Id as undistinguished octets. 2.3.4. Request Authenticator [RFC2866] Section 4.1 states: The Request Authenticator of an Accounting-Request contains a 16-octet MD5 hash value calculated according to the method described in "Request Authenticator" above. However, the text does not indicate any action to take when an Accounting-Request packet contains an invalid Request Authenticator. The following text should be considered to be part of the above description: The Request Authenticator field MUST contain the correct data, as given by the above calculation. Invalid packets are silently discarded. Note that some early implementations always set the Request Authenticator to all zeros. New implementations of RADIUS clients MUST use the above algorithm to calculate the Request Authenticator field. New RADIUS server implementations MUST silently discard invalid packets. 2.4. Multiple Filter-ID Attributes [RFC2865] Section 5.11 states: Zero or more Filter-Id attributes MAY be sent in an Access-Accept packet. In practice the behavior of a RADIUS client receiving multiple Filter-ID attributes is implementation dependent. For example, some implementations treat multiple instances of the Filter-ID attribute as alternative filters; the first Filter-ID attribute having a name matching a locally defined filter is used, and the remaining ones are discarded. Other implementations may combine matching filters. As a result, the interpretation of multiple Filter-ID attributes is undefined within RADIUS. The sending of multiple Filter-ID attributes within an Access-Accept SHOULD be avoided within heterogeneous deployments and roaming scenarios, where it is likely to produce unpredictable results. Nelson, et al. Proposed Standard [Page 8]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 2.5. Mandatory and Optional Attributes RADIUS attributes do not explicitly state whether they are optional or mandatory. Nevertheless there are instances where RADIUS attributes need to be treated as mandatory. [RFC2865] Section 1.1 states: A NAS that does not implement a given service MUST NOT implement the RADIUS attributes for that service. For example, a NAS that is unable to offer ARAP service MUST NOT implement the RADIUS attributes for ARAP. A NAS MUST treat a RADIUS access-accept authorizing an unavailable service as an access-reject instead. With respect to the Service-Type attribute, [RFC2865] Section 5.6 says: This Attribute indicates the type of service the user has requested, or the type of service to be provided. It MAY be used in both Access-Request and Access-Accept packets. A NAS is not required to implement all of these service types, and MUST treat unknown or unsupported Service-Types as though an Access-Reject had been received instead. [RFC2865] Section 5 states: A RADIUS server MAY ignore Attributes with an unknown Type. A RADIUS client MAY ignore Attributes with an unknown Type. With respect to Vendor-Specific Attributes (VSAs), [RFC2865] Section 5.26 states: Servers not equipped to interpret the vendor-specific information sent by a client MUST ignore it (although it may be reported). Clients which do not receive desired vendor-specific information SHOULD make an attempt to operate without it, although they may do so (and report they are doing so) in a degraded mode. It is possible for either a standard attribute or VSA to represent a request for an unavailable service. However, where the Type or Vendor-ID is unknown, a RADIUS client will not know whether the attribute defines a service or not. In general, it is best for RADIUS clients to err on the side of caution. On receiving an Access-Accept including an attribute of unknown Type, a RADIUS client SHOULD assume that it is a potential service definition, and treat it as an Access-Reject. Unknown VSAs SHOULD be ignored by RADIUS clients. Nelson, et al. Proposed Standard [Page 9]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 RADIUS authentication server implementations SHOULD ignore attributes of unknown Type. Since RADIUS accounting server implementations typically do not need to understand attributes in order to write them to stable storage or pass them to the billing engine, accounting server implementations SHOULD be equipped to handle unknown attributes. To avoid misinterpretation of service requests encoded within VSAs, RADIUS servers SHOULD NOT send VSAs containing service requests to RADIUS clients that are not known to understand them. For example, a RADIUS server should not send a VSA encoding a filter without knowledge that the RADIUS client supports the VSA. 2.6. Interpretation of Access-Reject 2.6.1. Improper Use of Access-Reject The intent of an Access-Reject is to deny access to the requested service. [RFC2865] Section 2 states: If any condition is not met, the RADIUS server sends an "Access- Reject" response indicating that this user request is invalid. If desired, the server MAY include a text message in the Access- Reject which MAY be displayed by the client to the user. No other Attributes (except Proxy-State) are permitted in an Access-Reject. This text makes it clear that RADIUS does not allow the provisioning of services within an Access-Reject. If the desire is to allow limited access, then an Access-Accept can be sent with attributes provisioning limited access. Attributes within an Access-Reject are restricted to those necessary to route the message (e.g. Proxy- State), attributes providing the user with an indication