draft-ietf-radext-radius-fragmentation-12.txt   rfc7499.txt 
RADIUS EXTensions Working Group A. Perez-Mendez Internet Engineering Task Force (IETF) A. Perez-Mendez, Ed.
Internet-Draft R. Marin-Lopez Request for Comments: 7499 R. Marin-Lopez
Intended status: Experimental F. Pereniguez-Garcia Category: Experimental F. Pereniguez-Garcia
Expires: July 30, 2015 G. Lopez-Millan ISSN: 2070-1721 G. Lopez-Millan
University of Murcia University of Murcia
D. Lopez D. Lopez
Telefonica I+D Telefonica I+D
A. DeKok A. DeKok
Network RADIUS Network RADIUS
January 26, 2015 April 2015
Support of fragmentation of RADIUS packets Support of Fragmentation of RADIUS Packets
draft-ietf-radext-radius-fragmentation-12
Abstract Abstract
The Remote Authentication Dial-In User Service (RADIUS) protocol is The Remote Authentication Dial-In User Service (RADIUS) protocol is
limited to a total packet size of 4096 octets. Provisions exist for limited to a total packet size of 4096 bytes. Provisions exist for
fragmenting large amounts of authentication data across multiple fragmenting large amounts of authentication data across multiple
packets, via Access-Challenge. No similar provisions exist for packets, via Access-Challenge packets. No similar provisions exist
fragmenting large amounts of authorization data. This document for fragmenting large amounts of authorization data. This document
specifies how existing RADIUS mechanisms can be leveraged to provide specifies how existing RADIUS mechanisms can be leveraged to provide
that functionality. These mechanisms are largely compatible with that functionality. These mechanisms are largely compatible with
existing implementations, and are designed to be invisible to existing implementations, and they are designed to be invisible to
proxies, and "fail-safe" to legacy RADIUS Clients and Servers. proxies and "fail-safe" to legacy RADIUS Clients and Servers.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is not an Internet Standards Track specification; it is
Task Force (IETF). Note that other groups may also distribute published for examination, experimental implementation, and
working documents as Internet-Drafts. The list of current Internet- evaluation.
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document defines an Experimental Protocol for the Internet
and may be updated, replaced, or obsoleted by other documents at any community. This document is a product of the Internet Engineering
time. It is inappropriate to use Internet-Drafts as reference Task Force (IETF). It represents the consensus of the IETF
material or to cite them other than as "work in progress." community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.
This Internet-Draft will expire on July 30, 2015. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7499.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6 1.1. Requirements Language ......................................6
2. Status of this document . . . . . . . . . . . . . . . . . . . 6 2. Status of This Document .........................................6
3. Scope of this document . . . . . . . . . . . . . . . . . . . . 7 3. Scope of This Document ..........................................7
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Overview .......................................................10
5. Fragmentation of packets . . . . . . . . . . . . . . . . . . . 12 5. Fragmentation of Packets .......................................13
5.1. Pre-authorization . . . . . . . . . . . . . . . . . . . . 13 5.1. Pre-Authorization .........................................14
5.2. Post-authorization . . . . . . . . . . . . . . . . . . . . 17 5.2. Post-Authorization ........................................18
6. Chunk size . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6. Chunk Size .....................................................21
7. Allowed large packet size . . . . . . . . . . . . . . . . . . 21 7. Allowed Large Packet Size ......................................22
8. Handling special attributes . . . . . . . . . . . . . . . . . 22 8. Handling Special Attributes ....................................23
8.1. Proxy-State attribute . . . . . . . . . . . . . . . . . . 22 8.1. Proxy-State Attribute .....................................23
8.2. State attribute . . . . . . . . . . . . . . . . . . . . . 23 8.2. State Attribute ...........................................24
8.3. Service-Type attribute . . . . . . . . . . . . . . . . . . 24 8.3. Service-Type Attribute ....................................25
8.4. Rebuilding the original large packet . . . . . . . . . . . 24 8.4. Rebuilding the Original Large Packet ......................25
9. New flag T field for the Long Extended Type attribute 9. New T Flag for the Long Extended Type Attribute Definition .....26
definition . . . . . . . . . . . . . . . . . . . . . . . . . . 24 10. New Attribute Definition ......................................26
10. New attribute definition . . . . . . . . . . . . . . . . . . . 25 10.1. Frag-Status Attribute ....................................27
10.1. Frag-Status attribute . . . . . . . . . . . . . . . . . . 25 10.2. Proxy-State-Length Attribute .............................28
10.2. Proxy-State-Length attribute . . . . . . . . . . . . . . . 26 10.3. Table of Attributes ......................................29
10.3. Table of attributes . . . . . . . . . . . . . . . . . . . 27 11. Operation with Proxies ........................................29
11. Operation with proxies . . . . . . . . . . . . . . . . . . . . 27 11.1. Legacy Proxies ...........................................29
11.1. Legacy proxies . . . . . . . . . . . . . . . . . . . . . . 28 11.2. Updated Proxies ..........................................29
11.2. Updated proxies . . . . . . . . . . . . . . . . . . . . . 28 12. General Considerations ........................................31
12. General considerations . . . . . . . . . . . . . . . . . . . . 30 12.1. T Flag ...................................................31
12.1. Flag T . . . . . . . . . . . . . . . . . . . . . . . . . . 30 12.2. Violation of RFC 2865 ....................................32
12.2. Violation of RFC2865 . . . . . . . . . . . . . . . . . . . 31 12.3. Proxying Based on User-Name ..............................32
12.3. Proxying based on User-Name . . . . . . . . . . . . . . . 31 12.4. Transport Behavior .......................................33
12.4. Transport behaviour . . . . . . . . . . . . . . . . . . . 31 13. Security Considerations .......................................33
13. Security Considerations . . . . . . . . . . . . . . . . . . . 32 14. IANA Considerations ...........................................34
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 15. References ....................................................35
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 15.1. Normative References .....................................35
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 15.2. Informative References ...................................35
16.1. Normative References . . . . . . . . . . . . . . . . . . . 34 Acknowledgements ..................................................37
16.2. Informative References . . . . . . . . . . . . . . . . . . 34 Authors' Addresses ................................................37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction 1. Introduction
The RADIUS [RFC2865] protocol carries authentication, authorization, The RADIUS [RFC2865] protocol carries authentication, authorization,
and accounting information between a RADIUS Client and an RADIUS and accounting information between a RADIUS Client and a RADIUS
Server. Information is exchanged between them through RADIUS Server. Information is exchanged between them through RADIUS
packets. Each RADIUS packet is composed of a header, and zero or packets. Each RADIUS packet is composed of a header, and zero or
more attributes, up to a maximum packet size of 4096 octets. The more attributes, up to a maximum packet size of 4096 bytes. The
protocol is a request/response protocol, as described in the protocol is a request/response protocol, as described in the
operational model ([RFC6158], Section 3.1). operational model ([RFC6158], Section 3.1).
The intention of the above packet size limitation was to avoid as The intention of the above packet size limitation was to avoid UDP
much as possible UDP fragmentation. Back then, 4096 seemed large fragmentation as much as possible. Back then, a size of 4096 bytes
enough for any purpose. Now, new scenarios are emerging that require seemed large enough for any purpose. Now, new scenarios are emerging
the exchange of authorization information exceeding this 4096 limit. that require the exchange of authorization information exceeding this
For instance, the Application Bridging for Federated Access Beyond 4096-byte limit. For instance, the Application Bridging for
web (ABFAB) IETF WG defines the transport of Security Assertion Federated Access Beyond web (ABFAB) IETF working group defines the
Markup Language (SAML) sentences from the RADIUS server to the RADIUS transport of Security Assertion Markup Language (SAML) statements
client [I-D.ietf-abfab-aaa-saml]. This assertion is likely to be from the RADIUS Server to the RADIUS Client [SAML-RADIUS]. This
larger than 4096 octets. assertion is likely to be larger than 4096 bytes.
This means that peers desiring to send large amounts of data must This means that peers desiring to send large amounts of data must
fragment it across multiple packets. For example, RADIUS-EAP fragment it across multiple packets. For example, RADIUS-EAP
[RFC3579] defines how an Extensible Authentication Protocol (EAP) [RFC3579] defines how an Extensible Authentication Protocol (EAP)
exchange occurs across multiple Access-Request / Access-Challenge exchange occurs across multiple Access-Request / Access-Challenge
sequences. No such exchange is possible for accounting or sequences. No such exchange is possible for accounting or
authorization data. [RFC6158] Section 3.1 suggests that exchanging authorization data. [RFC6158], Section 3.1 suggests that exchanging
large amounts authorization data is unnecessary in RADIUS. Instead, large amounts of authorization data is unnecessary in RADIUS.
the data should be referenced by name. This requirement allows large Instead, the data should be referenced by name. This requirement
policies to be pre-provisioned, and then referenced in an Access- allows large policies to be pre-provisioned and then referenced in an
Accept. In some cases, however, the authorization data sent by the Access-Accept. In some cases, however, the authorization data sent
RADIUS Server is large and highly dynamic. In other cases, the by the RADIUS Server is large and highly dynamic. In other cases,
RADIUS Client needs to send large amounts of authorization data to the RADIUS Client needs to send large amounts of authorization data
the RADIUS Server. Both of these cases are un-met by the to the RADIUS Server. Neither of these cases is met by the
requirements in [RFC6158]. As noted in that document, the practical requirements in [RFC6158]. As noted in that document, the practical
limit on RADIUS packet sizes is governed by the Path MTU (PMTU), limit on RADIUS packet sizes is governed by the Path MTU (PMTU),
which may be significantly smaller than 4096 octets. The combination which may be significantly smaller than 4096 bytes. The combination
of the two limitations means that there is a pressing need for a of the two limitations means that there is a pressing need for a
method to send large amounts of authorization data between RADIUS method to send large amounts of authorization data between RADIUS
Client and Server, with no accompanying solution. Client and Server, with no accompanying solution.
[RFC6158] section 3.1 recommends three approaches for the [RFC6158], Section 3.1 recommends three approaches for the
transmission of large amount of data within RADIUS. However, they transmission of large amounts of data within RADIUS. However, they
are not applicable to the problem statement of this document for the are not applicable to the problem statement of this document for the
following reasons: following reasons:
o The first approach (utilization of a sequence of packets) does not o The first approach (utilization of a sequence of packets) does not
talk about large amounts of data sent from the RADIUS Client to a talk about large amounts of data sent from the RADIUS Client to a
RADIUS Server. Leveraging EAP (request/challenge) to send the RADIUS Server. Leveraging EAP (request/challenge) to send the
data is not feasible, as EAP already fills packet to PMTU, and not data is not feasible, as EAP already fills packets to PMTU, and
all authentications use EAP. Moreover, as noted for NAS-Filter- not all authentications use EAP. Moreover, as noted for the
Rule ([RFC4849]), this approach does not entirely solve the NAS-Filter-Rule attribute ([RFC4849]), this approach does not
problem of sending large amounts of data from a RADIUS Server to a entirely solve the problem of sending large amounts of data from a
RADIUS Client, as many current RADIUS attributes are not permitted RADIUS Server to a RADIUS Client, as many current RADIUS
in an Access-Challenge packets. attributes are not permitted in Access-Challenge packets.
o The second approach (utilization of names rather than values) is o The second approach (utilization of names rather than values) is
not usable either, as using names rather than values is difficult not usable either, as using names rather than values is difficult
when the nature of the data to be sent is highly dynamic (e.g. when the nature of the data to be sent is highly dynamic (e.g., a
SAML statement or NAS-Filter-Rule attributes). URLs could be used SAML statement or NAS-Filter-Rule attributes). URLs could be used
as a pointer to the location of the actual data, but their use as a pointer to the location of the actual data, but their use
would require them to be (a) dynamically created and modified, (b) would require them to be (a) dynamically created and modified,
securely accessed and (c) accessible from remote systems. (b) securely accessed, and (c) accessible from remote systems.
Satisfying these constraints would require the modification of Satisfying these constraints would require the modification of
several networking systems (e.g. firewalls and web servers). several networking systems (e.g., firewalls and web servers).
Furthermore, the setup of an additional trust infrastructure (e.g. Furthermore, the setup of an additional trust infrastructure
Public Key Infrastructure - PKI) would be required to allow secure (e.g., Public Key Infrastructure (PKI)) would be required to allow
retrieving of the information from the web server. secure retrieval of the information from the web server.
o PMTU discovery does not solve the problem, as it does not allow to o PMTU discovery does not solve the problem, as it does not allow
send data larger than the minimum of (PMTU or 4096) octets. the sending of data larger than the minimum of (PMTU or 4096)
bytes.
This document provides a mechanism to allow RADIUS peers to exchange This document provides a mechanism to allow RADIUS peers to exchange
large amounts of authorization data exceeding the 4096 octet limit, large amounts of authorization data exceeding the 4096-byte limit by
by fragmenting it across several exchanges. The proposed solution fragmenting it across several exchanges. The proposed solution does
does not impose any additional requirements to the RADIUS system not impose any additional requirements to the RADIUS system
administrators (e.g. need to modify firewall rules, set up web administrators (e.g., need to modify firewall rules, set up web
servers, configure routers, or modify any application server). It servers, configure routers, or modify any application server). It
maintains compatibility with intra-packet fragmentation mechanisms maintains compatibility with intra-packet fragmentation mechanisms
(like those defined in [RFC3579] or in [RFC6929]). It is also (like those defined in [RFC3579] or [RFC6929]). It is also
transparent to existing RADIUS proxies, which do not implement this transparent to existing RADIUS proxies, which do not implement this
specification. The only systems needing to implement this RFC are specification. The only systems needing to implement this RFC are
the ones which either generate, or consume the fragmented data being the ones that either generate or consume the fragmented data being
transmitted. Intermediate proxies just pass the packets without transmitted. Intermediate proxies just pass the packets without
changes. Nevertheless, if a proxy supports this specification, it changes. Nevertheless, if a proxy supports this specification, it
may re-assemble the data in order to either examine and/or modify it. may reassemble the data in order to examine and/or modify it.
