RADIUS attribute from rfc3162

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Framed-IPv6-Route

This Attribute provides routing information to be configured for
      the user on the NAS.  It is used in the Access-Accept packet and
      can appear multiple times.

   A summary of the Framed-IPv6-Route 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 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
   |     Type      |    Length     |  Text ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Type

      99 for Framed-IPv6-Route

   Length

      >=3

   Text

      The Text field is one or more octets, and its contents are
      implementation dependent.  The field is not NUL (hex 00)
      terminated.  It is intended to be human readable and MUST NOT
      affect operation of the protocol.

      For IPv6 routes, it SHOULD contain a destination prefix optionally
      followed by a slash and a decimal length specifier stating how
      many high order bits of the prefix to use.  That is followed by a
      space, a gateway address, a space, and one or more metrics
      (encoded in decimal) separated by spaces.  Prefixes and addresses
      are formatted as described in .  For example,
      "2000:0:0:106::/64 2000::106:a00:20ff:fe99:a998 1".Whenever the gateway address is the IPv6 unspecified address the
      IP address of the user SHOULD be used as the gateway address.  The
      unspecified address can be expressed in any of the acceptable
      formats described in .  For example, "2000:0:0:106::/64 :: 1".

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