RE: OSPF Path selection question

Hi Mirco;

  The reasons of having multiple areas is that each area connected to one
provider, And some sort of filters and summarization are required, going back
to the problem, yes the solution i conclude from your conversation and other
conversations is there is no way to change this OSPF behavior and the work
around is either put area 1 link between R4 and R5 or create a tunnel between
them to force the traffic to take this path, Thanks

Best Regards;

   Mohamed Kamar

> Date: Mon, 22 Mar 2010 17:56:54 +0100
> Subject: Re: OSPF Path selection question
> From: mirco.orlandi_at_gmail.com
> To: mohamed_kamar_at_hotmail.com
> CC: ronnie.angello_at_gmail.com; ccielab_at_groupstudy.com
>
> 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
> > > >> >> >
> > > >> >> >
Received on Tue Mar 23 2010 - 08:29:56 ART