A different approach to deal with RADIUS packets above the 4096 octet A different approach to deal with RADIUS packets above the 4096-byte
limit is described in [I-D.ietf-radext-bigger-packets], which limit is described in [RADIUS-Larger-Pkts], which proposes to extend
proposes to extend RADIUS over TCP by allowing the length field in RADIUS over TCP by allowing the Length field in the RADIUS header to
the RADIUS header to take values up to 65535 octets. This provides a take values up to 65535 bytes. This provides a simpler operation,
simpler operation, but it has the drawback of requiring every RADIUS but it has the drawback of requiring every RADIUS proxy in the path
proxy in the path between the RADIUS client and the RADIUS server to between the RADIUS Client and the RADIUS Server to implement the
implement the extension as well. extension as well.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
When these words appear in lower case, they have their natural When these words appear in lower case, they have their natural
language meaning. language meaning.
2. Status of this document 2. Status of This Document
This document is an Experimental RFC. It defines a proposal to allow This document is an Experimental RFC. It defines a proposal to allow
sending and receiving data exceeding the 4096 octet limit in RADIUS the sending and receiving of data exceeding the 4096-byte limit in
packets imposed by [RFC2865], without requiring the modification of RADIUS packets imposed by [RFC2865], without requiring the
intermediary proxies. modification of intermediary proxies.
The experiment consists in verifying whether the approach is usable The experiment consists of verifying whether the approach is usable
on a large scale environment, by observing the uptake, usability, and in a large-scale environment, by observing the uptake, usability, and
operational behavior it shows in large-scale, real-life deployments. operational behavior it shows in large-scale, real-life deployments.
In that sense, so far the main use case for this specification is the In that sense, so far the main use case for this specification is the
transportation of large SAML sentences defined within the ABFAB transportation of large SAML statements defined within the ABFAB
architecture [I-D.ietf-abfab-arch]. Hence, it can be tested wherever architecture [ABFAB-Arch]. Hence, it can be tested wherever an ABFAB
an ABFAB deployment is being piloted. deployment is being piloted.
Besides, this proposal defines some experimental features that will Besides, this proposal defines some experimental features that will
need to be tested and verified before the document can be considered need to be tested and verified before the document can be considered
for Standards Track. The first one of them is the requirement of for the Standards Track. The first one of them is the requirement of
updating [RFC2865] in order to relax the sentence defined in Section updating [RFC2865] in order to relax the sentence defined in
4.1 and stating that "An Access-Request MUST contain either a User- Section 4.1 of that document that states that "An Access-Request MUST
Password or a CHAP- Password or a State". This specification might contain either a User-Password or a CHAP-Password or a State." This
generate Access-Request packets without any of these attributes. specification might generate Access-Request packets without any of
Although all known implementations have chosen the philosophy of "be these attributes. Although all known implementations have chosen the
liberal in what you accept", we need to gain more operational philosophy of "be liberal in what you accept," we need to gain more
experience to verify that unmodified proxies do not drop this kind of operational experience to verify that unmodified proxies do not drop
packets. More details on this aspect can be found in Section 12.2. these types of packets. More details on this aspect can be found in
Section 12.2.
Another experimental feature of this specification is that it Another experimental feature of this specification is that it
requires proxies to base their routing decisions on the value of the requires proxies to base their routing decisions on the value of the
RADIUS User-Name attribute. Our experience is that this is the RADIUS User-Name attribute. Our experience is that this is the
common behaviour, thus no issues are expected. However, it needs to common behavior; thus, no issues are expected. However, it needs to
be confirmed after using different implementations of intermediate be confirmed after using different implementations of intermediate
proxies. More details on this aspect can be found in Section 12.3. proxies. More details on this aspect can be found in Section 12.3.
Moreover, this document requires two minor updates to Standards Track Moreover, this document requires two minor updates to Standards Track
documents. First, it modifies the definition of the "Reserved" field documents. First, it modifies the definition of the Reserved field
of the "Long Extended Type" attribute [RFC6929], by allocating an of the Long Extended Type attribute [RFC6929] by allocating an
additional flag "T". No issues are expected with this update, additional flag called the T (Truncation) flag. No issues are
although some proxies might drop packets that does not have the expected with this update, although some proxies might drop packets
"Reserved" field set to 0. More details on this aspect can be found that do not have the Reserved field set to 0. More details on this
in Section 12.1. aspect can be found in Section 12.1.
The other Standards Track document that requires a minor update is The other Standards Track document that requires a minor update is
[RFC6158]. It states that "attribute designers SHOULD NOT assume [RFC6158]. It states that "attribute designers SHOULD NOT assume
that a RADIUS implementation can successfully process RADIUS packets that a RADIUS implementation can successfully process RADIUS packets
larger than 4096 octets", something no longer true if this document larger than 4096 bytes," something no longer true if this document
advances. advances.
A proper "Updates" clause will be included for these modifications A proper "Updates" clause will be included for these modifications
when/if the experiment is successful and this document is re-issued when/if the experiment is successful and this document is reissued as
as a Standards Track document. a Standards Track document.
3. Scope of this document 3. Scope of This Document
This specification describes how a RADIUS Client and a RADIUS Server This specification describes how a RADIUS Client and a RADIUS Server
can exchange data exceeding the 4096 octet limit imposed by one can exchange data exceeding the 4096-byte limit imposed by one
packet. However, the mechanism described in this specification packet. However, the mechanism described in this specification
SHOULD NOT be used to exchange more than 100 kilo-octets of data. SHOULD NOT be used to exchange more than 100 kilobytes of data. Any
Any more than this may turn RADIUS into a generic transport protocol, more than this may turn RADIUS into a generic transport protocol,
such as TCP or SCTP, which is undesired. Experience shows that such as TCP or the Stream Control Transmission Protocol (SCTP), which
attempts to transport bulk data across the Internet with UDP will is undesirable. Experience shows that attempts to transport bulk
inevitably fail, unless they re-implement all of the behavior of TCP. data across the Internet with UDP will inevitably fail, unless these
The underlying design of RADIUS lacks the proper retransmission transport attempts reimplement all of the behavior of TCP. The
policies or congestion control mechanisms which would make it a underlying design of RADIUS lacks the proper retransmission policies
competitor to TCP. or congestion control mechanisms that would make it a competitor
of TCP.
Therefore, RADIUS/UDP transport is by design unable to transport bulk Therefore, RADIUS/UDP transport is by design unable to transport bulk
data. It is both undesired and impossible to change the protocol at data. It is both undesirable and impossible to change the protocol
this point in time. This specification is intended to allow the at this point in time. This specification is intended to allow the
transport of more than 4096 octets of data through existing RADIUS/ transport of more than 4096 bytes of data through existing RADIUS/UDP
UDP proxies. Other solutions such as RADIUS/TCP MUST be used when a proxies. Other solutions such as RADIUS/TCP MUST be used when a
"green field" deployment requires the transport of bulk data. "green field" deployment requires the transport of bulk data.
Section 7, below, describes with further details the reasoning for Section 7, below, describes in further detail what is considered to
this limitation, and recommends administrators to adjust it according be a reasonable amount of data and recommends that administrators
to the specific capabilities of their existing systems in terms of adjust limitations on data transfer according to the specific
memory and processing power. capabilities of their existing systems in terms of memory and
processing power.
Moreover, its scope is limited to the exchange of authorization data, Moreover, its scope is limited to the exchange of authorization data,
as other exchanges do not require of such a mechanism. In as other exchanges do not require such a mechanism. In particular,
particular, authentication exchanges have already been defined to authentication exchanges have already been defined to overcome this
overcome this limitation (e.g. RADIUS-EAP). Moreover, as they limitation (e.g., RADIUS-EAP). Moreover, as they represent the most
represent the most critical part of a RADIUS conversation, it is critical part of a RADIUS conversation, it is preferable to not
preferable to not introduce any modification to their operation that introduce into their operation any modification that may affect
may affect existing equipment. existing equipment.
There is no need to fragment accounting packets either. While the There is no need to fragment accounting packets either. While the
accounting process can send large amounts of data, that data is accounting process can send large amounts of data, that data is
typically composed of many small updates. That is, there is no typically composed of many small updates. That is, there is no
demonstrated need to send indivisible blocks of more than 4 kilo- demonstrated need to send indivisible blocks of more than 4 kilobytes
octets of data. The need to send large amounts of data per user of data. The need to send large amounts of data per user session
session often originates from the need for flow-based accounting. In often originates from the need for flow-based accounting. In this
this use-case, the RADIUS Client may send accounting data for many use case, the RADIUS Client may send accounting data for many
thousands of flows, where all those flows are tied to one user thousands of flows, where all those flows are tied to one user
session. The existing Acct-Multi-Session-Id attribute defined in session. The existing Acct-Multi-Session-Id attribute defined in
[RFC2866] Section 5.11 has been proven to work here. [RFC2866], Section 5.11 has been proven to work here.
Similarly, there is no need to fragment Change of Authorization (CoA) Similarly, there is no need to fragment Change-of-Authorization (CoA)
[RFC5176] packets. Instead, according to [RFC5176] the CoA client [RFC5176] packets. Instead, according to [RFC5176], the CoA client
will send a CoA-Request packet containing session identification will send a CoA-Request packet containing session identification
attributes, along with Service-Type = Additional-Authorization, and a attributes, along with Service-Type = Additional-Authorization, and a
State attribute. Implementations not supporting fragmentation will State attribute. Implementations not supporting fragmentation will
respond with a CoA-NAK, and an Error-Cause of Unsupported-Service. respond with a CoA-NAK and an Error-Cause of Unsupported-Service.
The above requirement does not assume that the CoA client and the The above requirement does not assume that the CoA client and the
RADIUS Server are co-located. They may, in fact be run on separate RADIUS Server are co-located. They may, in fact, be run on separate
parts of the infrastructure, or even by separate administrators. parts of the infrastructure, or even by separate administrators.
There is, however, a requirement that the two communicate. We can There is, however, a requirement that the two communicate. We can
see that the CoA client needs to send session identification see that the CoA client needs to send session identification
attributes in order to send CoA packets. These attributes cannot be attributes in order to send CoA packets. These attributes cannot be
known a priori by the CoA client, and can only come from the RADIUS known a priori by the CoA client and can only come from the RADIUS
Server. Therefore, even when the two systems are not co-located, Server. Therefore, even when the two systems are not co-located,
they must be able to communicate in order to operate in unison. The they must be able to communicate in order to operate in unison. The
alternative is for the two systems to have differing views of the alternative is for the two systems to have differing views of the
users authorization parameters, which is a security disaster. users' authorization parameters; such a scenario would be a security
disaster.
This specification does not allow for fragmentation of CoA packets. This specification does not allow for fragmentation of CoA packets.
Allowing for fragmented CoA packets would involve changing multiple Allowing for fragmented CoA packets would involve changing multiple
parts of the RADIUS protocol, with the corresponding possibility for parts of the RADIUS protocol; such changes introduce the risk of
implementation issues, mistakes, etc. implementation issues, mistakes, etc.
Where CoA clients (i.e. RADIUS Servers) need to send large amounts Where CoA clients (i.e., RADIUS Servers) need to send large amounts
of authorization data to a CoA server (i.e. RADIUS Client), they of authorization data to a CoA server (i.e., RADIUS Client), they
need only send a minimal CoA-Request packet, containing Service-Type need only send a minimal CoA-Request packet containing a Service-Type
of Authorize-Only, as per [RFC5176], along with session of Authorize Only, as per [RFC5176], along with session
identification attributes. This CoA packet serves as a signal to the identification attributes. This CoA packet serves as a signal to the
RADIUS Client that the users' session requires re-authorization. RADIUS Client that the users' session requires re-authorization.
When the RADIUS Client re-authorizes the user via Access-Request, the When the RADIUS Client re-authorizes the user via Access-Request, the
RADIUS Server can perform fragmentation, and send large amounts of RADIUS Server can perform fragmentation and send large amounts of
authorization data to the RADIUS Client. authorization data to the RADIUS Client.