that access has been denied (e.g. an EAP-Message attribute containing an EAP- Failure) or attributes conveying an error message (e.g. a Reply- Message or Error-Cause attribute). Unfortunately, there are examples where this requirement has been misunderstood. [RFC2869] Section 2.2 states: If that authentication fails, the RADIUS server should return an Access-Reject packet to the NAS, with optional Password-Retry and Reply-Messages attributes. The presence of Password-Retry indicates the ARAP NAS MAY choose to initiate another challenge- response cycle, This paragraph is problematic from two perspectives. Firstly, a Password-Retry attribute is being returned in an Access-Reject; this attribute does not fit into the categories established in [RFC2865]. Nelson, et al. Proposed Standard [Page 10]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 Secondly, an Access-Reject packet is being sent in the context of a continuing authentication conversation; [RFC2865] requires use of an Access-Challenge for this. [RFC2869] uses the phrase "challenge- response" to describe this use of Access-Reject, indicating that the semantics of Access-Challenge are being used. [RFC2865] Section 4.4, addresses the semantics of Access-Challenge being equivalent to Access-Reject in some cases: If the NAS does not support challenge/response, it MUST treat an Access-Challenge as though it had received an Access-Reject instead. While it is difficult to correct existing deployments of [RFC2869], we make the following recommendations: [1] New RADIUS specifications and implementations MUST NOT use Access- Reject where the semantics of Access-Challenge are intended. [2] Access-Reject MUST mean denial of access to the requested service. In response to an Access-Reject, the NAS MUST NOT send any additional Access-Request packets for that user session. [3] New deployments of ARAP [RFC2869] SHOULD use Access-Challenge instead of Access-Reject packets in the conversations described in [RFC2869] Section 2.2. We also note that the table of attributes [RFC2869] Section 5.19 has an error for the Password-Retry attribute. It says: Request Accept Reject Challenge # Attribute 0 0 0-1 0 75 Password-Retry However, the text in [RFC2869] Section 2.3.2 says that Password-Retry can be included within an Access-Challenge packet, for EAP authentication sessions. We recommend a correction to the table: Request Accept Reject Challenge # Attribute 0 0 0 0-1 75 Password-Retry [Note 2] [Note 2] As per RFC 3579, the use of the Password-Retry in EAP authentications is deprecated. The Password-Retry attribute can be used only for ARAP authentication. 2.6.2. Service Request Denial RADIUS has been deployed for purposes outside network access authentication, authorization and accounting. For example, RADIUS Nelson, et al. Proposed Standard [Page 11]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 has been deployed as a "back-end" for authenticating VOIP connections, HTTP sessions (e.g. Apache), FTP sessions (e.g. proftpd), and machine logins for multiple operating systems (e.g. bsdi, pam, gina). In those contexts, an Access-Reject sent to the RADIUS client MUST be interpreted as a rejection of the request for service, and the RADIUS client MUST NOT offer that service to the user. For example, when an authentication failure occurs in the context of an FTP session, the normal semantics for rejecting FTP services apply. The rejection does not necessarily cause the FTP server to terminate the underlying TCP connection, but the FTP server MUST NOT offer any services protected by user authentication. Users may request multiple services from the NAS. Where those services are independent, the deployment MUST treat the RADIUS sessions as being independent. For example, a NAS may offer multi-link services, where a user may have multiple simultaneous network connections. In that case, an Access-Reject for a later multi-link connection request does not necessarily mean that earlier multi-link connections are torn down. Similarly, if a NAS offers both dialup and VOIP services, the rejection of a VOIP attempt does not mean that the dialup session is torn down. Where a NAS offers multiple services, confusion may result with respect to interpretation of a Disconnect-Request [RFC3576]. In order to prevent confusion a RADIUS Server SHOULD identify the session that it desires to terminate as specifically as possible. For example, an Acct-Session-Id attribute SHOULD be included in Disconnect-Request and CoA-Request packets, rather than just the User-Name attribute. 2.7. Addressing 2.7.1. Link-Local Addresses Since Link-Local addresses are unique only on the local link, if the NAS and RADIUS server are not on the same link, then an IPv6 Link- Local address [RFC2462] or an IPv4 Link-Local Address [RFC3927] cannot be used to uniquely identify the NAS. A RADIUS server receiving a NAS-IPv6-Address or NAS-IP-Address attribute containing a Link-Local address SHOULD NOT count such an attribute toward satisfying the requirements of [RFC3162] Section 2.1: NAS-IPv6-Address and/or NAS-IP-Address MAY be present in an Access-Request packet; however, if neither attribute is present Nelson, et al. Proposed Standard [Page 12]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 then NAS-Identifier MUST be present. 