From: Peter Van Oene (petvan@gmail.com)
Date: Mon Sep 26 2005 - 13:10:13 GMT-3
Just for the record, the below bit is not correct. OSPF doesn't track area
hop counts or anything of the like. I just noticed another post which
correctly points out where in the spec the answer is given, that being that
ABR's don't use non 0 type-3's for reachability.
>
> -----Original Message-----
> From: Stefan Grey [mailto:examplebrain@hotmail.com]
> Sent: Sunday, September 25, 2005 12:24 PM
> To: Chris Lewis [chrlewis@cisco.com]
> Subject: RE: VERY INTERESTING OSPF behaviour??
>
> Hello Chris,
>
> Below is some additional info. Look my answer to the group above the
> word END, END. And than the answer of TIM.
>
> At the moment his answer on my question is best. If that about what he
> is writing is true than it would solve my question. He tells that there
> is another criteria about OSPF: the number of AREAs. Have heared
> something about it?? Is that true?? I havent ever heared about it by
> myself.
>
>
> Thanks,
>
>
>
> TIM wrote:
> 1
> 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
>
>
> Hello guys,
> thanks to all how replyed on my problem. Here are some new things:
>
> 1st. I don't think that it is a problem that the intra area route is
> more prefered than the inter area routes. This is because a I think both
> routes area Inter ARea. One is through Area 0 second through Area 1 and
> the origin of the route is in Area 3.
>
> 2nd. What happens, just for
> >kicks, if you add on R2 "area 1 virtual-link <R3 RID>" and on R3 "area
> >1 virtual-link <R2 RID>"?What happens, just for
>
> When I configrued the virtual link between R3 and R2. The route through
> R2 bacame more prefereble as it should be. (the metric 76).
>
> When both routes area through area 0 the second route is more
> preferable.
>
> 3rd. The behaviour is like following: The router chooses the route
> through Area 0 to Area 3. The router thinks that it is better than to
> Area 1 than to ARea 0 and than to area 3.
> Although both routes area interarea and the metric for second route is
> better.
>
> Strange not?? What do you think about it?? Maybe OSPF have something
> like as-path for areas :):) ??
>
> So to sum up. How ospf makes a dicision about the best route???
>
> 1. Inter area , intra area, outside route 2. AD 3. Metric
>
> Which other criterea in my case??
>
> Thanks,
>
>
> END END END
>
> >From: chrlewis@cisco.com
> >To: "Stefan Grey" <examplebrain@hotmail.com>
> >Subject: RE: VERY INTERESTING OSPF behaviour??
> >Date: Sun, 25 Sep 2005 11:51:15 -0400
> >
> >OPSF prefers the following
> >
> >Inter area routes
> >Intra area routes
> >E1 routes
> >E2 routes
> >N1 routes
> >N2 routes
> >
> >All before it looks at the metric.
> >
> >If this does not answer your question, please forward the configs and
> >I'll take a look.
> >
> >Chris
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>
> >Stefan Grey
> >Sent: Sunday, September 25, 2005 9:25 AM
> >To: ccielab@groupstudy.com
> >Subject: VERY INTERESTING OSPF behaviour??
> >
> > Hi, group,
> >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??
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