The assumption in the above scenario is that the CoA client and The assumption in the above scenario is that the CoA client and
RADIUS Server are co-located, or at least strongly coupled. That is, RADIUS Server are co-located, or at least strongly coupled. That is,
the path from CoA client to CoA server SHOULD be the exact reverse of the path from CoA client to CoA server SHOULD be the exact reverse of
the path from RADIUS Client to RADIUS Server. The following diagram the path from RADIUS Client to RADIUS Server. The following diagram
will hopefully clarify the roles: will hopefully clarify the roles:
+----------------+ +----------------+
| RADIUS CoA | | RADIUS CoA |
| Client Server | | Client Server |
+----------------+ +----------------+
| ^ | ^
Access-Request | | CoA-Request Access-Request | | CoA-Request
v | v |
+----------------+ +----------------+
| RADIUS CoA | | RADIUS CoA |
| Server Client | | Server Client |
+----------------+ +----------------+
Where there is a proxy involved: Where there is a proxy involved:
+----------------+ +----------------+
| RADIUS CoA | | RADIUS CoA |
| Client Server | | Client Server |
+----------------+ +----------------+
| ^ | ^
Access-Request | | CoA-Request Access-Request | | CoA-Request
v | v |
+----------------+ +----------------+
| RADIUS CoA | | RADIUS CoA |
| Proxy Proxy | | Proxy Proxy |
+----------------+ +----------------+
| ^ | ^
Access-Request | | CoA-Request Access-Request | | CoA-Request
v | v |
+----------------+ +----------------+
| RADIUS CoA | | RADIUS CoA |
| Server Client | | Server Client |
+----------------+ +----------------+
That is, the RADIUS and CoA subsystems at each hop are strongly That is, the RADIUS and CoA subsystems at each hop are strongly
connected. Where they are not strongly connected, it will be connected. Where they are not strongly connected, it will be
impossible to use CoA-Request packets to transport large amounts of impossible to use CoA-Request packets to transport large amounts of
authorization data. authorization data.
This design is more complicated than allowing for fragmented CoA This design is more complicated than allowing for fragmented CoA
packets. However, the CoA client and the RADIUS Server must packets. However, the CoA client and the RADIUS Server must
communicate even when not using this specification. We believe that communicate even when not using this specification. We believe that
standardizing that communication, and using one method for exchange standardizing that communication and using one method for exchange of
of large data is preferred to unspecified communication methods and large data are preferred to unspecified communication methods and
multiple ways of achieving the same result. If we were to allow multiple ways of achieving the same result. If we were to allow
fragmentation of data over CoA packets, the size and complexity of fragmentation of data over CoA packets, the size and complexity of
this specification would increase significantly. this specification would increase significantly.
The above requirement solves a number of issues. It clearly The above requirement solves a number of issues. It clearly
separates session identification from authorization. Without this separates session identification from authorization. Without this
separation, it is difficult to both identify a session, and change separation, it is difficult to both identify a session and change its
its authorization using the same attribute. It also ensures that the authorization using the same attribute. It also ensures that the
authorization process is the same for initial authentication, and for authorization process is the same for initial authentication and
CoA. for CoA.
4. Overview 4. Overview
Authorization exchanges can occur either before or after end user Authorization exchanges can occur either before or after end-user
authentication has been completed. An authorization exchange before authentication has been completed. An authorization exchange before
authentication allows a RADIUS Client to provide the RADIUS Server authentication allows a RADIUS Client to provide the RADIUS Server
with information that MAY modify how the authentication process will with information that MAY modify how the authentication process will
be performed (e.g. it may affect the selection of the EAP method). be performed (e.g., it may affect the selection of the EAP method).
An authorization exchange after authentication allows the RADIUS An authorization exchange after authentication allows the RADIUS
Server to provide the RADIUS Client with information about the end Server to provide the RADIUS Client with information about the end
user, the results of the authentication process and/or obligations to user, the results of the authentication process, and/or obligations
be enforced. In this specification we refer to the "pre- to be enforced. In this specification, we refer to
authorization" as the exchange of authorization information before "pre-authorization" as the exchange of authorization information
the end user authentication has started (from the RADIUS Client to before the end-user authentication has started (from the RADIUS
the RADIUS Server), whereas the term "post-authorization" is used to Client to the RADIUS Server), whereas the term "post-authorization"
refer to an authorization exchange happening after this is used to refer to an authorization exchange happening after this
authentication process (from the RADIUS Server to the RADIUS Client). authentication process (from the RADIUS Server to the RADIUS Client).
In this specification we refer to the "size limit" as the practical In this specification, we refer to the "size limit" as the practical
limit on RADIUS packet sizes. This limit is the minimum between 4096 limit on RADIUS packet sizes. This limit is the minimum between
octets and the current PMTU. We define below a method which uses 4096 bytes and the current PMTU. We define below a method that uses
Access-Request and Access-Accept in order to exchange fragmented Access-Request and Access-Accept in order to exchange fragmented
data. The RADIUS Client and server exchange a series of Access- data. The RADIUS Client and Server exchange a series of
Request / Access-Accept packets, until such time as all of the Access-Request / Access-Accept packets, until such time as all of the
fragmented data has been transported. Each packet contains a Frag- fragmented data has been transported. Each packet contains a
Status attribute which lets the other party know if fragmentation is Frag-Status attribute, which lets the other party know if
desired, ongoing, or finished. Each packet may also contain the fragmentation is desired, ongoing, or finished. Each packet may also
fragmented data, or instead be an "ACK" to a previous fragment from contain the fragmented data or may instead be an "ACK" to a previous
the other party. Each Access-Request contains a User-Name attribute, fragment from the other party. Each Access-Request contains a
allowing the packet to be proxied if necessary (see Section 11.1). User-Name attribute, allowing the packet to be proxied if necessary
Each Access-Request may also contain a State attribute, which serves (see Section 11.1). Each Access-Request may also contain a State
to tie it to a previous Access-Accept. Each Access-Accept contains a attribute, which serves to tie it to a previous Access-Accept. Each
State attribute, for use by the RADIUS Client in a later Access- Access-Accept contains a State attribute, for use by the RADIUS
Request. Each Access-Accept contains a Service-Type attribute with Client in a later Access-Request. Each Access-Accept contains a
the "Additional-Authorization" value. This indicates that the Service-Type attribute with the "Additional-Authorization" value.
service being provided is part of a fragmented exchange, and that the This indicates that the service being provided is part of a
Access-Accept should not be interpreted as providing network access fragmented exchange and that the Access-Accept should not be
to the end user. interpreted as providing network access to the end user.
When a RADIUS Client or RADIUS Server need to send data that exceeds When a RADIUS Client or RADIUS Server needs to send data that exceeds
the size limit, the mechanism proposed in this document is used. the size limit, the mechanism proposed in this document is used.
Instead of encoding one large RADIUS packet, a series of smaller Instead of encoding one large RADIUS packet, a series of smaller
RADIUS packets of the same type are encoded. Each smaller packet is RADIUS packets of the same type are encoded. Each smaller packet is
called a "chunk" in this specification, in order to distinguish it called a "chunk" in this specification, in order to distinguish it
from traditional RADIUS packets. The encoding process is a simple from traditional RADIUS packets. The encoding process is a simple
linear walk over the attributes to be encoded. This walk preserves linear walk over the attributes to be encoded. This walk preserves
the order of the attributes of the same type, as required by the order of the attributes of the same type, as required by
[RFC2865]. The number of attributes encoded in a particular chunk [RFC2865]. The number of attributes encoded in a particular chunk
depends on the size limit, the size of each attribute, the number of depends on the size limit, the size of each attribute, the number of
proxies between the RADIUS Client and RADIUS Server, and the overhead proxies between the RADIUS Client and RADIUS Server, and the overhead
for fragmentation signalling attributes. Specific details are given for fragmentation-signaling attributes. Specific details are given
in Section 6. A new attribute called Frag-Status (Section 10.1) in Section 6. A new attribute called Frag-Status (Section 10.1)
signals the fragmentation status. signals the fragmentation status.
After the first chunk is encoded, it is sent to the other party. The After the first chunk is encoded, it is sent to the other party. The
packet is identified as a chunk via the Frag-Status attribute. The packet is identified as a chunk via the Frag-Status attribute. The
other party then requests additional chunks, again using the Frag- other party then requests additional chunks, again using the
Status attribute. This process is repeated until all the attributes Frag-Status attribute. This process is repeated until all the
have been sent from one party to the other. When all the chunks have attributes have been sent from one party to the other. When all the
been received, the original list of attributes is reconstructed and chunks have been received, the original list of attributes is
processed as if it had been received in one packet. reconstructed and processed as if it had been received in one packet.
The reconstruction process is performed by simply appending all of The reconstruction process is performed by simply appending all of
the chunks together. Unlike IPv4 fragmentation, there is no the chunks together. Unlike IPv4 fragmentation, there is no Fragment
"fragment offset" field. The chunks in this specification are Offset field. The chunks in this specification are explicitly
explicitly ordered, as RADIUS is a lock-step protocol, as noted in ordered, as RADIUS is a lock-step protocol, as noted in Section 12.4.
Section Section 12.4. That is, chunk N+1 cannot be sent until all of That is, chunk N+1 cannot be sent until all of the chunks up to and
the chunks up to and including N have been received and acknowledged. including N have been received and acknowledged.
When multiple chunks are sent, a special situation may occur for When multiple chunks are sent, a special situation may occur for Long
Extended Type attributes as defined in [RFC6929]. The fragmentation Extended Type attributes as defined in [RFC6929]. The fragmentation
process may split a fragmented attribute across two or more chunks, process may split a fragmented attribute across two or more chunks,
which is not permitted by that specification. We address this issue which is not permitted by that specification. We address this issue
by using the newly defined flag "T" in the Reserved field of the by using the newly defined T flag in the Reserved field of the Long
"Long Extended Type" attribute format (see Section 9 for further Extended Type attribute format (see Section 9 for further details on
details on this flag). this flag).
This last situation is expected to be the most common occurrence in This last situation is expected to be the most common occurrence in
chunks. Typically, packet fragmentation will occur as a consequence chunks. Typically, packet fragmentation will occur as a consequence
of a desire to send one or more large (and therefore fragmented) of a desire to send one or more large (and therefore fragmented)
attributes. The large attribute will likely be split into two or attributes. The large attribute will likely be split into two or
more pieces. Where chunking does not split a fragmented attribute, more pieces. Where chunking does not split a fragmented attribute,
no special treatment is necessary. no special treatment is necessary.
The setting of the "T" flag is the only case where the chunking The setting of the T flag is the only case where the chunking process
process affects the content of an attribute. Even then, the "Value" affects the content of an attribute. Even then, the Value fields of
fields of all attributes remain unchanged. Any per-packet security all attributes remain unchanged. Any per-packet security attributes,
attributes such as Message-Authenticator are calculated for each such as Message-Authenticator, are calculated for each chunk
chunk independently. There are neither integrity nor security checks independently. Neither integrity checks nor security checks are
performed on the "original" packet. performed on the "original" packet.
Each RADIUS packet sent or received as part of the chunking process Each RADIUS packet sent or received as part of the chunking process
MUST be a valid packet, subject to all format and security MUST be a valid packet, subject to all format and security
requirements. This requirement ensures that a "transparent" proxy requirements. This requirement ensures that a "transparent" proxy
not implementing this specification can receive and send compliant not implementing this specification can receive and send compliant
packets. That is, a proxy which simply forwards packets without packets. That is, a proxy that simply forwards packets without
detailed examination or any modification will be able to proxy detailed examination or any modification will be able to proxy
"chunks". "chunks".
5. Fragmentation of packets 5. Fragmentation of Packets
When the RADIUS Client or the RADIUS Server desires to send a packet When the RADIUS Client or the RADIUS Server desires to send a packet
that exceeds the size limit, it is split into chunks and sent via that exceeds the size limit, it is split into chunks and sent via
multiple client/server exchanges. The exchange is indicated via the multiple client/server exchanges. The exchange is indicated via the
Frag-Status attribute, which has value More-Data-Pending for all but Frag-Status attribute, which has value More-Data-Pending for all but
the last chunk of the series. The chunks are tied together via the the last chunk of the series. The chunks are tied together via the
State attribute. State attribute.
The delivery of a large fragmented RADIUS packet with authorization The delivery of a large fragmented RADIUS packet with authorization
data can happen before or after the end user has been authenticated data can happen before or after the end user has been authenticated
skipping to change at page 12, line 41 skipping to change at page 13, line 30
large packet with authorization information to the RADIUS Server large packet with authorization information to the RADIUS Server
before the end user is authenticated. Only the RADIUS Client is before the end user is authenticated. Only the RADIUS Client is
allowed to send authorization data during this phase. allowed to send authorization data during this phase.
2. Post-authorization. In this phase, the RADIUS Server MAY send a 2. Post-authorization. In this phase, the RADIUS Server MAY send a
large packet with authorization data to the RADIUS Client after large packet with authorization data to the RADIUS Client after
the end user has been authenticated. Only the RADIUS Server is the end user has been authenticated. Only the RADIUS Server is
allowed to send authorization data during this phase. allowed to send authorization data during this phase.
The following subsections describe how to perform fragmentation for The following subsections describe how to perform fragmentation for
packets for these two phases, pre-authorization and post- packets for these two phases. We give the packet type, along with a
authorization. We give the packet type, along with a RADIUS RADIUS Identifier, to indicate that requests and responses are
Identifier, to indicate that requests and responses are connected. connected. We then give a list of attributes. We do not give values
We then give a list of attributes. We do not give values for most for most attributes, as we wish to concentrate on the fragmentation
attributes, as we wish to concentrate on the fragmentation behaviour, behavior rather than packet contents. Attribute values are given for
rather than packet contents. Attribute values are given for
attributes relevant to the fragmentation process. Where "long attributes relevant to the fragmentation process. Where "long
extended" attributes are used, we indicate the M (More) and T extended" attributes are used, we indicate the M (More) and T
(Truncation) flags as optional square brackets after the attribute (Truncation) flags as optional square brackets after the attribute
name. As no "long extended" attributes have yet been defined, we use name. As no "long extended" attributes have yet been defined, we use
example attributes, named as "Example-Long-1", etc. The maximum example attributes, named as "Example-Long-1", etc. For the sake of
chunk size is established in term of number of attributes (11), for simplicity, the maximum chunk size is established in terms of the
sake of simplicity. number of attributes (11).
