Re: OSPF Path selection question

Hi Mohamed,
from a design perspective, why do you need more than one area? Do you have a
lot of router in area 0, connected to R4 and R5?

If so, what about put link R4<->R5 in area1 instead of area0?

-mirco.

On Mon, Mar 22, 2010 at 1:14 AM, mohamed kamar <mohamed_kamar_at_hotmail.com>wrote:

> Thanks Ronnie for your help;
>
>
>
> I think i'll go for installing a new Area 1 link between R4 and R5 to
> force
> the traffic to take this path, Thanks a gain for your help
>
>
>
> Best Regards;
>
> Mohamed Kamar
>
> > Date: Sun, 21 Mar 2010 11:13:21 -0400
> > Subject: Re: OSPF Path selection question
> > From: ronnie.angello_at_gmail.com
> > To: mohamed_kamar_at_hotmail.com
> > CC: ccielab_at_groupstudy.com
> >
> > 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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> > >> >> >
> > >> >>
> > >> >>
> > >> >>
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Received on Mon Mar 22 2010 - 17:56:54 ART