RADIUS attribute from rfc7268

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EAP-Peer-Id

The EAP-Peer-Id Attribute contains a Peer-Id generated by the EAP
      method.  Exactly how this name is used depends on the link layer
      in question.  See  for more discussion.  The EAP-Peer-Id
      Attribute MAY be included in Access-Request, Access-Accept, and
      Accounting-Request packets.  More than one EAP-Peer-Id Attribute
      MUST NOT be included in an Access-Request; one or more EAP-Peer-Id
      Attributes MAY be included in an Access-Accept.It should be noted that not all link layers use this name, and
      existing EAP method implementations do not generate it.  Since the
      NAS operates as a pass-through in EAP , it cannot know
      the EAP-Peer-Id before receiving it from the RADIUS server.  As a
      result, an EAP-Peer-Id Attribute sent in an Access-Request MUST
      only contain a single NUL character.  A home RADIUS server
      receiving an Access-Request with an EAP-Peer-Id Attribute
      containing anything other than a single NUL character MUST
      silently discard the attribute.  In addition, the home RADIUS
      server SHOULD include one or more EAP-Peer-Id Attributes in an
      Access-Accept only if an EAP-Peer-Id Attribute was present in the
      Access-Request.  If a NAS receives EAP-Peer-Id Attribute(s) in an
      Access-Accept without having included one in an Access-Request,
      the NAS SHOULD silently discard the attribute(s).  A summary of
      the EAP-Peer-Id Attribute format is shown below.  The fields are
      transmitted from left to right.

       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       |            String...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      175

   Length

      >=3

   String

      The String field is one or more octets, containing an EAP Peer-Id
      exported by the EAP method.  For details, see.  A robust implementation SHOULD support the field as
      undistinguished octets.  Only a single EAP Peer-Id may be included
      per attribute.

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