[c-nsp] OSPF area design question

[Dan Armstrong]

We too have a similar situation.  We opted to make a whackload of OSPF areas.  
I am very curious if this design is going to eat up some resource 
unnecessarily.

I can't quite figure out why in a "real"  NSSA scenario that other routers in 
the same area need to know anything about other routers in the stub area, 
since the only path anywhere else is up to the distribution layer anyway, 
which is handled with the default route that gets advertised down...

Dan.



On Monday 30 August 2004 16:37, Marcel Lammerse wrote:
> Ok, if you have that area 1 with 15 routers. Would it be a good idea to
> keep them all in one area, or would it make sense to assign 15
> different area numbers and make each of them a separate area (NSSA in
> this case). Because, I figured, an update from one of the router will
> be flooded throughout the entire area which is totally unnecessary.
>
> I like to know whether the extra configuration and administrative
> overhead is worth saving on unnecessary update floods and cpu cycles
> processing them.
>
> On Aug 30, 2004, at 9:47 PM, James Hampton wrote:
> > The way I'm reading this is that you have three hub routers connected
> > like  points on a triangle, with each point having 15 or so spokes? If
> > this is the case I would make the top router(or the one in the middle)
> > area 0 and the others 1 and 2 or what ever numbering scheme you come
> > up with. Than address each area with contiguous blocks so that you can
> > summarize and keep the routing table as small as possible. The spokes
> > could be "stubby" sense they have only one way out.
> >
> > James
> >
> >
> > On Mon, 30 Aug 2004 17:54:35 +0200 (CEST), Marcel Lammerse
> >
> > <lammerse at xs4all.nl> wrote:
> >> Hi,
> >>
> >> I have a hub-and-spoke network, for which I'd like to use OSPF as a
> >> routing protocol. The spoke sites will advertise their networks to
> >> the hub and receive a default route from the hub.
> >>
> >> A common piece of advice in OSPF design literature, is to use
> >> different
> >> area numbers to prevent unnecessary LSA updates from flooding to
> >> routers
> >> that don't need the updates and to avoid the cpu processing overhead.
> >>
> >> The total network has some 50 routers.  There are 3 inter-connected
> >> hubs
> >> and some 15 routers per hub. The way I see it, I can do two things:
> >>
> >> 1.      assign a lot of area numbers to prevent the LSAs from
> >> propagating
> >>        through to routers that don't need them. However, this leads
> >> to a
> >>        relatively complex configuration.
> >>
> >> 2.      accept the, potentially small, bandwidth waste and don't care
> >>        about the cpu overhead (we're talking 2600XMs here).
> >>
> >> Option 1 just doesn't seem worth it. Could someone provide some
> >> advice,
> >> experience or tips?
> >>
> >> Thanks.
> >>
> >> -Marcel
> >>
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