Questions on RADIUS Extended attributes

["Bernard Aboba" <bernard_aboba@hotmail.com>]

At IETF 66, we discussed how to extend the RADIUS attribute space.  The 
consensus in the room as well as on the WG mailing list seems to be to focus 
on extending the space only, not adding functionality, along the lines that 
Avi had proposed:

http://www.watersprings.org/pub/id/draft-lior-radius-attribute-type-extension-00.txt

During IETF 66, there was some sentiment that the RADIUS Extended attribute 
should utilize a new RADIUS attribute value, rather than using a Vendor-Id 
value of zero (0) with the existing RADIUS VSA attribute (Type 26).

Taking that into account, find below a strawman proposal for what the 
Extended-Type attribute would look like.

Some questions:

a. Do we want an Extended-Type field of two or four octets?  If it is four 
octets, this would seem to imply that RADIUS attributes and Diameter AVPs 
share the same type space.  Will this work?  If it is two octets, we could 
reserve 65535 values within the existing Diameter attribute space for RADIUS 
Extended-Type attributes.   Opinions solicited.

b.  Should the second length field include the Extended-Type field or not?  
If it is included and Extended-Type is 4 octets, then this implies that the 
Value field could only be 251 octets.  If the second length field doesn't 
include Extended-Type, it could be as long as 255 octets, but then we'd need 
to allow Extended-Type attributes to be split among multiple RADIUS 
attributes.

c. Should we allow multiple Extended-Type attributes to be placed inside a 
single RADIUS attribute? This is OK for RADIUS VSAs, is there an issue here?


==================================================
Proposed Extended-Type Attribute Format


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |            Extended-Type
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Extended-Type           |    Length2    |    Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type

        TBD  (not 26)

     Length

        >= 7

     Extended-Type

        Four octets.

        Values <= 255: Reserved
        Values > 255:  To be allocated by IANA

     Length2

        0-255 (doesn't include the Extended-Type field)

     Value

        0 or more octets as defined by the Length2 field.

     More than one RADIUS Extended-Type attribute may be included within
     a RADIUS attribute of Type TBD.  If more than one RADIUS attribute
     of Type TBD is included, then they are to be concatenated (allowing
     an Extended-Type attribute to be split between two RADIUS attributes).



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