From: Jamie Caesar (jamie.caesar@gmail.com)
Date: Sun Sep 25 2005 - 22:13:24 GMT-3
I would agree with that. It is OSPF behavior to reach all other areas
through area 0, so no matter what the metrics are for the route through area
1, it will never be chosen as long as a connection to area 0 exists. As you
said, once the link to area 0 goes down it is no longer an ABR and must use
the route through the only area it is still a member of -- area 1.
Jamie
CCIE #14995
On 9/25/05, Rich Kettelson <rkettelson@mn.rr.com> wrote:
>
> 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 <http://1.1.6.6/32> [110/10001] via
1.1.35.5<http://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 <http://1.1.6.6/32> [110/76] via
1.1.23.2<http://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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