[c-nsp] Different Areas OSPF Paths

[Shakeel Ahmad]

> The shortest path algorithm really says 'shortest path via one
> area, then shortest path via area 0, and finally shortest path
> via other area'.

Thanks got the point, please correct me if i am wrong:

For an ABR - Area 3 or Area 4 is an Intra-Area so thats why its choosing it
directly while RFC also holds true ... shuh cleared things up... Now
questions arrises, what should be the best practice .. like an example : (I
am running a voice card on ABR-2-Site-A) and if i am giving voice
destination a loopback IP address of the Site-B router which is being
learned by OSPF.... Now if the Provider-ABR-2 goes down , it'll work and
will shift to other provider by Area 0 --- BUT what is there is congestion
and you wan't to administratively route traffic towards other provider
(concidering limitation is of a physical T1 voice card in ABR-2-Site-A)


I coul'd have make it whole AREA 0 , but it won't scale and break the
moduler design of per site...

Also i just read you should'nt run more than TWO different OSPF Area's on an
ABR ... As database will be very huge... in my case i have to use edge
router and have to connect around 6/7 sites via this design... do you guys
see any issue here.


thanks very much for help...





On 9/7/06, Asbjorn Hojmark - Lists <lists at hojmark.org> wrote:
>
> > Route-Site-A-2 is the lowest cost to reach Site-B , On Core
> > router at Site-A you'll see Router-Site-A-2 and Site-B as a
> > selected path....but when you go to any ABR... you'll see its
> > own Tunnel as the best exit path via OSPF, although other ABR's
> > are recieving shortest path via OSPF neighbours.
>
> The shortest path algorithm really says 'shortest path via one
> area, then shortest path via area 0, and finally shortest path
> via other area'.
>
> Since each ABR has a connection to both area 0, 3 and 4, they'll
> send traffic from 3 to 4 via their own direct connection to 4.
> They will *not* send the traffic via area 0 as that would not be
> the shortest path.
>
> > Another question is: Area-3 doesn't wantes to recieve routes
> > from Area-4 and vice versa but connection to Area 0, is
> > distributing the routes/flooding to both these areas.
> >
> > I have tried making both Area 3 & 4 a stub but it's not
> > helping...
>
> You have to make the areas totally stubby if you don't want any
> routes flooded from area to area. Then Router-Site-C and Router-
> Site-B will only see their own respective area's routes and a
> default.
>
> -A
>
>