5.1. Pre-authorization 5.1. Pre-Authorization
When the RADIUS Client needs to send a large amount of data to the When the RADIUS Client needs to send a large amount of data to the
RADIUS Server, the data to be sent is split into chunks and sent to RADIUS Server, the data to be sent is split into chunks and sent to
the RADIUS Server via multiple Access-Request / Access-Accept the RADIUS Server via multiple Access-Request / Access-Accept
exchanges. The example below shows this exchange. exchanges. The example below shows this exchange.
The following is an Access-Request which the RADIUS Client intends to The following is an Access-Request that the RADIUS Client intends to
send to a RADIUS Server. However, due to a combination of issues send to a RADIUS Server. However, due to a combination of issues
(PMTU, large attributes, etc.), the content does not fit into one (PMTU, large attributes, etc.), the content does not fit into one
Access-Request packet. Access-Request packet.
Access-Request Access-Request
User-Name User-Name
NAS-Identifier NAS-Identifier
Calling-Station-Id Calling-Station-Id
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
skipping to change at page 13, line 42 skipping to change at page 14, line 39
Example-Long-1 Example-Long-1
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 Example-Long-2
Figure 1: Desired Access-Request Figure 1: Desired Access-Request
The RADIUS Client therefore must send the attributes listed above in The RADIUS Client therefore must send the attributes listed above in
a series of chunks. The first chunk contains eight (8) attributes a series of chunks. The first chunk contains eight (8) attributes
from the original Access-Request, and a Frag-Status attribute. Since from the original Access-Request, and a Frag-Status attribute. Since
last attribute is "Example-Long-1" with the "M" flag set, the the last attribute is "Example-Long-1" with the M flag set, the
chunking process also sets the "T" flag in that attribute. The chunking process also sets the T flag in that attribute. The
Access-Request is sent with a RADIUS Identifier field having value Access-Request is sent with a RADIUS Identifier field having
23. The Frag-Status attribute has value More-Data-Pending, to value 23. The Frag-Status attribute has value More-Data-Pending, to
indicate that the RADIUS Client wishes to send more data in a indicate that the RADIUS Client wishes to send more data in a
subsequent Access-Request. The RADIUS Client also adds a Service- subsequent Access-Request. The RADIUS Client also adds a
Type attribute, which indicates that it is part of the chunking Service-Type attribute, which indicates that it is part of the
process. The packet is signed with the Message-Authenticator chunking process. The packet is signed with the
attribute, completing the maximum number of attributes (11). Message-Authenticator attribute, completing the maximum number of
attributes (11).
Access-Request (ID = 23) Access-Request (ID = 23)
User-Name User-Name
NAS-Identifier NAS-Identifier
Calling-Station-Id Calling-Station-Id
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [MT] Example-Long-1 [MT]
Frag-Status = More-Data-Pending Frag-Status = More-Data-Pending
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
Message-Authenticator Message-Authenticator
Figure 2: Access-Request (chunk 1) Figure 2: Access-Request (Chunk 1)
Compliant RADIUS Servers (i.e. servers implementing fragmentation) Compliant RADIUS Servers (i.e., servers implementing fragmentation)
receiving this packet will see the Frag-Status attribute, and receiving this packet will see the Frag-Status attribute and will
postpone all authorization and authentication handling until all of postpone all authorization and authentication handling until all of
the chunks have been received. This postponement also affects to the the chunks have been received. This postponement also applies to the
verification that the Access-Request packet contains some kind of verification that the Access-Request packet contains some kind of
authentication attribute (e.g. User-Password, CHAP-Password, State authentication attribute (e.g., User-Password, CHAP-Password, State,
or other future attribute), as required by [RFC2865] (see or other future attribute), as required by [RFC2865] (see
Section 12.2 for more information on this). Section 12.2 for more information on this).
Non-compliant RADIUS Servers (i.e. servers not implementing Non-compliant RADIUS Servers (i.e., servers not implementing
fragmentation) should also see the Service-Type requesting fragmentation) should also see the Service-Type requesting
provisioning for an unknown service, and return Access-Reject. Other provisioning for an unknown service and return Access-Reject. Other
non-compliant RADIUS Servers may return an Access-Reject, Access- non-compliant RADIUS Servers may return an Access-Reject or
Challenge, or an Access-Accept with a particular Service-Type other Access-Challenge, or they may return an Access-Accept with a
than Additional-Authorization. Compliant RADIUS Client particular Service-Type other than Additional-Authorization.
implementations MUST treat these responses as if they had received Compliant RADIUS Client implementations MUST treat these responses as
Access-Reject instead. if they had received Access-Reject instead.
Compliant RADIUS Servers who wish to receive all of the chunks will Compliant RADIUS Servers who wish to receive all of the chunks will
respond with the following packet. The value of the State here is respond with the following packet. The value of the State here is
arbitrary, and serves only as a unique token for example purposes. arbitrary and serves only as a unique token for example purposes. We
We only note that it MUST be temporally unique to the RADIUS Server. only note that it MUST be temporally unique to the RADIUS Server.
Access-Accept (ID = 23) Access-Accept (ID = 23)
Frag-Status = More-Data-Request Frag-Status = More-Data-Request
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
State = 0xabc00001 State = 0xabc00001
Message-Authenticator Message-Authenticator
Figure 3: Access-Accept (chunk 1) Figure 3: Access-Accept (Chunk 1)
The RADIUS Client will see this response, and use the RADIUS The RADIUS Client will see this response and use the RADIUS
Identifier field to associate it with an ongoing chunking session. Identifier field to associate it with an ongoing chunking session.
Compliant RADIUS Clients will then continue the chunking process.
Compliant NASes will then continue the chunking process. Non- Non-compliant RADIUS Clients will never see a response such as this,
compliant NASes will never see a response such as this, as they will as they will never send a Frag-Status attribute. The Service-Type
never send a Frag-Status attribute. The Service-Type attribute is attribute is included in the Access-Accept in order to signal that
included in the Access-Accept in order to signal that the response is the response is part of the chunking process. This packet therefore
part of the chunking process. This packet therefore does not does not provision any network service for the end user.
provision any network service for the end user.
The RADIUS Client continues the process by sending the next chunk, The RADIUS Client continues the process by sending the next chunk,
which includes an additional six (6) attributes from the original which includes an additional six (6) attributes from the original
packet. It again includes the User-Name attribute, so that non- packet. It again includes the User-Name attribute, so that
compliant proxies can process the packet (see Section 11.1). It sets non-compliant proxies can process the packet (see Section 11.1). It
the Frag-Status attribute to More-Data-Pending, as more data is sets the Frag-Status attribute to More-Data-Pending, as more data is
pending. It includes a Service-Type for reasons described above. It pending. It includes a Service-Type, for the reasons described
includes the State attribute from the previous Access-accept. It above. It includes the State attribute from the previous
signs the packet with Message-Authenticator, as there are no Access-Accept. It signs the packet with Message-Authenticator, as
authentication attributes in the packet. It uses a new RADIUS there are no authentication attributes in the packet. It uses a new
Identifier field. RADIUS Identifier field.
Access-Request (ID = 181) Access-Request (ID = 181)
User-Name User-Name
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 Example-Long-1
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 [MT] Example-Long-2 [MT]
Frag-Status = More-Data-Pending Frag-Status = More-Data-Pending
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
State = 0xabc000001 State = 0xabc000001
Message-Authenticator Message-Authenticator
Figure 4: Access-Request (chunk 2) Figure 4: Access-Request (Chunk 2)
Compliant RADIUS Servers receiving this packet will see the Frag- Compliant RADIUS Servers receiving this packet will see the
Status attribute, and look for a State attribute. Since one exists Frag-Status attribute and look for a State attribute. Since one
and it matches a State sent in an Access-Accept, this packet is part exists and it matches a State sent in an Access-Accept, this packet
of a chunking process. The RADIUS Server will associate the is part of a chunking process. The RADIUS Server will associate the
attributes with the previous chunk. Since the Frag-Status attribute attributes with the previous chunk. Since the Frag-Status attribute
has value More-Data-Request, the RADIUS Server will respond with an has value More-Data-Request, the RADIUS Server will respond with an
Access-Accept as before. It MUST include a State attribute, with a Access-Accept as before. It MUST include a State attribute, with a
value different from the previous Access-Accept. This State MUST value different from the previous Access-Accept. This State MUST
again be globally and temporally unique. again be globally and temporally unique.
Access-Accept (ID = 181) Access-Accept (ID = 181)
Frag-Status = More-Data-Request Frag-Status = More-Data-Request
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
State = 0xdef00002 State = 0xdef00002
Message-Authenticator Message-Authenticator
Figure 5: Access-Accept (chunk 2) Figure 5: Access-Accept (Chunk 2)
The RADIUS Client will see this response, and use the RADIUS The RADIUS Client will see this response and use the RADIUS
Identifier field to associate it with an ongoing chunking session. Identifier field to associate it with an ongoing chunking session.
The RADIUS Client continues the chunking process by sending the next The RADIUS Client continues the chunking process by sending the next
chunk, with the final attribute(s) from the original packet, and chunk, with the final attribute(s) from the original packet, and
again includes the original User-Name attribute. The Frag-Status again includes the original User-Name attribute. The Frag-Status
attribute is not included in the next Access-Request, as no more attribute is not included in the next Access-Request, as no more
chunks are available for sending. The RADIUS Client includes the chunks are available for sending. The RADIUS Client includes the
State attribute from the previous Access-accept. It signs the packet State attribute from the previous Access-Accept. It signs the packet
with Message-Authenticator, as there are no authentication attributes with Message-Authenticator, as there are no authentication attributes
in the packet. It again uses a new RADIUS Identifier field. in the packet. It again uses a new RADIUS Identifier field.
Access-Request (ID = 241) Access-Request (ID = 241)
User-Name User-Name
Example-Long-2 Example-Long-2
State = 0xdef00002 State = 0xdef00002
Message-Authenticator Message-Authenticator
Figure 6: Access-Request (chunk 3) Figure 6: Access-Request (Chunk 3)
On reception of this last chunk, the RADIUS Server matches it with an On reception of this last chunk, the RADIUS Server matches it with an
ongoing session via the State attribute, and sees that there is no ongoing session via the State attribute and sees that there is no
Frag-Status attribute present. It then processes the received Frag-Status attribute present. It then processes the received
attributes as if they had been sent in one RADIUS packet. See attributes as if they had been sent in one RADIUS packet. See
Section 8.4 for further details of this process. It generates the Section 8.4 for further details on this process. It generates the
appropriate response, which can be either Access-Accept or Access- appropriate response, which can be either Access-Accept or
Reject. In this example, we show an Access-Accept. The RADIUS Access-Reject. In this example, we show an Access-Accept. The
Server MUST send a State attribute, which permits link the received RADIUS Server MUST send a State attribute, which allows linking the
data with the authentication process. received data with the authentication process.
Access-Accept (ID = 241) Access-Accept (ID = 241)
State = 0x98700003 State = 0x98700003
Message-Authenticator Message-Authenticator
Figure 7: Access-Accept (chunk 3) Figure 7: Access-Accept (Chunk 3)
The above example shows in practice how the chunking process works. The above example shows in practice how the chunking process works.
We re-iterate the implementation and security requirements here. We reiterate the implementation and security requirements here.
Each chunk is a valid RADIUS packet (see Section 12.2 for some Each chunk is a valid RADIUS packet (see Section 12.2 for some
considerations about this), and all RADIUS format and security considerations about this), and all RADIUS format and security
requirements MUST be followed before any chunking process is applied. requirements MUST be followed before any chunking process is applied.
Every chunk except for the last one from a RADIUS Client MUST include Every chunk except for the last one from a RADIUS Client MUST include
a Frag-Status attribute, with value More-Data-Pending. The last a Frag-Status attribute, with value More-Data-Pending. The last
chunk MUST NOT contain a Frag-Status attribute. Each chunk except chunk MUST NOT contain a Frag-Status attribute. Each chunk except
for the last from a RADIUS Client MUST include a Service-Type for the last one from a RADIUS Client MUST include a Service-Type
attribute, with value Additional-Authorization. Each chunk MUST attribute, with value Additional-Authorization. Each chunk MUST
include a User-Name attribute, which MUST be identical in all chunks. include a User-Name attribute, which MUST be identical in all chunks.
Each chunk except for the first one from a RADIUS Client MUST include Each chunk except for the first one from a RADIUS Client MUST include
a State attribute, which MUST be copied from a previous Access- a State attribute, which MUST be copied from a previous
Accept. Access-Accept.
Each Access-Accept MUST include a State attribute. The value for Each Access-Accept MUST include a State attribute. The value for
this attribute MUST change in every new Access-Accept, and MUST be this attribute MUST change in every new Access-Accept and MUST be
globally and temporally unique. globally and temporally unique.
