RADIUS attribute from rfc2865

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Login-LAT-Port

This Attribute indicates the Port with which the user is to be
      connected by LAT.  It MAY be used in Access-Accept packets, but
      only when LAT is specified as the Login-Service.  It MAY be used
      in an Access-Request packet as a hint to the server, but the
      server is not required to honor the hint.

   A summary of the Login-LAT-Port 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

      63 for Login-LAT-Port.

   Length

      >= 3String

      The String field is one or more octets, and contains the identity
      of the LAT port to use.  The LAT Architecture allows this string
      to contain $ (dollar), - (hyphen), . (period), _ (underscore),
      numerics, upper and lower case alphabetics, and the ISO Latin-1
      character set extension.  All LAT string comparisons are case
      insensitive.

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