RADIUS EXTensions Working Group A. Perez-Mendez
Internet-Draft R. Marin-Lopez
Intended status: Experimental F. Pereniguez-Garcia
Expires: August 4, 2012 G. Lopez-Millan
University of Murcia
D. Lopez
Telefonica I+D
A. DeKok
Network RADIUS
Feb 2012
Support of fragmentation of RADIUS packets
draft-perez-radext-radius-fragmentation-01
Abstract
This document describes a mechanism providing fragmentation support
of RADIUS packets that exceed the 4 KB limit.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 4, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. More-Data-Pending attribute . . . . . . . . . . . . . . . . . 4
4. Fragmentation of Access-Request packets . . . . . . . . . . . 5
5. Fragmentation of Access-Challenge packets . . . . . . . . . . 7
6. Fragmentation of Access-Accept packets . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
RADIUS [RFC2865] is a protocol for carrying authentication,
authorization, and configuration information between a Network Access
Server (NAS) which desires to authenticate its links and a shared
Authentication Server (AS). Information is exchanged between the NAS
and the AS through packets. Each RADIUS packet can transport several
RADIUS attributes, to convey the necessary information to the other
peer, up to a maximum size of 4 KB of total data (including RADIUS
packet headers). RADIUS attributes have a maximum size of 253 bytes
of payload.
RADIUS has been extensively used along the years. Along this time,
the need of sending RADIUS attributes larger than 253 bytes has
become a reality. An immediate alternative to overcome this issue
consists in splitting the data into a group of RADIUS attributes of
the same type, and then insert them into the RADIUS packet in order.
At the destination, the content of these attributes is extracted and
joined to rebuild the original data. This scheme is followed, for
example, by RADIUS-EAP [RFC3579]. A more advanced solution is given
in [I-D.ietf-radext-radius-extensions], where extended attributes can
be marked with a flag to indicate fragmentation. A reference-based
mechanism is also proposed in [RFC6158], where attribute can be
obtained through an out-of-band protocol.
However, there are no proposals to deal with fragmentation at a
packet level, when the total length exceeds the 4 KB limit imposed by
the RADIUS specification. As the usage of RADIUS is being considered
in more complex AAA scenarios, including the exchange of richer data,
like SAML assertions or JWT tokens, exceeding this limit becomes more
likely, thus making necessary the availability of mechanisms for
dealing with this situation.
This document defines a mechanism to allow RADIUS peers to exchange
packets that exceed the 4 KB limit, by fragmenting them across
several exchanges. This proposal tries to maintain compatibility
with any intra-packet fragmentation mechanism and with the existing
RADIUS deployments.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Overview
When a RADIUS peer needs to send a packet that exceeds the 4 KB, the
following mechanism is used. First, the large packet is split into
several smaller RADIUS packets (i.e. chunks) of the same type (e.g.
Access-Request). The first chunk contains the first "n" RADIUS
attributes of the original packet (in the same order), until a limit
of 4092 bytes (4096 - 4) is reached. It can be less, depending on
the specific length of the attributes, but never more. If there are
still attributes from the original packet that have not been yet
included into any chunk, a new attribute called More-Data-Pending is
appended into the chunk. This process is repeated until all the
RADIUS attributes from the original packet have been included into
some chunk.
Then the first chunk is sent to the peer, which identifies the packet
as a chunk (the More-Data-Pending attribute is present), and requests
for the rest of the chunks. Once all the chunks have been received
by the peer, the original packet is reconstructed and processed as if
it had been received in one piece.
When a packet is truncated into chunks, a special situation may occur
in combination with Extended Type attributes as defined in
[I-D.ietf-radext-radius-extensions]. If the truncation occurs in the
middle of a fragmented attribute, the last attribute of the chunk
will be an Extended Type with Flags, with flag M enabled. This
situation is specifically forbidden in
[I-D.ietf-radext-radius-extensions]. To indicate that this situation
is provoked by a truncation and hence MUST be allowed, a new flag "T"
(indicating truncation) MUST be set into that Extended-Type-Flag
attribute. The combination of the flags "M" and "T" indicates that
the attribute is fragmented (flag M), but that all the fragments are
not available in this chunk (flag T).
Indeed, this situation will be the most usual. When packet
fragmentation is required, usually it will be motivated by the
inclusion of one or more large attribute that makes use of attribute
fragmentation. Hence, the truncation will probably split the large
attribute into two (or more) pieces. The rest of possibilities,
where the truncation point does not split a fragmented attribute,
does not require any special treatment.
3. More-Data-Pending attribute
This document proposes the definition of a new extended type
attribute, called More-Data-Pending. The format of this attribute
follows the indications of an Extended Type attribute defined in
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[I-D.ietf-radext-radius-extensions]. The presence of this attribute
indicates that the received RADIUS packet is not complete (i.e. it is
a chunk), and more data MUST be received to regenerate the original
packet. The following figure represents the format of the More-Data-
Pending attribute.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Extended-Type | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: More-Data-Pending format
Type
To be assigned (TBA)
Length
4
Extended-Type
To be assigned (TBA).