5.2. Post-authorization 5.2. Post-Authorization
When the RADIUS Server wants to send a large amount of authorization When the RADIUS Server wants to send a large amount of authorization
data to the RADIUS Client after authentication, the operation is very data to the RADIUS Client after authentication, the operation is very
similar to the pre-authorization one. The presence of Service-Type = similar to the pre-authorization process. The presence of a
Additional-Authorization attribute ensures that a RADIUS Client not Service-Type = Additional-Authorization attribute ensures that a
supporting this specification will treat that unrecognized Service- RADIUS Client not supporting this specification will treat that
Type as though an Access-Reject had been received instead ([RFC2865] unrecognized Service-Type as though an Access-Reject had been
Section 5.6). If the original large Access-Accept packet contained a received instead ([RFC2865], Section 5.6). If the original large
Service-Type attribute, it will be included with its original value Access-Accept packet contained a Service-Type attribute, it will be
in the last transmitted chunk, to avoid confusion with the one used included with its original value in the last transmitted chunk, to
for fragmentation signalling. It is RECOMMENDED that RADIUS Servers avoid confusion with the one used for fragmentation signaling. It is
include a State attribute on their original Access-Accept packets, RECOMMENDED that RADIUS Servers include a State attribute in their
even if fragmentation is not taking place, to allow the RADIUS Client original Access-Accept packets, even if fragmentation is not taking
to send additional authorization data in subsequent exchanges. This place, to allow the RADIUS Client to send additional authorization
State attribute would be included in the last transmitted chunk, to data in subsequent exchanges. This State attribute would be included
avoid confusion with the ones used for fragmentation signalling. in the last transmitted chunk, to avoid confusion with the ones used
for fragmentation signaling.
Client supporting this specification MUST include a Frag-Status = Clients supporting this specification MUST include a Frag-Status =
Fragmentation-Supported attribute in the first Access-Request sent to Fragmentation-Supported attribute in the first Access-Request sent to
the RADIUS Server, in order to indicate they would accept fragmented the RADIUS Server, in order to indicate that they would accept
data from the sever. This is not required if pre-authorization fragmented data from the server. This is not required if the
process was carried out, as it is implicit. pre-authorization process was carried out, as it is implicit.
The following is an Access-Accept which the RADIUS Server intends to The following is an Access-Accept that the RADIUS Server intends to
send to a RADIUS Client. However, due to a combination of issues send to a RADIUS Client. However, due to a combination of issues
(PMTU, large attributes, etc.), the content does not fit into one (PMTU, large attributes, etc.), the content does not fit into one
Access-Accept packet. Access-Accept packet.
Access-Accept Access-Accept
User-Name User-Name
EAP-Message EAP-Message
Service-Type(Login) Service-Type = Login
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 Example-Long-1
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 Example-Long-2
State = 0xcba00003 State = 0xcba00003
Figure 8: Desired Access-Accept Figure 8: Desired Access-Accept
The RADIUS Server therefore must send the attributes listed above in The RADIUS Server therefore must send the attributes listed above in
a series of chunks. The first chunk contains seven (7) attributes a series of chunks. The first chunk contains seven (7) attributes
from the original Access-Accept, and a Frag-Status attribute. Since from the original Access-Accept, and a Frag-Status attribute. Since
last attribute is "Example-Long-1" with the "M" flag set, the the last attribute is "Example-Long-1" with the M flag set, the
chunking process also sets the "T" flag in that attribute. The chunking process also sets the T flag in that attribute. The
Access-Accept is sent with a RADIUS Identifier field having value 30 Access-Accept is sent with a RADIUS Identifier field having value 30,
corresponding to a previous Access-Request not depicted. The Frag- corresponding to a previous Access-Request not depicted. The
Status attribute has value More-Data-Pending, to indicate that the Frag-Status attribute has value More-Data-Pending, to indicate that
RADIUS Server wishes to send more data in a subsequent Access-Accept. the RADIUS Server wishes to send more data in a subsequent
The RADIUS Server also adds a Service-Type attribute with value Access-Accept. The RADIUS Server also adds a Service-Type attribute
Additional-Authorization, which indicates that it is part of the with value Additional-Authorization, which indicates that it is part
chunking process. Note that the original Service-Type is not of the chunking process. Note that the original Service-Type is not
included in this chunk. Finally, a State attribute is included to included in this chunk. Finally, a State attribute is included to
allow matching subsequent requests with this conversation, and the allow matching subsequent requests with this conversation, and the
packet is signed with the Message-Authenticator attribute, completing packet is signed with the Message-Authenticator attribute, completing
the maximum number of attributes of 11. the maximum number of attributes (11).
Access-Accept (ID = 30) Access-Accept (ID = 30)
User-Name User-Name
EAP-Message EAP-Message
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [MT] Example-Long-1 [MT]
Frag-Status = More-Data-Pending Frag-Status = More-Data-Pending
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
State = 0xcba00004 State = 0xcba00004
Message-Authenticator Message-Authenticator
Figure 9: Access-Accept (chunk 1) Figure 9: Access-Accept (Chunk 1)
Compliant RADIUS Clients receiving this packet will see the Frag- Compliant RADIUS Clients receiving this packet will see the
Status attribute, and suspend all authorization handling until all of Frag-Status attribute and suspend all authorization handling until
the chunks have been received. Non-compliant RADIUS Clients should all of the chunks have been received. Non-compliant RADIUS Clients
also see the Service-Type indicating the provisioning for an unknown should also see the Service-Type indicating the provisioning for an
service, and will treat it as an Access-Reject. unknown service and will treat it as an Access-Reject.
RADIUS Clients who wish to receive all of the chunks will respond RADIUS Clients who wish to receive all of the chunks will respond
with the following packet, where the value of the State attribute is with the following packet, where the value of the State attribute is
taken from the received Access-Accept. They also include the User- taken from the received Access-Accept. They will also include the
Name attribute so that non-compliant proxies can process the packet User-Name attribute so that non-compliant proxies can process the
(Section 11.1). packet (Section 11.1).
Access-Request (ID = 131) Access-Request (ID = 131)
User-Name User-Name
Frag-Status = More-Data-Request Frag-Status = More-Data-Request
Service-Type = Additional-Authorization Service-Type = Additional-Authorization
State = 0xcba00004 State = 0xcba00004
Message-Authenticator Message-Authenticator
Figure 10: Access-Request (chunk 1) Figure 10: Access-Request (Chunk 1)
The RADIUS Server receives this request, and uses the State attribute The RADIUS Server receives this request and uses the State attribute
to associate it with an ongoing chunking session. Compliant ASes to associate it with an ongoing chunking session. Compliant RADIUS
will then continue the chunking process. Non-compliant ASes will Servers will then continue the chunking process. Non-compliant
never see a response such as this, as they will never send a Frag- RADIUS Servers will never see a response such as this, as they will
Status attribute. never send a Frag-Status attribute.
The RADIUS Server continues the chunking process by sending the next The RADIUS Server continues the chunking process by sending the next
chunk, with the final attribute(s) from the original packet. The chunk, with the final attribute(s) from the original packet. The
value of the Identifier field is taken from the received Access- value of the Identifier field is taken from the received
Request. A Frag-Status attribute is not included in the next Access- Access-Request. A Frag-Status attribute is not included in the next
Accept, as no more chunks are available for sending. The RADIUS Access-Accept, as no more chunks are available for sending. The
Server includes the original State attribute to allow the RADIUS RADIUS Server includes the original State attribute to allow the
Client to send additional authorization data. The original Service- RADIUS Client to send additional authorization data. The original
Type attribute is included as well. Service-Type attribute is included as well.
Access-Accept (ID = 131) Access-Accept (ID = 131)
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 [M] Example-Long-1 [M]
Example-Long-1 Example-Long-1
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 [M] Example-Long-2 [M]
Example-Long-2 Example-Long-2
Service-Type = Login Service-Type = Login
State = 0xfda000003 State = 0xfda000003
Message-Authenticator Message-Authenticator
Figure 11: Access-Accept (chunk 2) Figure 11: Access-Accept (Chunk 2)
On reception of this last chunk, the RADIUS Client matches it with an On reception of this last chunk, the RADIUS Client matches it with an
ongoing session via the Identifier field, and sees that there is no ongoing session via the Identifier field and sees that there is no
Frag-Status attribute present. It then processes the received Frag-Status attribute present. It then processes the received
attributes as if they had been sent in one RADIUS packet. See attributes as if they had been sent in one RADIUS packet. See
Section 8.4 for further details of this process. Section 8.4 for further details on this process.
6. Chunk size 6. Chunk Size
In an ideal scenario, each intermediate chunk would be exactly the In an ideal scenario, each intermediate chunk would be exactly the
size limit in length. In this way, the number of round trips size limit in length. In this way, the number of round trips
required to send a large packet would be optimal. However, this is required to send a large packet would be optimal. However, this is
not possible for several reasons. not possible for several reasons.
1. RADIUS attributes have a variable length, and must be included 1. RADIUS attributes have a variable length and must be included
completely in a chunk. Thus, it is possible that, even if there completely in a chunk. Thus, it is possible that, even if there
is some free space in the chunk, it is not enough to include the is some free space in the chunk, it is not enough to include the
next attribute. This can generate up to 254 octets of spare next attribute. This can generate up to 254 bytes of spare space
space on every chunk. in every chunk.
2. RADIUS fragmentation requires the introduction of some extra 2. RADIUS fragmentation requires the introduction of some extra
attributes for signalling. Specifically, a Frag-Status attribute attributes for signaling. Specifically, a Frag-Status attribute
(7 octets) is included on every chunk of a packet, except the (7 bytes) is included in every chunk of a packet, except the last
last one. A RADIUS State attribute (from 3 to 255 octets) is one. A RADIUS State attribute (from 3 to 255 bytes) is also
also included in most chunks, to allow the RADIUS Server to bind included in most chunks, to allow the RADIUS Server to bind an
an Access-Request with a previous Access-Challenge. User-Name Access-Request with a previous Access-Challenge. User-Name
attributes (from 3 to 255 octets) are introduced on every chunk attributes (from 3 to 255 bytes) are included in every chunk the
the RADIUS Client sends as they are required by the proxies to RADIUS Client sends, as they are required by the proxies to route
route the packet to its destination. Together, these attributes the packet to its destination. Together, these attributes can
can generate from up to 13 to 517 octets of signalling data, generate from up to 13 to 517 bytes of signaling data, reducing
reducing the amount of payload information that can be sent on the amount of payload information that can be sent in each chunk.
each chunk.
3. RADIUS packets SHOULD be adjusted to avoid exceeding the network 3. RADIUS packets SHOULD be adjusted to avoid exceeding the network
MTU. Otherwise, IP fragmentation may occur, having undesirable MTU. Otherwise, IP fragmentation may occur, with undesirable
consequences. Hence, maximum chunk size would be decreased from consequences. Hence, maximum chunk size would be decreased from
4096 to the actual MTU of the network. 4096 to the actual MTU of the network.
4. The inclusion of Proxy-State attributes by intermediary proxies 4. The inclusion of Proxy-State attributes by intermediary proxies
can decrease the availability of usable space into the chunk. can decrease the availability of usable space in the chunk. This
This is described with further detail in Section 8.1. is described in further detail in Section 8.1.
7. Allowed large packet size 7. Allowed Large Packet Size
There are no provisions for signalling how much data is to be sent There are no provisions for signaling how much data is to be sent via
via the fragmentation process as a whole. It is difficult to define the fragmentation process as a whole. It is difficult to define what
what is meant by the "length" of any fragmented data. That data can is meant by the "length" of any fragmented data. That data can be
be multiple attributes, which includes RADIUS attribute header multiple attributes and can include RADIUS attribute header fields,
fields. Or it can be one or more "large" attributes (more than 256 or it can be one or more "large" attributes (more than 256 bytes in
octets in length). Proxies can also filter these attributes, to length). Proxies can also filter these attributes, to modify, add,
modify, add, or delete them and their contents. These proxies act on or delete them and their contents. These proxies act on a "packet by
a "packet by packet" basis, and cannot know what kind of filtering packet" basis and cannot know what kind of filtering actions they
actions they take on future packets. As a result, it is impossible will take on future packets. As a result, it is impossible to signal
to signal any meaningful value for the total amount of additional any meaningful value for the total amount of additional data.
data.
Unauthenticated end users are permitted to trigger the exchange of Unauthenticated end users are permitted to trigger the exchange of
large amounts of fragmented data between the RADIUS Client and the large amounts of fragmented data between the RADIUS Client and the
RADIUS Server, having the potential to allow Denial of Service (DoS) RADIUS Server, having the potential to allow denial-of-service (DoS)
attacks. An attacker could initiate a large number of connections, attacks. An attacker could initiate a large number of connections,
each of which requests the RADIUS Server to store a large amount of each of which requests the RADIUS Server to store a large amount of
data. This data could cause memory exhaustion on the RADIUS Server, data. This data could cause memory exhaustion on the RADIUS Server
and result in authentic users being denied access. It is worth and result in authentic users being denied access. It is worth
noting that authentication mechanisms are already designed to avoid noting that authentication mechanisms are already designed to avoid
exceeding the size limit. exceeding the size limit.
Hence, implementations of this specification MUST limit the total Hence, implementations of this specification MUST limit the total
amount of data they send and/or receive via this specification. Its amount of data they send and/or receive via this specification. Its
default value SHOULD be 100 kilo-octets. Any more than this may turn default value SHOULD be 100 kilobytes. Any more than this may turn
RADIUS into a generic transport protocol, which is undesired. This RADIUS into a generic transport protocol, which is undesirable. This
limit SHOULD be configurable, so that it can be changed if necessary. limit SHOULD be configurable, so that it can be changed if necessary.
