RE: OSPF Path selection question

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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Received on Mon Mar 22 2010 - 00:14:38 ART