From: chrlewis@cisco.com
Date: Sun Sep 25 2005 - 20:11:41 GMT-3
Stefan,
I have not heard of OSPF keeping track of the numbers of areas a path
travels through as a criteria, I do not know where that information
would be kept in the LSA. All non zero areas need to be connected to
area 0 and the route to all intra area routes is via area 0, so an OSPF
router will tend to select the route to an IA via its area 0 interface
(if it has one), rather than a non-area 0 interface, which is what you
see here.
Chris
-----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 [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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