Implementations of this specification MUST limit the total number of Implementations of this specification MUST limit the total number of
round trips used during the fragmentation process. Its default value round trips used during the fragmentation process. Its default value
SHOULD be to 25. Any more than this may indicate an implementation SHOULD be 25. Any more than this may indicate an implementation
error, misconfiguration, or a denial of service (DoS) attack. This error, misconfiguration, or DoS attack. This limit SHOULD be
limit SHOULD be configurable, so that it can be changed if necessary. configurable, so that it can be changed if necessary.
For instance, let's imagine the RADIUS Server wants to transport an For instance, let's imagine that the RADIUS Server wants to transport
SAML assertion which is 15000 octets long, to the RADIUS Client. In a SAML assertion that is 15000 bytes long to the RADIUS Client. In
this hypothetical scenario, we assume there are 3 intermediate this hypothetical scenario, we assume that there are three
proxies, each one inserting a Proxy-State attribute of 20 octets. intermediate proxies, each one inserting a Proxy-State attribute of
Also we assume the State attributes generated by the RADIUS Server 20 bytes. Also, we assume that the State attributes generated by the
have a size of 6 octets, and the User-Name attribute take 50 octets. RADIUS Server have a size of 6 bytes and the User-Name attribute
Therefore, the amount of free space in a chunk for the transport of takes 50 bytes. Therefore, the amount of free space in a chunk for
the SAML assertion attributes is: Total (4096) - RADIUS header (20) - the transport of the SAML assertion attributes is as follows:
User-Name (50 octets) - Frag-Status (7 octets) - Service-Type (6 Total (4096 bytes) - RADIUS header (20 bytes) - User-Name (50 bytes)
octets) - State (6 octets) - Proxy-State (20 octets) - Proxy-State - Frag-Status (7 bytes) - Service-Type (6 bytes) - State (6 bytes) -
(20) - Proxy-State (20) - Message-Authenticator (18 octets), Proxy-State (20 bytes) - Proxy-State (20 bytes) - Proxy-State
resulting in a total of 3929 octets, that is, 15 attributes of 255 (20 bytes) - Message-Authenticator (18 bytes), resulting in a total
bytes. of 3929 bytes. This amount of free space allows the transmission of
up to 15 attributes of 255 bytes each.
According to [RFC6929], a Long-Extended-Type provides a payload of According to [RFC6929], a Long-Extended-Type provides a payload of
251 octets. Therefore, the SAML assertion described above would 251 bytes. Therefore, the SAML assertion described above would
result into 60 attributes, requiring of 4 round-trips to be result in 60 attributes, requiring four round trips to be completely
completely transmitted. transmitted.
8. Handling special attributes 8. Handling Special Attributes
8.1. Proxy-State attribute 8.1. Proxy-State Attribute
RADIUS proxies may introduce Proxy-State attributes into any Access- RADIUS proxies may introduce Proxy-State attributes into any
Request packet they forward. If they are unable to add this Access-Request packet they forward. If they are unable to add this
information to the packet, they may silently discard forwarding it to information to the packet, they may silently discard it rather than
its destination, leading to DoS situations. Moreover, any Proxy- forward it to its destination; this would lead to DoS situations.
State attribute received by a RADIUS Server in an Access-Request Moreover, any Proxy-State attribute received by a RADIUS Server in an
packet MUST be copied into the reply packet to it. For these Access-Request packet MUST be copied into the corresponding reply
reasons, Proxy-State attributes require a special treatment within packet. For these reasons, Proxy-State attributes require special
the packet fragmentation mechanism. treatment within the packet fragmentation mechanism.
When the RADIUS Server replies to an Access-Request packet as part of When the RADIUS Server replies to an Access-Request packet as part of
a conversation involving a fragmentation (either a chunk or a request a conversation involving a fragmentation (either a chunk or a request
for chunks), it MUST include every Proxy-State attribute received for chunks), it MUST include every Proxy-State attribute received in
into the reply packet. This means that the RADIUS Server MUST take the reply packet. This means that the RADIUS Server MUST take into
into account the size of these Proxy-State attributes in order to account the size of these Proxy-State attributes in order to
calculate the size of the next chunk to be sent. calculate the size of the next chunk to be sent.
However, while a RADIUS Server will always know how much space MUST However, while a RADIUS Server will always know how much space MUST
be left on each reply packet for Proxy-State attributes (as they are be left in each reply packet for Proxy-State attributes (as they are
directly included by the RADIUS Server), a RADIUS Client cannot know directly included by the RADIUS Server), a RADIUS Client cannot know
this information, as Proxy-State attributes are removed from the this information, as Proxy-State attributes are removed from the
reply packet by their respective proxies before forwarding them back. reply packet by their respective proxies before forwarding them back.
Hence, RADIUS Clients need a mechanism to discover the amount of Hence, RADIUS Clients need a mechanism to discover the amount of
space required by proxies to introduce their Proxy-State attributes. space required by proxies to introduce their Proxy-State attributes.
In the following we describe a new mechanism to perform such a In the following paragraphs, we describe a new mechanism to perform
discovery: such a discovery:
1. When a RADIUS Client does not know how much space will be 1. When a RADIUS Client does not know how much space will be
required by intermediate proxies for including their Proxy-State required by intermediate proxies for including their Proxy-State
attributes, it SHOULD start using a conservative value (e.g. 1024 attributes, it SHOULD start using a conservative value (e.g.,
octets) as the chunk size. 1024 bytes) as the chunk size.
2. When the RADIUS Server receives a chunk from the RADIUS Client, 2. When the RADIUS Server receives a chunk from the RADIUS Client,
it can calculate the total size of the Proxy-State attributes it can calculate the total size of the Proxy-State attributes
that have been introduced by intermediary proxies along the path. that have been introduced by intermediary proxies along the path.
This information MUST be returned to the RADIUS Client in the This information MUST be returned to the RADIUS Client in the
next reply packet, encoded into a new attribute called Proxy- next reply packet, encoded into a new attribute called
State-Length. The RADIUS Server MAY artificially increase this Proxy-State-Length. The RADIUS Server MAY artificially increase
quantity in order to handle with situations where proxies behave this quantity in order to handle situations where proxies behave
inconsistently (e.g. they generate Proxy-State attributes with a inconsistently (e.g., they generate Proxy-State attributes with a
different size for each packet), or for situations where different size for each packet) or where intermediary proxies
intermediary proxies remove Proxy-State attributes generated by remove Proxy-State attributes generated by other proxies.
other proxies. Increasing this value would make the RADIUS Increasing this value would make the RADIUS Client leave some
Client to leave some free space for these situations. free space for these situations.
3. The RADIUS Client SHOULD react upon the reception of this 3. The RADIUS Client SHOULD respond to the reception of this
attribute by adjusting the maximum size for the next chunk attribute by adjusting the maximum size for the next chunk
accordingly. However, as the Proxy-State-Length offers just an accordingly. However, as the Proxy-State-Length offers just an
estimation of the space required by the proxies, the RADIUS estimation of the space required by the proxies, the RADIUS
Client MAY select a smaller amount in environments known to be Client MAY select a smaller amount in environments known to be
problematic. problematic.
8.2. State attribute 8.2. State Attribute
This RADIUS fragmentation mechanism makes use of the State attribute This RADIUS fragmentation mechanism makes use of the State attribute
to link all the chunks belonging to the same fragmented packet. to link all the chunks belonging to the same fragmented packet.
However, some considerations are required when the RADIUS Server is However, some considerations are required when the RADIUS Server is
fragmenting a packet that already contains a State attribute for fragmenting a packet that already contains a State attribute for
other purposes not related with the fragmentation. If the procedure other purposes not related to the fragmentation. If the procedure
described in Section 5 is followed, two different State attributes described in Section 5 is followed, two different State attributes
could be included into a single chunk, incurring into two problems. could be included in a single chunk. This is something explicitly
First, [RFC2865] explicitly forbids that more than one State forbidden in [RFC2865].
attribute appears into a single packet.
A straightforward solution consists on making the RADIUS Server to A straightforward solution consists of making the RADIUS Server send
send the original State attribute into the last chunk of the sequence the original State attribute in the last chunk of the sequence
(attributes can be re-ordered as specified in [RFC2865]). As the (attributes can be reordered as specified in [RFC2865]). As the last
last chunk (when generated by the RADIUS Server) does not contain any chunk (when generated by the RADIUS Server) does not contain any
State attribute due to the fragmentation mechanism, both situations State attribute due to the fragmentation mechanism, both situations
described above are avoided. described above are avoided.
Something similar happens when the RADIUS Client has to send a Something similar happens when the RADIUS Client has to send a
fragmented packet that contains a State attribute on it. The RADIUS fragmented packet that contains a State attribute in it. The RADIUS
Client MUST assure that this original State is included into the Client MUST ensure that this original State is included in the first
first chunk sent to the RADIUS Server (as this one never contains any chunk sent to the RADIUS Server (as this one never contains any State
State attribute due to fragmentation). attribute due to fragmentation).
8.3. Service-Type attribute 8.3. Service-Type Attribute
This RADIUS fragmentation mechanism makes use of the Service-Type This RADIUS fragmentation mechanism makes use of the Service-Type
attribute to indicate an Access-Accept packet is not granting access attribute to indicate that an Access-Accept packet is not granting
to the service yet, since additional authorization exchange needs to access to the service yet, since an additional authorization exchange
be performed. Similarly to the State attribute, the RADIUS Server needs to be performed. Similarly to the State attribute, the RADIUS
has to send the original Service-Type attribute into the last Access- Server has to send the original Service-Type attribute in the last
Accept of the RADIUS conversation to avoid ambiguity. Access-Accept of the RADIUS conversation to avoid ambiguity.
8.4. Rebuilding the original large packet 8.4. Rebuilding the Original Large Packet
The RADIUS Client stores the RADIUS attributes received on each chunk The RADIUS Client stores the RADIUS attributes received in each chunk
in order to be able to rebuild the original large packet after in a list, in order to be able to rebuild the original large packet
receiving the last chunk. However, some of these received attributes after receiving the last chunk. However, some of these received
MUST NOT be stored in this list, as they have been introduced as part attributes MUST NOT be stored in that list, as they have been
of the fragmentation signalling and hence, they are not part of the introduced as part of the fragmentation signaling and hence are not
original packet. part of the original packet.
o State (except the one in the last chunk, if present) o State (except the one in the last chunk, if present)
o Service-Type = Additional-Authorization o Service-Type = Additional-Authorization
o Frag-Status o Frag-Status
o Proxy-State-Length o Proxy-State-Length
Similarly, the RADIUS Server MUST NOT store the following attributes Similarly, the RADIUS Server MUST NOT store the following attributes
skipping to change at page 24, line 47 skipping to change at page 26, line 5
o State (except the one in the first chunk, if present) o State (except the one in the first chunk, if present)
o Service-Type = Additional-Authorization o Service-Type = Additional-Authorization
o Frag-Status o Frag-Status
o Proxy-State (except the ones in the last chunk) o Proxy-State (except the ones in the last chunk)
o User-Name (except the one in the first chunk) o User-Name (except the one in the first chunk)
9. New flag T field for the Long Extended Type attribute definition 9. New T Flag for the Long Extended Type Attribute Definition
This document defines a new field in the "Long Extended Type" This document defines a new field in the Long Extended Type attribute
attribute format. This field is one bit in size, and is called "T" format. This field is one bit in size and is called "T" for
for Truncation. It indicates that the attribute is intentionally Truncation. It indicates that the attribute is intentionally
truncated in this chunk, and is to be continued in the next chunk of truncated in this chunk and is to be continued in the next chunk of
the sequence. The combination of the flags "M" and "T" indicates the sequence. The combination of the M flag and the T flag indicates
that the attribute is fragmented (flag M), but that all the fragments that the attribute is fragmented (M flag) but that all the fragments
are not available in this chunk (flag T). Proxies implementing are not available in this chunk (T flag). Proxies implementing
[RFC6929] will see these attributes as invalid (they will not be able [RFC6929] will see these attributes as invalid (they will not be able
to reconstruct them), but they will still forward them as [RFC6929] to reconstruct them), but they will still forward them, as
section 5.2 indicates they SHOULD forward unknown attributes anyway. Section 5.2 of [RFC6929] indicates that they SHOULD forward unknown
attributes anyway.
As a consequence of this addition, the Reserved field is now 6 bits As a consequence of this addition, the Reserved field is now 6 bits
long (see Section 12.1 for some considerations). The following long (see Section 12.1 for some considerations). The following
figure represents the new attribute format. figure represents the new attribute format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Extended-Type |M|T| Reserved | | Type | Length | Extended-Type |M|T| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value ... | Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Updated Long Extended Type attribute format Figure 12: Updated Long Extended Type Attribute Format
10. New attribute definition 10. New Attribute Definition
This document proposes the definition of two new extended type This document proposes the definition of two new extended type
attributes, called Frag-Status and Proxy-State-Length. The format of attributes, called Frag-Status and Proxy-State-Length. The format of
these attributes follows the indications for an Extended Type these attributes follows the indications for an Extended Type
attribute defined in [RFC6929]. attribute defined in [RFC6929].
