Re: OSPF Path selection question

Q. How can I give preference to OSPF interarea routes over intra-area routes?

A. According to section 11 of RFC 2328 , the order of preference for
OSPF routes is:

intra-area routes, O

interarea routes, O IA

external routes type 1, O E1

external routes type 2, O E2

This rule of preference cannot be changed. However, it applies only
within a single OSPF process. If a router is running more than one
OSPF process, route comparison occurs. With route comparison, the
metrics and administrative distances (if they have been changed) of
the OSPF processes are compared. Route types are disregarded when
routes supplied by two different OSPF processes are compared.

On Sun, Mar 21, 2010 at 3:29 AM, mohamed kamar
<mohamed_kamar_at_hotmail.com> wrote:
> Thanks Ronnie;
> But the path the router is taking is having the higher cost I mean it's
> not the shortest path, It looks intra is preferred over the inter
> anyway regarding the cost, Is there a way to disable this feature from OSPF
> itself, I mean if i have a limitation stops me to install a new link in OSPF
> AREA 1, and i want to take Area 0 path for traffic symmetry reasons, Can i
> do this from the OSPF itself without adding new links, thanks
>
>
>
>
>> Date: Sat, 20 Mar 2010 19:16:47 -0400
>> Subject: Re: OSPF Path selection question
>> From: ronnie.angello_at_gmail.com
>> To: mohamed_kamar_at_hotmail.com
>> CC: ccielab_at_groupstudy.com
>>
>> Yes, it's expected if I understand your topology correctly. See rule
>> #3. You can get creative and change the behavior. Change the link
>> between R5 and R4 to area 1 or add a link between R5 and R2. That
>> type of thing...
>>
>> On Sat, Mar 20, 2010 at 7:00 PM, mohamed kamar
>> <mohamed_kamar_at_hotmail.com> wrote:
>> >
>> >
>> > Thanks Ronnie;
>> > The case here that it's taking area 1 path anyway regardless the cost,
>> > is
>> > it expected?, If yes, how to overcome this ? Thanks
>> >
>> >> Date: Sat, 20 Mar 2010 18:53:11 -0400
>> >> Subject: Re: OSPF Path selection question
>> >> From: ronnie.angello_at_gmail.com
>> >> To: mohamed_kamar_at_hotmail.com
>> >> CC: ccielab_at_groupstudy.com
>> >>
>> >> Metrics aside, consider OSPF path selection rules -
>> >>
>> >> 1) Take shortest path to area 0
>> >> 2) Take shortest path through area 0 without going through a non-zero
>> >> area
>> >> 3) Take shortest path to destination without going through area 0
>> >>
>> >> Thanks,
>> >> Ronnie
>> >>
>> >> On Sat, Mar 20, 2010 at 6:25 PM, mohamed kamar
>> >> <mohamed_kamar_at_hotmail.com> wrote:
>> >> > Hi Friends;
>> >> >
>> >> > Any one has idea what's going on in the below?
>> >> >
>> >> >
>> >> > R1
>> >> >
>> >> > | (BGP)
>> >> >
>> >> > |------------------------|
>> >> >
>> >> > R3---------------------R2
>> >> >
>> >> > | OSPF Area1 |
>> >> >
>> >> > R5-------------------- R4
>> >> >
>> >> > OSPF Area 0
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > -R1 is running BGP with R2 and R3
>> >> >
>> >> > -R2 is primary router So it's redistribute BGP into OSPF metric 100
>> >> > type
>> >> > E1
>> >> >
>> >> > -R3 is Secondry router So it's redistribute BGP into OSPF metric 200
>> >> > type E1
>> >> >
>> >> >
>> >> > The problem is R5 always using R3 path to reach R1 however the metric
>> >> > of
>> >> > this
>> >> > path is higher than the one coming from R4, Any Idea, Thanks
>> >> >
>> >> >
>> >> > Best Regards;
>> >> >
>> >> > M.Kamar
>> >> >
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>> >> Ronald Angello
>> >> Network Architect
>> >> CCIE 17846
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>> Ronald Angello
>> Network Architect
>> CCIE 17846
>> CCDP, CCIP, CCNP
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