[c-nsp] OSPF area design question

[Howard C. Berkowitz]

At 9:14 AM -0400 8/31/04, Peter van Oene wrote:
>At 04:41 PM 8/30/2004, Dan Armstrong wrote:
>>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...
>
>spf comes to mind.


SPF is obviously a consideration, but another consideration: does the 
NSSA have more than one ABR? If so, the other routers do need to know 
about it so they can pick closest exit.

>
>
>>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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