RADIUS attribute from rfc3162

---

NAS-IPv6-Address

This Attribute indicates the identifying IPv6 Address of the NAS
      which is requesting authentication of the user, and SHOULD be
      unique to the NAS within the scope of the RADIUS server.  NAS-
      IPv6-Address is only used in Access-Request packets.  NAS-IPv6-
      Address and/or NAS-IP-Address MAY be present in an Access-Request
      packet; however, if neither attribute is present then NAS-
      Identifier MUST be present.

   A summary of the NAS-IPv6-Address 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     |             Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                Address
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Address             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Type

      95 for NAS-IPv6-Address

   Length

      18

   Address

      The Address field is 16 octets.

---