10.1. Frag-Status attribute 10.1. Frag-Status Attribute
This attribute is used for fragmentation signalling, and its meaning This attribute is used for fragmentation signaling, and its meaning
depends on the code value transported within it. The following depends on the code value transported within it. The following
figure represents the format of the Frag-Status attribute. figure represents the format of the Frag-Status attribute:
1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Extended-Type | Code | Type | Length | Extended-Type | Code
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code (cont) | Code (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Frag-Status format Figure 13: Frag-Status Format
Type Type
241 (To be confirmed by IANA)
241
Length Length
7 7
Extended-Type Extended-Type
TBD1 1
Code Code
4 byte. Integer indicating the code. The values defined in this 4 bytes. Integer indicating the code. The values defined in this
specifications are: specification are:
0 - Reserved 0 - Reserved
1 - Fragmentation-Supported 1 - Fragmentation-Supported
2 - More-Data-Pending 2 - More-Data-Pending
3 - More-Data-Request 3 - More-Data-Request
This attribute MAY be present in Access-Request, Access-Challenge and This attribute MAY be present in Access-Request, Access-Challenge,
Access-Accept packets. It MUST NOT be included in Access-Reject and Access-Accept packets. It MUST NOT be included in Access-Reject
packets. RADIUS Clients supporting this specification MUST include a packets. RADIUS Clients supporting this specification MUST include a
Frag-Status = Fragmentation-Supported attribute in the first Access- Frag-Status = Fragmentation-Supported attribute in the first
Request sent to the RADIUS Server, in order to indicate they would Access-Request sent to the RADIUS Server, in order to indicate that
accept fragmented data from the sever. they would accept fragmented data from the server.
10.2. Proxy-State-Length attribute 10.2. Proxy-State-Length Attribute
This attribute indicates to the RADIUS Client the length of the This attribute indicates to the RADIUS Client the length of the
Proxy-State attributes received by the RADIUS Server. This Proxy-State attributes received by the RADIUS Server. This
information is useful to adjust the length of the chunks sent by the information is useful for adjusting the length of the chunks sent by
RADIUS Client. The format of this Proxy-State-Length attribute is the RADIUS Client. The format of this Proxy-State-Length attribute
the following: is as follows:
1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Extended-Type | Value | Type | Length | Extended-Type | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value (cont) | Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Proxy-State-Length format Figure 14: Proxy-State-Length Format
Type Type
241 (To be confirmed by IANA) 241
Length Length
7 7
Extended-Type Extended-Type
TBD2 2
Value Value
4 octets. Total length (in octets) of received Proxy-State 4 bytes. Total length (in bytes) of received Proxy-State
attributes (including headers). As the RADIUS "length" field attributes (including headers). As the RADIUS Length field cannot
cannot take values over 4096 octets, values of Proxy-State-Length take values over 4096 bytes, values of Proxy-State-Length MUST be
MUST be less than that maximum length. less than that maximum length.
This attribute MAY be present in Access-Challenge and Access-Accept This attribute MAY be present in Access-Challenge and Access-Accept
packets. It MUST NOT be included in Access-Request or Access-Reject packets. It MUST NOT be included in Access-Request or Access-Reject
packets. packets.
10.3. Table of attributes 10.3. Table of Attributes
The following table shows the different attributes defined in this The following table shows the different attributes defined in this
document related with the kind of RADIUS packets where they can be document, along with the types of RADIUS packets in which they can be
present. present.
| Kind of packet | | Type of Packet |
+-----+-----+-----+-----+ +-----+-----+-----+-----+
Attribute Name | Req | Acc | Rej | Cha | Attribute Name | Req | Acc | Rej | Cha |
----------------------+-----+-----+-----+-----+ ----------------------+-----+-----+-----+-----+
Frag-Status | 0-1 | 0-1 | 0 | 0-1 | Frag-Status | 0-1 | 0-1 | 0 | 0-1 |
----------------------+-----+-----+-----+-----+ ----------------------+-----+-----+-----+-----+
Proxy-State-Length | 0 | 0-1 | 0 | 0-1 | Proxy-State-Length | 0 | 0-1 | 0 | 0-1 |
----------------------+-----+-----+-----+-----+ ----------------------+-----+-----+-----+-----+
11. Operation with proxies 11. Operation with Proxies
The fragmentation mechanism defined above is designed to be The fragmentation mechanism defined above is designed to be
transparent to legacy proxies, as long as they do not want to modify transparent to legacy proxies, as long as they do not want to modify
any fragmented attribute. Nevertheless, updated proxies supporting any fragmented attribute. Nevertheless, updated proxies supporting
this specification can even modify fragmented attributes. this specification can even modify fragmented attributes.
11.1. Legacy proxies 11.1. Legacy Proxies
As every chunk is indeed a RADIUS packet, legacy proxies treat them As every chunk is indeed a RADIUS packet, legacy proxies treat them
as the rest of packets, routing them to their destination. Proxies as they would the rest of the packets, routing them to their
can introduce Proxy-State attributes to Access-Request packets, even destination. Proxies can introduce Proxy-State attributes into
if they are indeed chunks. This will not affect how fragmentation is Access-Request packets, even if they are indeed chunks. This will
managed. The RADIUS Server will include all the received Proxy-State not affect how fragmentation is managed. The RADIUS Server will
attributes into the generated response, as described in [RFC2865]. include all the received Proxy-State attributes in the generated
Hence, proxies do not distinguish between a regular RADIUS packet and response, as described in [RFC2865]. Hence, proxies do not
a chunk. distinguish between a regular RADIUS packet and a chunk.
11.2. Updated proxies 11.2. Updated Proxies
Updated proxies can interact with RADIUS Clients and Servers in order Updated proxies can interact with RADIUS Clients and Servers in order
to obtain the complete large packet before starting forwarding it. to obtain the complete large packet before starting to forward it.
In this way, proxies can manipulate (modify and/or remove) any In this way, proxies can manipulate (modify and/or remove) any
attribute of the packet, or introduce new attributes, without attribute of the packet or introduce new attributes, without worrying
worrying about crossing the boundaries of the chunk size. Once the about crossing the boundaries of the chunk size. Once the
manipulated packet is ready, it is sent to the original destination manipulated packet is ready, it is sent to the original destination
using the fragmentation mechanism (if required). The following using the fragmentation mechanism (if required). The example in
example shows how an updated proxy interacts with the RADIUS Client Figure 15 shows how an updated proxy interacts with the RADIUS Client
to obtain a large Access-Request packet, modify an attribute to (1) obtain a large Access-Request packet and (2) modify an
resulting into an even more large packet, and interacts with the attribute, resulting in an even larger packet. The proxy then
RADIUS Server to complete the transmission of the modified packet. interacts with the RADIUS Server to complete the transmission of the
modified packet, as shown in Figure 16.
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| RADIUS | | RADIUS | | RADIUS | | RADIUS |
| Client | | Proxy | | Client | | Proxy |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| | | |
| Access-Request(1){User-Name,Calling-Station-Id, | | Access-Request(1){User-Name,Calling-Station-Id, |
| Example-Long-1[M],Example-Long-1[M], | | Example-Long-1[M],Example-Long-1[M], |
| Example-Long-1[M],Example-Long-1[M], | | Example-Long-1[M],Example-Long-1[M], |
| Example-Long-1[MT],Frag-Status(MDP)} | | Example-Long-1[MT],Frag-Status(MDP)} |
|--------------------------------------------------->| |--------------------------------------------------->|
| | | |
| Access-Challenge(1){User-Name, | | Access-Challenge(1){User-Name, |
| Frag-Status(MDR),State1} | | Frag-Status(MDR),State1} |
|<---------------------------------------------------| |<---------------------------------------------------|
| | | |
| Access-Request(2)(User-Name,State1, | | Access-Request(2){User-Name,State1, |
| Example-Long-1[M],Example-Long-1[M], | | Example-Long-1[M],Example-Long-1[M], |
| Example-Long-1[M],Example-Long-1} | | Example-Long-1[M],Example-Long-1} |
|--------------------------------------------------->| |--------------------------------------------------->|
PROXY MODIFIES ATTRIBUTE Data INCREASING ITS Proxy Modifies Attribute Data, Increasing Its
SIZE FROM 9 FRAGMENTS TO 11 FRAGMENTS Size from 9 Fragments to 11 Fragments
Figure 15: Updated proxy interacts with RADIUS Client Figure 15: Updated Proxy Interacts with RADIUS Client
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| RADIUS | | RADIUS | | RADIUS | | RADIUS |
| Proxy | | Server | | Proxy | | Server |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| | | |
| Access-Request(3){User-Name,Calling-Station-Id, | | Access-Request(3){User-Name,Calling-Station-Id, |
| Example-Long-1[M],Example-Long-1[M], | | Example-Long-1[M],Example-Long-1[M], |
| Example-Long-1[M],Example-Long-1[M], | | Example-Long-1[M],Example-Long-1[M], |
| Example-Long-1[MT],Frag-Status(MDP)} | | Example-Long-1[MT],Frag-Status(MDP)} |
|--------------------------------------------------->| |--------------------------------------------------->|
| | | |
| Access-Challenge(1){User-Name, | | Access-Challenge(1){User-Name, |
| Frag-Status(MDR),State2} | | Frag-Status(MDR),State2} |
skipping to change at page 30, line 33 skipping to change at page 31, line 33
| Example-Long-1[MT],Frag-Status(MDP)} | | Example-Long-1[MT],Frag-Status(MDP)} |
|--------------------------------------------------->| |--------------------------------------------------->|
| | | |
| Access-Challenge(1){User-Name, | | Access-Challenge(1){User-Name, |
| Frag-Status(MDR),State3} | | Frag-Status(MDR),State3} |
|<---------------------------------------------------| |<---------------------------------------------------|
| | | |
| Access-Request(5){User-Name,State3,Example-Long-1} | | Access-Request(5){User-Name,State3,Example-Long-1} |
|--------------------------------------------------->| |--------------------------------------------------->|
Figure 16: Updated proxy interacts with RADIUS Server Figure 16: Updated Proxy Interacts with RADIUS Server
12. General considerations 12. General Considerations
12.1. Flag T 12.1. T Flag
As described in Section 9, this document modifies the definition of As described in Section 9, this document modifies the definition of
the "Reserved" field of the "Long Extended Type" attribute [RFC6929], the Reserved field of the Long Extended Type attribute [RFC6929] by
by allocating an additional flag "T". The meaning and position of allocating an additional flag called the T flag. The meaning and
this flag is defined in this document, and nowhere else. This might position of this flag are defined in this document, and nowhere else.
generate an issue if subsequent specifications want to allocate a new This might cause an issue if subsequent specifications want to
flag as well, as there would be no direct way for them to know which allocate a new flag as well, as there would be no direct way for them
parts of the "Reserved" field have already been defined. to know which parts of the Reserved field have already been defined.
An immediate and reasonable solution for this issue would be An immediate and reasonable solution for this issue would be
declaring that this RFC updates [RFC6929]. In this way, [RFC6929] declaring that this RFC updates [RFC6929]. In this way, [RFC6929]
would include an "Updated by" clause that will point readers to this would include an "Updated by" clause that will point readers to this
document. Another alternative would be creating an IANA registry for document. Another alternative would be creating an IANA registry for
the "Reserved" field. However, the working group thinks that would the Reserved field. However, the RADIUS Extensions (RADEXT) working
be overkill, as not such a great number of specifications extending group thinks that would be overkill, as a large number of
that field are expected. specifications extending that field are not expected.
In the end, the proposed solution is that this experimental RFC In the end, the proposed solution is that this experimental RFC
should not update RFC 6929. Instead, we rely on the collective mind should not update RFC 6929. Instead, we rely on the collective mind
of the WG to recall that this T flag is used. When/if the experiment of the working group to remember that this T flag is being used as
will be successful, the T flag will be properly assigned. specified by this Experimental document. If the experiment is
successful, the T flag will be properly assigned.
12.2. Violation of RFC2865 12.2. Violation of RFC 2865
Section 5.1 indicates that all authorization and authentication Section 5.1 indicates that all authorization and authentication
handling will be postponed until all the chunks have been received. handling will be postponed until all the chunks have been received.
This postponement also affects to the verification that the Access- This postponement also applies to the verification that the
Request packet contains some kind of authentication attribute (e.g. Access-Request packet contains some kind of authentication attribute
User-Password, CHAP-Password, State or other future attribute), as (e.g., User-Password, CHAP-Password, State, or other future
required by [RFC2865]. This checking will therefore be delayed until attribute), as required by [RFC2865]. This checking will therefore
the original large packet has been rebuilt, as some of the chunks may be delayed until the original large packet has been rebuilt, as some
not contain any of them. of the chunks may not contain any of them.
The authors acknowledge that this specification violates the "MUST" The authors acknowledge that this specification violates the "MUST"
requirement of [RFC2865] Section 4.1 that states that "An Access- requirement of [RFC2865], Section 4.1 that states that "An
Request MUST contain either a User-Password or a CHAP- Password or a Access-Request MUST contain either a User-Password or a CHAP-Password
State". We note that a proxy which enforces that requirement would or a State." We note that a proxy that enforces that requirement
be unable to support future RADIUS authentication extensions. would be unable to support future RADIUS authentication extensions.
Extensions to the protocol would therefore be impossible to deploy. Extensions to the protocol would therefore be impossible to deploy.
