On Oct 6, 2009, at 11:22 AM, Joakim Tjernlund wrote:

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|---
= . = +---+ = . = . = +----+ = +---+
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.
=

Do you have a choice here? I read the RFC that if = the P2P link has
a host route (mask =3D = 255.255.255.255) you have to advertise a stub
link to the other router's interface = address.

=46rom RFC = 2328:

            12.4.1.1.  Describing =
point-to-point interfaces

                For point-to-point interfaces, one or more link
                descriptions are added to the router-LSA as follows:

                o   If the neighboring router is fully adjacent, add a
                    Type 1 link (point-to-point). The Link ID should be
                    set to the Router ID of the neighboring router. For
                    numbered point-to-point networks, the Link Data
                    should specify the IP interface address. For
                    unnumbered point-to-point networks, the Link Data
                    field should specify the interface's MIB-II [Ref8]
                    ifIndex value. The cost should be set to the output
                    cost of the point-to-point interface.

                o   In addition, as long as the state of the interface
                    is "Point-to-Point" (and regardless of the
                    neighboring router state), a Type 3 link (stub
                    network) should be added. There are two forms that
                    this stub link can take:

                    Option 1
                        Assuming that the neighboring router's IP
                        address is known, set the Link ID of the Type 3
                        link to the neighbor's IP address, the Link Data
                        to the mask 0xffffffff (indicating a host
                        route), and the cost to the interface's
                        configured output cost.[15]

                    Option 2
                        If a subnet has been assigned to the point-to-
                        point link, set the Link ID of the Type 3 link
                        to the subnet's IP address, the Link Data to the
                        subnet's mask, and the cost to the interface's
                        configured output cost.[16]

Hope this =
helps,

Acee

Hope = this helps,
Acee

=