Value
1 byte. Not defined yet.
This attribute MAY be present in Access-Request and Acess-Challenge
packets. It MUST not be included in Acess-Accept packets.
4. Fragmentation of Access-Request packets
When the NAS desires to send a RADIUS packet that exceeds the 4 KB
limit, the packet can be split into smaller packets (chunks) and sent
over different exchanges. This fact is indicated by including a
More-Data-Pending attribute on each chunk (except the last one of the
series). The process is described in detail using the following
example. In this example, the attributes "Data" and "Other" are
Extended Type with Flags, as defined in
[I-D.ietf-radext-radius-extensions].
In order to make the example simpler, it is assumed that each RADIUS
packet can include up to 8 RADIUS attributes, instead of using bytes.
Flag M is indicated as [M]. Flag T is indicated as [T]. Presence of
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both is indicated as [MT]. Data1, Data2, Data3... indicate
successive fragments of the attribute "Data".
o The RADIUS client wants to send the following RADIUS packet:
Access-Request = User-Name, Calling-Station-Id, Data1[M],
Data2[M], Data3[M], Data4[M], Data5[M], Data6[M], Data7[M],
Data8[M], Data9[M], Data10, Other1[M], Other2[M], Other3
o As the RADIUS packet exceeds the maximum allowed length (8
attributes), the RADIUS client truncates the packet to generate
the first chunk, including the More-Data-Pending attribute. Flag
"T" is activated into the fragment "Data5", as it is the last of
the packet (chunk), but not the last of the fragmented attribute.
Access-Request-1 = User-Name, Calling-Station-Id, Data1[M],
Data2[M], Data3[M], Data4[M], Data5[MT], More-Data-Pending
o When the server receives the RADIUS packet containing the More-
Data-Pending attribute, the processing of the packet is delayed
until all the pending data is received. The pending data is
requested by means of an Access-Challenge packet, using the State
attribute to tie together this response with the subsequent
request from the client.
Access-Challenge-1 = State1
o The client continues including attributes until another RADIUS
packet (i.e. chunk) is completed, appending again the More-Data-
Pending attribute. The State attribute received in the Access-
Challenge is also included in this chunk. Again, flag "T" is
enabled in the last fragment of the chunk to indicate that a
truncation took place.
Acess-Request-2 = State1, Data6[M], Data7[M], Data8[M],
Data9[M], Data10, Other1[MT], More-Data-Pending
o As the received request contains the More-Data-Pending, the server
stores the attributes into the state associated to State1 and
replies with another Access-Challenge. The challenge contains a
new State attribute that refers to this conversation.
Access-Challenge-2 = State2
o Finally, the client sends the last chunk of the original packet,
including the received State attribute.
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Access-Request-3 = State2, Other2[M], Other3
o On reception of this last chunk (no More-Data-Pending attribute
present), the server can process the totality of the received
attributes as if they all had been received into a single RADIUS
packet larger than 4 KB.
The following figure depicts the exchange of chucks between the NAS
and the AS.
+-+-+-+-+ +-+-+-+-+
| NAS | | AS |
+-+-+-+-+ +-+-+-+-+
| |
| Access-Request(User-Name,Calling-Station-Id, |
| Data1[M],Data2[M],Data3[M],Data4[M], |
| Data5[MT],More-Data-Pending) |
|-------------------------------------------------------->|
| |
| Access-Challenge(State1) |
|<--------------------------------------------------------|
| |
| Access-Request(State1,Data6[M],Data7[M],Data8[M], |
| Data9[M],Data10,Other1[MT], |
| More-Data-Pending |
|-------------------------------------------------------->|
| |
| Access-Challenge(State2) |
|<--------------------------------------------------------|
| |
| Access-Request(State2,Other2[M],Other3) |
|-------------------------------------------------------->|
Figure 2: Fragmented Access-Request packet
5. Fragmentation of Access-Challenge packets
When is the server (AS) the one who wants to send a large RADIUS
packet, the solution is very similar to the previous one. The one
difference is that in this scenario, the AS includes a State
attribute along with the More-Data-Required.
The following figure depicts how the message exchange would be if the
AS wanted to send a large packet to the NAS. Specifically, it wants
to send the following challenge:
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Access-Challenge = Data1[M], Data2[M], Data3[M], Data4[M],
Data5[M], Data6[M], Data7[M], Data8[M], Data9[M], Data10,
Other1[M], Other2[M], Other3
+-+-+-+-+ +-+-+-+-+
| NAS | | AS |
+-+-+-+-+ +-+-+-+-+
| |
| Access-Challenge(Data1[M],Data2[M],Data3[M], |
| Data4[M],Data5[M],Data6[MT], |
| More-Data-Pending,State1) |
|<--------------------------------------------------------|
| |
| Access-Request(State1) |
|-------------------------------------------------------->|
| |
| Access-Challenge(Data7[M],Data8[M],Data9[M], |
| Data10,Other1[M],Other2[MT], |
| More-Data-Pending,State2) |
|<--------------------------------------------------------|
| |
| Access-Request(State2) |
|-------------------------------------------------------->|
| |
| Access-Challenge(Other3) |
|<--------------------------------------------------------|
Figure 3: Fragmented Access-Challenge packet
6. Fragmentation of Access-Accept packets
If the AS wants to send an Access-Accept packet that exceeds the 4 KB
limit, the operation is slightly different. As some attributes are
allowed to appear in Access-Accept packets, but not in Access-
Challenge packets, the solution described in the previous sections is
not directly applicable. Instead, the AS MUST send an Access-Accept
packet to the NAS containing all the attributes that can not be
included in Access-Challenge packets, and indicating "Authorize-Only"
as the Service-Type. The additional attributes are received via a
series of Access-Request/Access-Challenge exchanges, as described in
the previous section. Finally, the last packet from the AS to the
NAS would be an Access-Accept containing the real Service-Type for
the user. For simpliciy, Service-Type[X] indicates a Service-Type
attribute of value X.
