Correction to my own post. I meant to say that the LSA type 5's flood domain wide,
not just area wide.
*********** REPLY SEPARATOR ***********
On 12/11/2000 at 12:12 PM Peter A van Oene wrote:
>It actually has little to do with physical topology (noted exception of NSSA). They
>real differentiator is which LSA's flow within the area, and ultimately, what level
>of knowledge does the area have about the outside world. The stub concept involves
>the trade off of sub optimal routing for less LSA flooding. In a large OSPF domain,
>a huge number of Type 5 LSA's can be created which will flood area wide. Sometimes,
>this can overwhelm the processing of a smaller area and hence the stub concept makes
>sense. The trade off is, without the first hand knowledge via LSA type 4's about
>where each ASBR lives, these routers in stub areas may not always take the fastest
>path toward a external prefix.
>
>Pete
>
>
>*********** REPLY SEPARATOR ***********
>
>On 12/11/2000 at 1:08 AM Chuck Larrieu wrote:
>
>>Can someone perhaps help educate me here. I have now seen this on a couple
>>of posts, did a bit of reading, and have learned that stub and totally
>>stubby areas are not necessarily limited to a single ingress/egress point.
>>I.e. can have more than one ABR.
>>
>>Area0-------Area1 area 1 is a stub area ( or totally stubby, depending
>>upon the LSA, summarization, and default route handling )
>>
>>Area0------Area1_ABR1
>> |------Area1_ABR2 still a stub area / totally stubby area
>>
>>What makes and area NOT a stub area? Is it only the summarization / LSA /
>>default route handling?
>>
>>Yes I understand the NSSA, with its ABSR connecting to an outside AS and
>>that information being passed into an OSPF domain in a particular manner.
>>
>>I guess the question is this: other than the NSSA, is EVERY OSPF area either
>>stub or totally stubby?
>>
>>Area0---------Area1-------|
>> | ABR?
>> |---------Area2--------|
>>
>>would the above layout make and area NOT stubby or totally stubby?
>>
>>Chuck
>>
>>-----Original Message-----
>>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
>>Peter A van Oene
>>Sent: Saturday, November 11, 2000 8:01 PM
>>To: [EMAIL PROTECTED]
>>Subject: Re: OSPF Totally Stubby Areas and area default-cost
>>
>> Totally stubby is a cisco nob that takes the concept of a stub area a step
>>further. In a stub area, only LSA types 1 (router) 2 (network) and 3
>> summary) flow within the area. Hence, no routing information concerning
>>prefixes outside of the OSPF domain is injected into the area. In a totally
>>stubby area, the flow of normal type 3 LSA's is halted as well. This leaves
>>the area with no information about any prefixes outside of the area. In
>>order to allow traffic to exit the area, a single type 3 LSA is propagated
>>by each ABR which advertises a default route. The default cost nob simply
>>allows you to set a cost for the route instead of using the standard OSPF
>>metric to the ABR itself.
>>
>>Hope this helps some
>>
>>Pete
>>
>>
>>*********** REPLY SEPARATOR ***********
>>
>>On 11/08/2000 at 4:29 PM Bob Hunter wrote:
>>
>>>Hi,
>>> I'm confused on the subject of totally stubby areas, and the command "area
>>>default-cost". From what I'm reading, one of the qualifications of a
>>totally
>>>stubby area is that if multiple exits (ABRs) exist, routing to outside the
>>>area does not have to take an optimal path. Does this mean that each router
>>>within the area picks the closest ABR as the gateway to everything outside
>>>the area, and that there is no way to control the default route? If so,
>>does
>>>that imply that the area default-cost is used for incoming routes? Would
>>>incoming routes even exits if the area was a totally stubby area?
>>>
>>> I would very much appreciate it if someone would please set me straight.
>>>
>>> Thank you.
>>>
>>>Bob Hunter, CCNA, CNE
>>>
>>>
>>>
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>>
>>
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>
>
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