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Re: [OSPF] ospf backbone area

Hi Sinbad,
See inline.

On Oct 6, 2009, at 6:20 AM, Sinbad wrote:


             ...........................
             .   +                     .
             .   | 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.
I believe this issue has been raised before although I couldn't find an errata. The figure is incorrect. Network N8 should be in the backbone area rather than Area 2.
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.
This dates back to the fact that P2P links were represented as a host route to the destination network on BSD based systems. Those of you who are familiar with GateD will remember this. Note that there is also an option to represent/advertise P2P links as a subnets. Most if not all routers vendors advertise the subnet. 

Hope this helps,
Acee





thanks

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