The simplest configuration that combines DECnet-Plus link state
 subnetworks connected to DECnet Phase IV routing vector subnetworks
 is one in which only two subnetworks are connected, with only one
 area in each subnetwork.  For example:

  +----------+ Interphase  +--------------+
  |Link State| Link circuit|Routing Vector|
  |L2 router |- - - - - - -|L2 router     |
  |in Area 1 |             |in Area 2     |
  +----------+             +--------------+

 In this case, no interphase links are required, since adjacent areas
 will automatically configure to each other.

 If either subnetwork contains more than one area, or if multiple
 subnetworks are interconnected, then interphase links must be created to
 provide routing information about the non-adjacent areas.