This attribute specifies the link model to use when the media type for
this IpPort is PPP (Point to Point Protocol). A value of
localAreaNetwork causes IP to treat this IpPort like a LAN. A value of
pointToPoint causes IP to treat this IpPort like two directly connected
IP hosts. A value of loopback causes IP to treat this IpPort similar to a
point-to-point, but the destination and source points are the same
providing an always up interface.