Issue: Treatment of null Identity Response

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

RFC 3748 and RFC 2865 appear to disagree on the subject of whether a 
response to an EAP-Request/Identity can be an EAP-Response/Identity packet 
with no data.

RFC 3748 Section 5.1 says:

  Type

     1

  Type-Data

     This field MAY contain a displayable message in the Request,
     containing UTF-8 encoded ISO 10646 characters [RFC2279].  Where
     the Request contains a null, only the portion of the field prior
     to the null is displayed.  If the Identity is unknown, the
     Identity Response field should be zero bytes in length.  The
     Identity Response field MUST NOT be null terminated.  In all
     cases, the length of the Type-Data field is derived from the
     Length field of the Request/Response packet.

So according to RFC 3748, it is possible to have an Identity Response field 
that is zero bytes in length, if the identity is not known.

However, RFC 2865 Section 5.1 says:

5.1.  User-Name

  Description

     This Attribute indicates the name of the user to be authenticated.
     It MUST be sent in Access-Request packets if available.

     It MAY be sent in an Access-Accept packet, in which case the
     client SHOULD use the name returned in the Access-Accept packet in
     all Accounting-Request packets for this session.  If the Access-
     Accept includes Service-Type = Rlogin and the User-Name attribute,
     a NAS MAY use the returned User-Name when performing the Rlogin
     function.

  A summary of the User-Name Attribute format is shown below.  The
  fields are transmitted from left to right.

   0                   1                   2
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
  |     Type      |    Length     |  String ...
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

  Type

     1 for User-Name.

  Length

     >= 3

  String

     The String field is one or more octets.  The NAS may limit the
     maximum length of the User-Name but the ability to handle at least
     63 octets is recommended.

     The format of the username MAY be one of several forms:
     text      Consisting only of UTF-8 encoded 10646 [7] characters.
     network access identifier

Since the User-Name must be at least 3 bytes in length, a zero-length String 
field is not acceptable.

Question:  What does a RADIUS client do if it receives an 
EAP-Identity/Response with no data?



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