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o The AS wants to send the following Access-Accept packet:
Access-Accept = User-Name, Service-Type[X], Framed-IP-Address,
Data1[M], Data2[M], Data3[M], Data4[M], Data5[M], Data6[M],
Data7[M], Data8[M], Data9[M], Data10
o As the RADIUS packet exceeds the maximum allowed length (8
attributes), the AS truncates the packet to generate the first
chunk. This chunk only includes the attributes that cannot be
included in Access-Challenge packets. In this example they are
the User-Name, the Service-Type and the Framed-IP-Address. The
Service-Type is changed to "Authorize-Only", and a State attribute
is included.
Access-Accept-1 = User-Name, Service-Type[Authorize-Only],
Framed-IP-Addres, State1
o When the NAS receives the Access-Accept, it determines, based on
the Service-Type=Authorize-Only, that an additional exchange is
required. Thus, it generates a new Access-Request packet
containing the received State attribute.
Access-Request-1 = State1
o The AS then generates a new chunk with part of the remaining
attributes to be sent. As they do not fit into a single chunk, a
More-Data-Pending attribute and a new State attribute are also
included.
Access-Challenge-1 = Data1[M], Data2[M], Data3[M], Data4[M],
Data5[M], Data6[MT], More-Data-Pending, State2
o The NAS determines the received packet is part of a larger one
(i.e. it is a chunk) due to the presence of the More-Data-Pending
attribute, hence it requests the rest of the data by sending a new
Access-Request packet including the received State attribute.
Access-Request-2 = State2
o Finally, the AS includes the rest of the attributes into the final
Access-Accept packet. This packet also includes the original
Service-Type for the user.
Access-Accept-2 = Data7[M], Data8[M], Data9[M], Data10,
Service-Type[X]
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o On reception of this last packet, the NAS can process the totality
of the received attributes as if they all had been received into a
single RADIUS packet larger than 4 KB.
The following figure depicts the exchange of chucks between the NAS
and the AS.
+-+-+-+-+ +-+-+-+-+
| NAS | | AS |
+-+-+-+-+ +-+-+-+-+
| |
| Access-Accept(User-Name,Service-Type[AuthOnly], |
| Framed-IP-Addres,State1) |
|<--------------------------------------------------------|
| |
| Access-Request(State1) |
|-------------------------------------------------------->|
| |
| Access-Challenge(Data1[M],Data2[M],Data3[M], |
| Data4[M],Data5[M],Data6[MT], |
| More-Data-Pending,State2) |
|<--------------------------------------------------------|
| |
| Access-Request(State2) |
|-------------------------------------------------------->|
| |
| Access-Accept(Data7[M],Data8[M],Data9[M], |
| Data10,Service-Type[X]) |
|<--------------------------------------------------------|
Figure 4: Fragmented Access-Accept packet
7. Security Considerations
8. IANA Considerations
This document has no actions for IANA.
9. Normative References
[I-D.ietf-radext-radius-extensions]
DeKok, A. and A. Lior, "Remote Authentication Dial In User
Service (RADIUS) Protocol Extensions",
draft-ietf-radext-radius-extensions-04 (work in progress),
January 2012.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC6158] DeKok, A. and G. Weber, "RADIUS Design Guidelines",
BCP 158, RFC 6158, March 2011.
Authors' Addresses
Alejandro Perez-Mendez (Ed.)
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100
Spain
Phone: +34 868 88 46 44
Email: alex@um.es
Rafa Marin-Lopez
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100
Spain
Phone: +34 868 88 85 01
Email: rafa@um.es
Fernando Pereniguez-Garcia
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100
Spain
Phone: +34 868 88 78 82
Email: pereniguez@um.es
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Gabriel Lopez-Millan
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
Murcia, 30100
Spain
Phone: +34 868 88 85 04
Email: gabilm@um.es
Diego R. Lopez
Telefonica I+D
Don Ramon de la Cruz, 84
Madrid, 28006
Spain
Phone: +34 913 129 041
Email: diego@tid.es
Alan DeKok
Network RADIUS
15 av du Granier
Meylan, 38240
France
Phone: +34 913 129 041
Email: aland@networkradius.com
URI: http://networkradius.com
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