>The question that's on my mind is where you have an area which has multiple
>ABRs. Do the internal routers simply compare the metrics to the respective
>ABRs and make their routing decision based on that comparison?
>
>BJ
In a totally stubby area, or in a stubby area where there is no
explicit inter-area route to the destination, yes.
>
>
>-----Original Message-----
>From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]]
>Sent: Wednesday, August 15, 2001 9:44 AM
>To: [EMAIL PROTECTED]
>Subject: Re: OSPF Distance Vector in the backbone? [7:16120]
>
>
>While I agree completely with Peter's statements, I think there may be two
>issues being mingled.
>
>Area 0.0.0.0, especially when there are no backbone-only routers, uses a
>DV-like algorithm to
>propagate inter-area and exterior routes. There's no use for a Dijkstra.
>
>Inside a nonzero area, the Dijkstra algorithm only computes intra-area
>routes, with a computational
>workload on the order of the square of the number of routes plus the
>logarithm of the number of routers.
>Inter-area and external routes are added to the routing table of that area
>as a second step, the workload for
>which is linear with the number of non-intra-area routes.
>
>At 08:55 AM 8/15/2001 -0400, you wrote:
>>Hey Ralph,
>>
>>This statement is quite true. Is there an area you wish to break down more
>>fully?
>>
>>For support, see the draft-ietf-ospf-abr-alt-04.txt which includes the
>>following text:
>>
>>In OSPF domains the area topology is restricted so that there must be
>> a backbone area (area 0) and all other areas must have either
>> physical or virtual connections to the backbone. The reason for this
>> star-like topology is that OSPF inter-area routing uses the
>> distance-vector approach and a strict area hierarchy permits
>> avoidance of the "counting to infinity" problem. OSPF prevents
>> inter-area routing loops by implementing a split-horizon mechanism,
>> allowing ABRs to inject into the backbone only Summary-LSAs derived
>> from the intra-area routes, and limiting ABRs' SPF calculation to
>> consider only Summary-LSAs in the backbone area's link-state
>> database.
>>
>>
>>*********** REPLY SEPARATOR ***********
>>
>>On 8/15/2001 at 12:12 AM Ralph Fudamak wrote:
>>
>> >Question about OSPF and LSA type 3 behavior. Doyle in Routing TCP/IP
vol
>> >1:
>> >
>> > "When another router receives a Network Summary LSA from an ABR, it
>> >does
>> >not run the SPF algorithm. Rather it simply adds the cost of the route
>to
>> >the ABR and the cost included in the LSA. A route to the advertised
>> >destination, via the ABR, is entered into the route table along with the
>> >calculated cost. This behavior - depending on an intermediate router
>> >instead of determining the full route to the destination - is distance
>> >vector behavior. So, while OSPF is a link state protocol within an
area,
>> >it
>> >uses a distance vector algorithm to find inter-area routes." (pg
474,475)
>> >
>> >Please enlighten me.
>> >
>> >TIA,
>> >Ralph
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=16288&t=16120
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