From: Kumar Raja-Q16843 (Raja.Kumar@motorola.com)
Date: Sun Sep 25 2005 - 14:13:15 GMT-3
We had an issue in our core network too, we have two 6509s (lets say A and B) in redundant having a ISL trunk between them. If any element connected to the one of the 6509s (A) goes down, it wasn't using the other 6509 (B) having redundant link connected to the same element, instead it was using SUN management station (Gate D for OSPF) to reach the other 6509 (B) just because the SUN machine was different area, then we had to create a loopback interface in the each of 6509 in different area so as to use the ISL trunk between them.
This scenario clearly indicates the preference of OSPF is Inter-area.
Hope this helps.
Regards,
Raja
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Javier Tomi
Sent: Sunday, September 25, 2005 9:51 PM
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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