RADIUS attribute from rfc2865

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Framed-AppleTalk-Link

This Attribute indicates the AppleTalk network number which should
      be used for the serial link to the user, which is another
      AppleTalk router.  It is only used in Access-Accept packets.  It
      is never used when the user is not another router.

   A summary of the Framed-AppleTalk-Link 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     |             Value
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Value (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      37 for Framed-AppleTalk-Link.

   Length

      6

   Value

      The Value field is four octets.  Despite the size of the field,
      values range from 0 to 65535.  The special value of 0 indicates
      that this is an unnumbered serial link.  A value of 1-65535 means
      that the serial line between the NAS and the user should be
      assigned that value as an AppleTalk network number.

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