From: Rich Kettelson (rkettelson@mn.rr.com)
Date: Sun Sep 25 2005 - 19:32:54 GMT-3
This appears to be normal OSPF behavior.
1. Intra-area route
2. Inter-area route
4. External route
The way I see it, is that R3 is a backbone router when the ISDN link is up,
but an area 1 router when ISDN is down.
I believe it's the topology change that causes change in route selected, not
the OSPF cost.
Anybody agree?
Rich
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Javier Tomi
Sent: Sunday, September 25, 2005 11:21 AM
To: Tim
Cc: 'Stefan Grey'; 'Group Study'
Subject: Re: Tim maybe you could help here??
I guess the decision process for OSPF is as follows:
(lets suppose that both prefixes are identical in terms of mask length)
1. Intra-area route
2. Inter-area route from backbone (which should be closer to the ABR
originating the LSA)
3. Inter-area route from another area
4. External route
In case of a tie, AD and metric enter into play
Could someone corroborate this?...
Javi
Tim wrote:
>Stefan,
>
>This brings up another aspect of ospf.
>
>Inter-area routing is determined like a distance vector IGP.
>
>Therefore, the fewer areas a route has to pass through, the more preferred
>it is.
>
>HTH, Tim
>
>-----Original Message-----
>From: Stefan Grey [mailto:examplebrain@hotmail.com]
>Sent: Sunday, September 25, 2005 11:24 AM
>To: ccie2be@nyc.rr.com
>Subject: RE: Tim maybe you could help here??
>
>Sure you are right about OSPF. But I think here is another problem. Since
>here both routes are Inter area. First route is through area 0, second
route
>
>is through area 1. But the route was originated from area 3.
>Thanks,
>
>Regards,
>
>
>
>
>
>>From: "Tim" <ccie2be@nyc.rr.com>
>>To: "'Stefan Grey'" <examplebrain@hotmail.com>
>>Subject: RE: Tim maybe you could help here??
>>Date: Sun, 25 Sep 2005 10:55:29 -0400
>>
>>Hey Stefan,
>>
>>I think you might be overlooking or forgetting something critical about
>>ospf.
>>
>>Ospf will always prefer an intra-area path over an inter-area path and
ospf
>>will always prefer an inter-area path over an external path.
>>
>>Cost doesn't matter here because that's only taken into account when both
>>paths are of the same type.
>>
>>I happened to learn this the hard way. I recall dealing with this same
>>issue you're raising here.
>>
>>This was while I was working on an IE lab - I forget which one but it's
>>from
>>the first IE workbook.
>>
>>HTH, Tim
>>
>>-----Original Message-----
>>From: Stefan Grey [mailto:examplebrain@hotmail.com]
>>Sent: Sunday, September 25, 2005 10:26 AM
>>To: ccie2be@nyc.rr.com
>>Subject: Tim maybe you could help here??
>>
>>
>> Hi Tim, thanks that you helped with my questions before. Maybe you
>>could
>>look on suche case as below?? It is one of the strangest things I
>>expirienced.
>>
>>
>>I see such behaviou the first time:
>>
>> R4
>> |
>> |
>> R1------R2
>> | __ |
>> | _|
>> | |
>> R3----
>>
>>
>>
>>
>>Between R1 and R4 is area 3, between router R3 and R1 area 0. Between R1
>>and
>>
>>R2 area 0. connection between R3 - R2 area 1. As to physical connections:
>>between R1 and R4 ethernet, between R3 and R2 ethernet. Between R1,R2 nbma
>>frame-relay, between R1 -R3 ISDN. Everything is configured correctly. R3
>>gets two routes about lo0 of R4 from R1 and R2.
>>on R1 is configured the ip ospf 9999 command to make this route less
>>preffereable than from R2. But what strange thing wee see:
>>
>>
>>O IA 1.1.6.6/32 [110/10001] via 1.1.35.5, 00:17:32, BRI0/0
>>I wonder why the less prefereble route is used?? Ok I turn of the bri0/0
>>interface
>>and look which other route I get from router R2.
>>
>>O IA 1.1.6.6/32 [110/76] via 1.1.23.2, 00:00:29, Ethernet0/1
>>This route is the same as previous but with much better metric. Why it is
>>not choosed?? But the worther one is choosed??
>>
>>
>>Thanks,
>>
>>The only one advantage of the route through R1 is that R1 - R3 is in
AREA0.
>>But as we know the route is choosed just in two criterias AD/ Metric.
>>I am totally confused with this.
>>
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