All known implementations have chosen the philosophy of "be liberal All known implementations have chosen the philosophy of "be liberal
in what you accept". That is, they accept traffic which violates the in what you accept." That is, they accept traffic that violates the
requirement of [RFC2865] Section 4.1. We therefore expect to see no requirement of [RFC2865], Section 4.1. We therefore expect to see no
operational issues with this specification. After we gain more operational issues with this specification. After we gain more
operational experience with this specification, it can be re-issued operational experience with this specification, it can be reissued as
as a standards track document, and update [RFC2865]. a Standards Track document and can update [RFC2865].
12.3. Proxying based on User-Name 12.3. Proxying Based on User-Name
This proposal assumes legacy proxies to base their routing decisions This proposal assumes that legacy proxies base their routing
on the value of the User-Name attribute. For this reason, every decisions on the value of the User-Name attribute. For this reason,
packet sent from the RADIUS Client to the RADIUS Server (either every packet sent from the RADIUS Client to the RADIUS Server (either
chunks or requests for more chunks) MUST contain a User-Name chunks or requests for more chunks) MUST contain a User-Name
attribute. attribute.
12.4. Transport behaviour 12.4. Transport Behavior
This proposal does not modify the way RADIUS interacts with the This proposal does not modify the way RADIUS interacts with the
underlying transport (UDP). That is, RADIUS keeps following a lock- underlying transport (UDP). That is, RADIUS keeps following a
step behaviour, that requires receiving an explicit acknowledge for lock-step behavior that requires receiving an explicit
each chunk sent. Hence, bursts of traffic which could congest links acknowledgement for each chunk sent. Hence, bursts of traffic
between peers are not an issue. that could congest links between peers are not an issue.
Another benefit of the lock-step nature of RADIUS, is that there are Another benefit of the lock-step nature of RADIUS is that there are
no security issues with overlapping fragments. Each chunk simply has no security issues with overlapping fragments. Each chunk simply has
a length, with no "fragment offset" field as with IPv4. The order of a length, with no Fragment Offset field as with IPv4. The order of
the fragments is determined by the order in which they are received. the fragments is determined by the order in which they are received.
There is no ambiguity about the size or placement of each chunk, and There is no ambiguity about the size or placement of each chunk, and
therefore no security issues associated with overlapping chunks. therefore no security issues associated with overlapping chunks.
13. Security Considerations 13. Security Considerations
As noted in many earlier specifications ([RFC5080], [RFC6158], etc.) As noted in many earlier specifications ([RFC5080], [RFC6158], etc.),
RADIUS security is problematic. This specification changes nothing RADIUS security is problematic. This specification changes nothing
related to the security of the RADIUS protocol. It requires that all related to the security of the RADIUS protocol. It requires that all
Access-Request packets associated with fragmentation are Access-Request packets associated with fragmentation are
authenticated using the existing Message-Authenticator attribute. authenticated using the existing Message-Authenticator attribute.
This signature prevents forging and replay, to the limits of the This signature prevents forging and replay, to the limits of the
existing security. existing security.
The ability to send bulk data from one party to another creates new The ability to send bulk data from one party to another creates new
security considerations. RADIUS Clients and Servers may have to security considerations. RADIUS Clients and Servers may have to
store large amounts of data per session. The amount of this data can store large amounts of data per session. The amount of this data can
be significant, leading to the potential for resource exhaustion. We be significant, leading to the potential for resource exhaustion. We
therefore suggest that implementations limit the amount of bulk data therefore suggest that implementations limit the amount of bulk data
stored per session. The exact method for this limitation is stored per session. The exact method for this limitation is
implementation-specific. Section 7 gives some indications on what implementation-specific. Section 7 gives some indications of what
could be reasonable limits. could be reasonable limits.
The bulk data can often be pushed off to storage methods other than The bulk data can often be pushed off to storage methods other than
the memory of the RADIUS implementation. For example, it can be the memory of the RADIUS implementation. For example, it can be
stored in an external database, or in files. This approach mitigates stored in an external database or in files. This approach mitigates
the resource exhaustion issue, as RADIUS Servers today already store the resource exhaustion issue, as RADIUS Servers today already store
large amounts of accounting data. large amounts of accounting data.
14. IANA Considerations 14. IANA Considerations
The authors request that Attribute Types and Attribute Values defined The Internet Assigned Numbers Authority (IANA) has registered the
in this document be registered by the Internet Assigned Numbers Attribute Types and Attribute Values defined in this document in the
Authority (IANA) from the RADIUS namespaces as described in the "IANA RADIUS namespaces as described in the "IANA Considerations" section
Considerations" section of [RFC3575], in accordance with BCP 26 of [RFC3575], in accordance with BCP 26 [RFC5226]. For RADIUS
[RFC5226]. For RADIUS packets, attributes and registries created by packets, attributes, and registries created by this document, IANA
this document IANA is requested to place them at has updated <http://www.iana.org/assignments/radius-types>
http://www.iana.org/assignments/radius-types. accordingly.
In particular, this document defines two new RADIUS attributes, In particular, this document defines two new RADIUS attributes,
entitled "Frag-Status" and "Proxy-State-Length" (see Section 10), entitled "Frag-Status" (value 241.1) and "Proxy-State-Length"
with assigned values of 241.TBD1 and 241.TBD2 from the Short Extended (value 241.2), which have been allocated from the short extended
Space of [RFC6929]: space as described in [RFC6929]:
Type Name Length Meaning Type Name Length Meaning
---- ---- ------ ------- ---- ---- ------ -------
241.TBD1 Frag-Status 7 Signals fragmentation 241.1 Frag-Status 7 Signals fragmentation
241.TBD2 Proxy-State-Length 7 Indicates the length of the 241.2 Proxy-State-Length 7 Indicates the length of the
received Proxy-State attributes received Proxy-State attributes
The Frag-Status attribute also defines a 8-bit "Code" field, for The Frag-Status attribute also defines an 8-bit "Code" field, for
which the IANA is to create and maintain a new sub-registry entitled which IANA has created and now maintains a new sub-registry entitled
"Code values" under the RADIUS "Frag-Status" attribute. Initial "Code Values for RADIUS Attribute 241.1, Frag-Status". Initial
values for the RADIUS Frag-Status "Code" registry are given below; values for the RADIUS Frag-Status "Code" registry are given below;
future assignments are to be made through "RFC required" [RFC5226]. future assignments are to be made through "RFC Required" [RFC5226].
Assignments consist of a Frag-Status "Code" name and its associated Assignments consist of a Frag-Status "Code" name and its associated
value. value.
Value Frag-Status Code Name Definition Value Frag-Status Code Name Definition
---- ------------------------ ---------- ---- ------------------------ ----------
0 Reserved See Section 10.1 0 Reserved See Section 10.1
1 Fragmentation-Supported See Section 10.1 1 Fragmentation-Supported See Section 10.1
2 More-Data-Pending See Section 10.1 2 More-Data-Pending See Section 10.1
3 More-Data-Request See Section 10.1 3 More-Data-Request See Section 10.1
4-255 Unassigned 4-255 Unassigned
Additionally, allocation of a new Service-Type value for "Additional- Additionally, IANA has allocated a new Service-Type value for
Authorization" is requested. "Additional-Authorization".
Value Service Type Value Definition
---- ------------------------ ----------
TBA Additional-Authorization See Section 5.1
15. Acknowledgements
The authors would like to thank the members of the RADEXT working
group who have contributed to the development of this specification,
either by participating on the discussions on the mailing lists or by
sending comments about our RFC.
The authors also thank David Cuenca (University of Murcia) for Value Service Type Value Definition
implementing a proof of concept implementation of this RFC that has ---- ------------------------ ----------
been useful to improve the quality of the specification. 19 Additional-Authorization See Section 5.1
This work has been partly funded by the GEANT GN3+ SA5 and CLASSe 15. References
(http://sec.cs.kent.ac.uk/CLASSe/) projects.
16. References 15.1. Normative References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", "Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000. RFC 2865, June 2000, <http://www.rfc-editor.org/
info/rfc2865>.
[RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote
Authentication Dial In User Service)", RFC 3575, Authentication Dial In User Service)", RFC 3575,
July 2003. July 2003, <http://www.rfc-editor.org/info/rfc3575>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008, <http://www.rfc-editor.org/info/rfc5226>.
[RFC6158] DeKok, A. and G. Weber, "RADIUS Design Guidelines", [RFC6158] DeKok, A., Ed., and G. Weber, "RADIUS Design Guidelines",
BCP 158, RFC 6158, March 2011. BCP 158, RFC 6158, March 2011,
<http://www.rfc-editor.org/info/rfc6158>.
[RFC6929] DeKok, A. and A. Lior, "Remote Authentication Dial In User [RFC6929] DeKok, A. and A. Lior, "Remote Authentication Dial In User
Service (RADIUS) Protocol Extensions", RFC 6929, Service (RADIUS) Protocol Extensions", RFC 6929,
April 2013. April 2013, <http://www.rfc-editor.org/info/rfc6929>.
16.2. Informative References
[I-D.ietf-abfab-aaa-saml] 15.2. Informative References
Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding,
Profiles, Name Identifier Format, and Confirmation Methods
for SAML", draft-ietf-abfab-aaa-saml-09 (work in
progress), February 2014.
[I-D.ietf-abfab-arch] [ABFAB-Arch]
Howlett, J., Hartman, S., Tschofenig, H., Lear, E., and J. Howlett, J., Hartman, S., Tschofenig, H., Lear, E., and J.
Schaad, "Application Bridging for Federated Access Beyond Schaad, "Application Bridging for Federated Access Beyond
Web (ABFAB) Architecture", draft-ietf-abfab-arch-13 (work Web (ABFAB) Architecture", Work in Progress,
in progress), July 2014. draft-ietf-abfab-arch-13, July 2014.
[I-D.ietf-radext-bigger-packets] [RADIUS-Larger-Pkts]
Hartman, S., "Larger Packets for RADIUS over TCP", Hartman, S., "Larger Packets for RADIUS over TCP", Work in
draft-ietf-radext-bigger-packets-01 (work in progress), Progress, draft-ietf-radext-bigger-packets-03, March 2015.
July 2014.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000,
<http://www.rfc-editor.org/info/rfc2866>.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003. Authentication Protocol (EAP)", RFC 3579, September 2003,
<http://www.rfc-editor.org/info/rfc3579>.
[RFC4849] Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Filter [RFC4849] Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Filter
Rule Attribute", RFC 4849, April 2007. Rule Attribute", RFC 4849, April 2007,
<http://www.rfc-editor.org/info/rfc4849>.
[RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication [RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication
Dial In User Service (RADIUS) Implementation Issues and Dial In User Service (RADIUS) Implementation Issues and
Suggested Fixes", RFC 5080, December 2007. Suggested Fixes", RFC 5080, December 2007,
<http://www.rfc-editor.org/info/rfc5080>.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. [RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176, Authentication Dial In User Service (RADIUS)", RFC 5176,
January 2008. January 2008, <http://www.rfc-editor.org/info/rfc5176>.
[SAML-RADIUS]
Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A
RADIUS Attribute, Binding, Profiles, Name Identifier
Format, and Confirmation Methods for SAML", Work in
Progress, draft-ietf-abfab-aaa-saml-10, February 2015.
Acknowledgements
The authors would like to thank the members of the RADEXT working
group who have contributed to the development of this specification
by either participating in the discussions on the mailing lists or
sending comments about our RFC.
The authors also thank David Cuenca (University of Murcia) for
implementing a proof-of-concept implementation of this RFC that has
been useful to improve the quality of the specification.
This work has been partly funded by the GEANT GN3+ SA5 and CLASSe
(<http://www.um.es/classe/>) projects.
Authors' Addresses Authors' Addresses
Alejandro Perez-Mendez (Ed.) Alejandro Perez-Mendez (editor)
University of Murcia University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100 Murcia 30100
Spain Spain
Phone: +34 868 88 46 44 Phone: +34 868 88 46 44
Email: alex@um.es EMail: alex@um.es
Rafa Marin-Lopez Rafa Marin-Lopez
University of Murcia University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100 Murcia 30100
Spain Spain
Phone: +34 868 88 85 01 Phone: +34 868 88 85 01
Email: rafa@um.es EMail: rafa@um.es
Fernando Pereniguez-Garcia Fernando Pereniguez-Garcia
University of Murcia University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100 Murcia 30100
Spain Spain
Phone: +34 868 88 78 82 Phone: +34 868 88 78 82
Email: pereniguez@um.es EMail: pereniguez@um.es
Gabriel Lopez-Millan Gabriel Lopez-Millan
University of Murcia University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100 Murcia 30100
Spain Spain
Phone: +34 868 88 85 04 Phone: +34 868 88 85 04
Email: gabilm@um.es EMail: gabilm@um.es
Diego R. Lopez Diego R. Lopez
Telefonica I+D Telefonica I+D
Don Ramon de la Cruz, 84 Don Ramon de la Cruz, 84
Madrid, 28006 Madrid 28006
Spain Spain
Phone: +34 913 129 041 Phone: +34 913 129 041
Email: diego@tid.es EMail: diego@tid.es
Alan DeKok Alan DeKok
Network RADIUS Network RADIUS SARL
15 av du Granier 57bis Boulevard des Alpes
Meylan, 38240 Meylan 38240
France France
Phone: +34 913 129 041 EMail: aland@networkradius.com
Email: aland@networkradius.com
URI: http://networkradius.com URI: http://networkradius.com
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