[OSPF] ospf backbone area

[Sinbad <sinbad.sinbad at gmail.com>]

             ...........................
             .   +                     .

             .   | 3+---+              .      N12      N14
             . N1|--|RT1|\ 1           .        \ N13 /

             .   |  +---+ \            .        8\ |8/8
             .   +         \ ____      .          \|/

             .              /    \   1+---+8    8+---+6
             .             *  N3  *---|RT4|------|RT5|--------+

             .              \____/    +---+      +---+        |
             .    +         /      \   .           |7         |

             .    | 3+---+ /        \  .           |          |
             .  N2|--|RT2|/1        1\ .           |6         |

             .    |  +---+            +---+8    6+---+        |
             .    +                   |RT3|------|RT6|        |

             .                        +---+      +---+        |
             .                      2/ .         Ia|7         |

             .                      /  .           |          |
             .             +---------+ .           |          |

             .Area 1           N4      .           |          |
             ...........................           |          |

          ..........................               |          |
          .            N11         .               |          |

          .        +---------+     .               |          |
          .             |          .               |          |    N12

          .             |3         .             Ib|5         |6 2/
          .           +---+        .             +----+     +---+/

          .           |RT9|        .    .........|RT10|.....|RT7|---N15.
          .           +---+        .    .        +----+     +---+ 9    .

          .             |1         .    .    +  /3    1\      |1       .
          .            _|__        .    .    | /        \   __|_       .

          .           /    \      1+----+2   |/          \ /    \      .
          .          *  N9  *------|RT11|----|            *  N6  *     .

          .           \____/       +----+    |             \____/      .
          .             |          .    .    |                |        .

          .             |1         .    .    +                |1       .
          .  +--+   10+----+       .    .   N8              +---+      .

          .  |H1|-----|RT12|       .    .                   |RT8|      .
          .  +--+SLIP +----+       .    .                   +---+      .

          .             |2         .    .                     |4       .
          .             |          .    .                     |        .

          .        +---------+     .    .                 +--------+   .
          .            N10         .    .                     N7       .

          .                        .    .Area 2                        .
          .Area 3                  .    ................................

          ..........................



1) In the above ospf topology according to ospf rfc 2328 in section 3.4, it states that 

   "Note that a failure of the line between Routers RT6 and RT10

   will cause the backbone to become disconnected."

Though there is router RT7 in area 2 still connected to the backbone.It confused my understanding of 
disconnected backbone area. Can someone shed some light on this.


2) why should routers connected by a point to point link having interface addresses assigned,
  should advertise a stub link a stub connection to the other router's interface address.


thanks