2.7.2. Multiple Addresses There are situations in which a RADIUS client or server may have multiple addresses. For example, a dual stack host can have both IPv4 and IPv6 addresses; a host that is a member of multiple VLANs could have IPv4 and/or IPv6 addresses on each VLAN; a host can have multiple IPv4 or IPv6 addresses on a single interface. However, [RFC2865] Section 5.44 only permits zero or one NAS-IP-Address attribute within an Access-Request and [RFC3162] Section 3 only permits zero or one NAS-IPv6-Address attribute within an Access- Request. When a NAS has more than one global address and no ability to determine which is used for identification in a particular request, it is RECOMMENDED that the NAS include the NAS-Identifier attribute in an Access-Request in order to identify itself to the RADIUS server. [RFC2865] Section 3 states: A RADIUS server MUST use the source IP address of the RADIUS UDP packet to decide which shared secret to use, so that RADIUS requests can be proxied. Therefore if a RADIUS client sends packets from more than one source address, a shared secret will need to be configured on both the client and server for each source address. 2.8. Idle-Timeout With respect to the Idle-Timeout attribute, [RFC2865] Section 5.28 states: This Attribute sets the maximum number of consecutive seconds of idle connection allowed to the user before termination of the session or prompt. This Attribute is available to be sent by the server to the client in an Access-Accept or Access-Challenge. [RFC3580] Section 3.12 states: The Idle-Timeout attribute is described in [RFC2865]. For IEEE 802 media other than 802.11 the media are always on. As a result the Idle-Timeout attribute is typically only used with wireless media such as IEEE 802.11. It is possible for a wireless device to wander out of range of all Access Points. In this case, the Idle-Timeout attribute indicates the maximum time that a wireless device may remain idle. Nelson, et al. Proposed Standard [Page 13]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 In the above paragraphs "idle" may not necessarily mean "no traffic"; the NAS may support filters defining what traffic is included in the idle time determination. As a result, an "idle connection" is defined by local policy in the absence of other attributes. 2.9. Unknown Identity [RFC3748] Section 5.1 states: If the Identity is unknown, the Identity Response field should be zero bytes in length. However, [RFC2865] Section 5.1 describes the User-Name attribute as follows: The String field is one or more octets. How should the RADIUS client behave if it receives an EAP- Response/Identity that is zero octets in length? [RFC2865] Section 5.1 states: This Attribute indicates the name of the user to be authenticated. It MUST be sent in Access-Request packets if available. This suggests that the User-Name attribute may be ommitted if it is unavailable. However, [RFC3579] Section 2.1 states: In order to permit non-EAP aware RADIUS proxies to forward the Access-Request packet, if the NAS initially sends an EAP-Request/Identity message to the peer, the NAS MUST copy the contents of the Type-Data field of the EAP-Response/Identity received from the peer into the User-Name attribute and MUST include the Type-Data field of the EAP-Response/Identity in the User-Name attribute in every subsequent Access-Request. This suggests that the User-Name attribute should contain the contents of the Type-Data field of the EAP-Response/Identity, even if it is zero octets in length. Note that [RFC4282] does not permit an NAI of zero octets, so that an EAP-Response/Identity with a Type-Data field of zero octets MUST NOT be construed as a request for privacy (e.g. anonymous NAI). When a NAS receives an EAP-Response/Identity with a Type-Data field that is zero octets in length, it is RECOMMENDED that it either omit Nelson, et al. Proposed Standard [Page 14]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 a User-Name attribute in the Access-Request or include the Calling- Station-Id in the User-Name attribute, along with a Calling-Station- Id attribute. 2.10. Responses after retransmissions. Some implementations do not correctly handle the receipt of RADIUS responses after retransmissions. [RFC2865] Section 2.5 states If the NAS is retransmitting a RADIUS request to the same server as before, and the attributes haven't changed, you MUST use the same Request Authenticator, ID, and source port. If any attributes have changed, you MUST use a new Request Authenticator and ID. Note that changing the Request ID for a retransmission may have undesirable side effects. Since RADIUS does not have a clear definition of a "session", it is perfectly valid for a RADIUS server to treat a retransmission as a new session request, and to reject it due to (say) multiple simultaneous login restrictions are enforced. In that situation, the NAS may receive a belated Access-Accept for the first request, and an Access-Reject for the retransmitted request, both of which apply to the same "session". We suggest that the contents of Access-Request packets SHOULD NOT be changed during retransmissions. If they must be changed due to the inclusion of an Event-Timestampt attribute, for example, then responses to earlier transmissions MUST be silently discarded. Any response to the current request MUST be treated as the definitive response, even if as noted above, it disagrees with earlier responses. This problem can be made worse by implementations that use a fixed retransmission timeout (30 seconds is common). We reiterate the suggestions above in Section 2.1 about using congestive backoff. In that case, responses to earlier transmissions MAY be used as data points for congestive backoff, even if their contents are discarded. 