RADIUS attribute from rfc2865

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NAS-Identifier

This Attribute contains a string identifying the NAS originating
      the Access-Request.  It is only used in Access-Request packets.
      Either NAS-IP-Address or NAS-Identifier MUST be present in an
      Access-Request packet.

      Note that NAS-Identifier MUST NOT be used to select the shared
      secret used to authenticate the request.  The source IP address of
      the Access-Request packet MUST be used to select the shared
      secret.

   A summary of the NAS-Identifier 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

      32 for NAS-Identifier.

   Length

      >= 3String

      The String field is one or more octets, and should be unique to
      the NAS within the scope of the RADIUS server.  For example, a
      fully qualified domain name would be suitable as a NAS-Identifier.

      The actual format of the information is site or application
      specific, and a robust implementation SHOULD support the field as
      undistinguished octets.

      The codification of the range of allowed usage of this field is
      outside the scope of this specification.

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