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Quoting dhcpd.conf.5 about the optionAL EUI-64 feature:

          use-eui-64 flag;

          The  use-eui-64  flag,  if enabled, instructs the server to con-
          struct an address using the client's EUI-64  DUID  (Type  3,  HW
          Type  EUI-64), rather than creating an address using the dynamic
          algorithm.  This means that a given DUID  will  always  generate
          the  same  address for a given pool and further that the address
          is guaranteed to be unique to that DUID.  The IPv6 address  will
          be  calculated from the EUI-64 link layer address, conforming to
          RFC 2373, unless there is a host declaration for the  client-id.

          The range6 statement for EUI-64 must define full /64 bit ranges.
          Invalid ranges will be flagged during configuration  parsing  as
          errors.  See the following example:

              subnet6 fc00:e4::/64 {
                  use-eui-64 true;
                  range6 fc00:e4::/64;
              }

          The  statement may be specified down to the pool level, allowing
          a mixture of dynamic and EUI-64 based pools.

          During lease file parsing, any leases which  map  to  an  EUI-64
          pool, that have a non-EUI-64 DUID or for which the lease address
          is not the EUI-64 address for that DUID in that  pool,  will  be
          discarded.

          If a host declaration exists for the DUID, the server grants the
          address (fixed-prefix6, fixed-address6) according  to  the  host
          declaration, regardless of the DUID type of the client (even for
          EUI-64 DUIDs).

          If a client request's an EUI-64 lease for a given  network,  and
          the  resultant  address  conflicts with a fixed address reserva-
          tion, the server will send the client a "no addresses available"
          response.

          Any client with a non-conforming DUID (not type 3 or not hw type
          EUI-64) that is not linked to a host declaration, which requests
          an  address  from an EUI-64 enabled pool will be ignored and the
          event will be logged.

          Any client with a non-conforming DUID (not type 3 or not hw type
          EUI-64) that is not linked to a host declaration, which requests
          an  address  from an EUI-64 enabled pool will be ignored and the
          event will be logged.

          Pools that are configured for EUI-64 will be skipped for dynamic
          allocation.   If  there  are no pools in the shared network from
          which to allocate, the client  will  get  back  a  no  addresses
          available status.

          On  an  EUI-64  enabled  pool, any client with a DUID 3, HW Type
          EUI-64, requesting a solicit/renew and including IA_NA  that  do
          not match the EUI-64 policy, they will be treated as though they
          are "outside" the subnet for a given client message:

              Solicit - Server will advertise with  EUI-64  ia  suboption,
          but with rapid
              commit off
              Request  - Server will send "an address not on link status",
          and no ia
              suboption Renew/Rebind -  Server  will  send  the  requested
          address ia
              suboption with lifetimes of 0, plus an EUI-64 ia

          Whether or not  EUI-64 based leases are written out to the lease
          database may be controlled by persist-eui-64-leases statement.

Added to ISC DHCP as an optional feature on customer request. Can be ported to Kea.