2.11. Framed-IPv6-Prefix [RFC3162] Section 2.3 says This Attribute indicates an IPv6 prefix (and corresponding route) to be configured for the user. It MAY be used in Access-Accept packets, and can appear multiple times. It MAY be used in an Access-Request packet as a hint by the NAS to the server that it would prefer these prefix(es), but the server is not required to honor the hint. Since it is assumed that the NAS will plumb a Nelson, et al. Proposed Standard [Page 15]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 route corresponding to the prefix, it is not necessary for the server to also send a Framed-IPv6-Route attribute for the same prefix. If an ISP desires to support Prefix Delegation at the same time that it would like to assign a prefix for the link between the NAS and customer premises equipment (CPE). In this situation, the sematics of Framed-IPv6-Prefix may be unclear, in that it is difficult to know which prefixes are to be used for delegation, and which one is to be used for the link. The intent of the paragraph was to enable the NAS to advertise the prefix (such as via a Router Advertisement). If the Framed-Routing attribute is used, it is also possible that the prefix would be advertised in a routing protocol such as RIPNG. RFC 2865 Section 5.10 describes the purpose of Framed-Routing: This Attribute indicates the routing method for the user, when the user is a router to a network. It is only used in Access-Accept packets. The description of the Prefix-Length field in RFC 3162 indicates excessively wide latitude: The length of the prefix, in bits. At least 0 and no larger than 128. This length appears too broad, because it is not clear what a NAS should do with a prefix of greater granularity than /64. For example, the Framed-IPv6-Prefix may contain a /128. This does not imply that the NAS should assign an IPv6 address to the end user, because RFC 3162 already defines a Framed-IPv6-Identifier attribute to handle the Identifier portion. It appears that the Framed-IPv6-Prefix is used for the link between the NAS and CPE only if a /64 prefix is assigned. When a larger prefix is sent, the intent is to provide the entire prefix to the CPE, enabling the CPE to assign sub-prefixes if it wishes to do so. 3. IANA Considerations This specification does not create any new registries, nor does it require assignment of any protocol parameters. 4. Security Considerations Since this document describes the use of RADIUS for purposes of authentication, authorization, and accounting in WLANs, it is vulnerable to all of the threats that are present in other RADIUS applications. For a discussion of these threats, see [RFC2865], Nelson, et al. Proposed Standard [Page 16]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 [RFC2607], [RFC3162], [RFC3576], [RFC3579], and [RFC3580]. 5. References 5.1. Informative references [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March, 1997. [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy Implementation in Roaming", RFC 2607, June 1999. [RFC2865] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. [RFC2867] Zorn, G., Aboba, B. and D. Mitton, "RADIUS Accounting Modifications for Tunnel Protocol Support", RFC 2867, June 2000. [RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M. and I. Goyret, "RADIUS Attributes for Tunnel Protocol Support", RFC 2868, June 2000. [RFC2869] Rigney, C., Willats, W. and P. Calhoun, "RADIUS Extensions", RFC 2869, June 2000. [RFC2882] Mitton, D., "Network Access Servers Requirements: Extended RADIUS Practices", RFC 2882, July 2000. [RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162, August 2001. [RFC3575] Aboba, B., "IANA Considerations for RADIUS", RFC 3575, July 2003. [RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 3576, July 2003. [RFC3579] Aboba, B. and P. Calhoun, "RADIUS Support for Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. Nelson, et al. Proposed Standard [Page 17]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese, "IEEE 802.1X Remote Authentication Dial In User Service (RADIUS) Usage Guidelines", RFC 3580, September 2003. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC3927] Cheshire, S., Aboba, B. and E. Guttman, "Dynamic Configuration of IPv4 Link-Local Addresses", RFC 3927, May 2005. [RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network Access Identifier", RFC 4282, December 2005. Acknowledgments The authors would like to acknowledge Glen Zorn for contributions to this document. The alternate algorithm to [RFC3579] Section 2.6.1 that is described in section 2.1.2 of this document was designed by Raghu Dendukuri. Authors' Addresses David B. Nelson Enterasys Networks 50 Minuteman Road Andover, MA 01810 Email: dnelson@enterasys.com Alan DeKok The FreeRADIUS Server Project http://freeradius.org/ Email: aland@freeradius.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Nelson, et al. Proposed Standard [Page 18]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Nelson, et al. Proposed Standard [Page 19]
INTERNET-DRAFT RADIUS Issues & Fixes 19 December 2006 Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Open issues Open issues relating to this specification are tracked on the following web site: http://www.drizzle.com/~aboba/RADEXT/ Nelson, et al. Proposed Standard [Page 20]
