snMspsDhcpClient6IfDuidType

A DUID consists of a two-octet type code represented in network byte
order, followed by a variable number of octets that make up the
actual identifier. The following types are currently defined:
          
1   Link-layer address plus time
2   Vendor-assigned unique ID based on Enterprise Number
3   Link-layer address
          
DUID Based on Link-layer Address plus Time [DUID-LLT]
          
This type of DUID consists of a two octet type field containing the
value 1, a two octet hardware type code, four octets containing a
time value, followed by link-layer address of any one network
interface that is connected to the DHCP device at the time
that the DUID is generated.  The time value is the time that the
DUID is generated represented in seconds since midnight
(UTC), January 1, 2000, modulo 2^32.
          
The following diagram illustrates the format of a DUID-LLT:
          
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               1               |    hardware type (16 bits)    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        time (32 bits)                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.                                                               .
.             link-layer address (variable length)              .
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          
          
The choice of network interface can be completely arbitrary, as long
as that interface provides a globally unique link-layer address for
the link type, and the same DUID-LLT SHOULD be used in configuring
all network interfaces connected to the device, regardless of which
interface's link-layer address was used to generate the DUID-LLT.
          
Clients and servers using this type of DUID MUST store the
DUID-LLT in stable storage, and MUST continue to use this DUID-LLT even
if the network interface used to generate the DUID-LLT is removed.
Clients and servers that do not have any stable storage MUST NOT
use this type of DUID.
          
Clients and servers that use this DUID SHOULD attempt to configure
the time prior to generating the DUID, if that is possible, and MUST
use some sort of time source (for example, a real-time clock) in
generating the DUID, even if that time source could not be configured
prior to generating the DUID.  The use of a time source makes it
unlikely that two identical DUID-LLTs will be generated if the
network interface is removed from the client and another client then
uses the same network interface to generate a DUID-LLT.  A collision
between two DUID-LLTs is very unlikely even if the clocks have not
been configured prior to generating the DUID.
          
This method of DUID generation is recommended for all general purpose
computing devices such as desktop computers and laptop computers, and
also for devices such as printers, routers, and so on, that contain
some form of writable non-volatile storage.
          
DUID Assigned by Vendor Based on Enterprise Number [DUID-EN]
          
This form of DUID is assigned by the vendor to the device.  It
consists of the vendor's registered Private Enterprise Number as
maintained by IANA [6] followed by a unique identifier assigned by
the vendor. 
          
The following diagram summarizes the structure of a DUID-EN:
          
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               2               |       enterprise-number       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   enterprise-number (contd)   |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
.                           identifier                          .
.                       (variable length)                       .
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          
The source of the identifier is left up to the vendor defining it,
but each identifier part of each DUID-EN MUST be unique to the
device that is using it, and MUST be assigned to the device at the time
it is manufactured and stored in some form of non-volatile
storage. The generated DUID SHOULD be recorded in non-erasable storage. 
          
DUID Based on Link-layer Address [DUID-LL]:-
          
This type of DUID consists of two octets containing the DUID type 3,
a two octet network hardware type code, followed by the link-layer
address of any one network interface that is permanently connected to
the client or server device.
          
The following diagram illustrates the format of a DUID-LL:
          
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               3               |    hardware type (16 bits)    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.                                                               .
.             link-layer address (variable length)              .
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          
The choice of network interface can be completely arbitrary, as long
as that interface provides a unique link-layer address and is
permanently attached to the device on which the DUID-LL is being
generated.  The same DUID-LL SHOULD be used in configuring all
network interfaces connected to the device, regardless of which
interface's link-layer address was used to generate the DUID.
          
DUID-LL is recommended for devices that have a permanently-connected
network interface with a link-layer address, and do not have
nonvolatile, writable stable storage.  DUID-LL MUST NOT be used by
DHCP clients or servers that cannot tell whether or not a network
interface is permanently attached to the device on which the DHCP
client is running.