IPv4 address
Click on the red underlined text to get to the source
... an IPsec tunnel mode interface include the need to obtain an IPv4
address and other configuration parameters appropriate to the class
...
... following additional capabilities may be desirable:
a. integration with existing IPv4 address management facilities
b. support for address ...
... compatibility and integration with existing addressing
implementations and IPv4 address management software.
...
... LAN interface, the chaddr field SHOULD be
determined by concatenating x'4000', the IPv4 address of the
interface supplying network ...
... interface number)
SHOULD be persistent between reboots, so that the chaddr value
will be persistent across reboots if the assigned IPv4 address
remains consistent.
...