Re: preferring OSPF inter-area compared to intra-area

Marc,
   It's good when you know how something works and can think through a
problem like you just did as opposed to not knowing how something works
and having to look at command outputs to try and figure out what happened.
 You're working on a different level when you know the outcome before
putting a configuration in. Unfortunately some people never get to this
level.

Brian Dennis, CCIEx5 #2210 (R&S/ISP-Dial/Security/SP/Voice)
bdennis_at_ine.com

INE, Inc.
http://www.INE.com

On 1/9/13 2:16 AM, "marc edwards" <renorider_at_gmail.com> wrote:

>No need to lab it. I understand that no inter area route exists to be
>installed in global. Was good discussion when blocking out the noise.
>Thanks
>
>Marc
>
>On Tuesday, January 8, 2013, marc edwards wrote:
>
>> Sorry, Brian. I should lab this up instead of just asking. Sometimes
>> you guys make it too simple ;)
>>
>> cheers,
>>
>> Marc
>>
>> On Tue, Jan 8, 2013 at 8:39 PM, marc edwards
>><renorider_at_gmail.com<javascript:;>>
>> wrote:
>> > So what would happend if the Inter area route was set to lower
>>distance?
>> >
>> > On Tue, Jan 8, 2013 at 3:45 PM, Brian McGahan
>><bmcgahan_at_ine.com<javascript:;>>
>> wrote:
>> >> You can use distance to filter, but you can't use it to prefer one
>> route type over another. If you have an Intra-Area route and an
>>Inter-Area
>> route for the same prefix, the Intra-Area route is chosen as best and
>>goes
>> to the OSPF RIB. The distance is then applied to the OSPF RIB before
>>the
>> route goes to the global RIB, which is the routing table. The issue
>> becomes that even if you poison the Intra-Area route by setting its
>> distance to 255, it was the only route in the OSPF RIB to begin with,
>>and
>> the end result is that OSPF feeds no route to the RIB for that prefix.
>> >>
>> >> In other words you can deny OSPF from installing the prefix in the
>> routing table overall, but you can't deny it from installing the
>>Intra-Area
>> route in order to get it to install the Inter-Area route instead.
>> >>
>> >> This is the same type of reason that Sham Links are implemented in
>>MPLS
>> L3VPN with OSPF as the PE-CE routing protocol, because if you're
>>migrating
>> off of a private layer 2 VPN service like Frame Relay to MPLS L3VPN,
>>your
>> Intra-Area routes over the Frame Relay network would always be preferred
>> over the Inter-Area or External routes coming from the MPLS L3VPN. The
>>fix
>> is to run a Sham Link over the MPLS L3VPN which makes the routes be
>>able to
>> come in as Intra-Area. If you now have an Intra-Area route over Frame
>> Relay and an Intra-Area route over MPLS you can just change the link
>>costs
>> so that the Frame Relay is used as a backup.
>> >>
>> >>
>> >>
>> >> Brian McGahan, CCIE #8593 (R&S/SP/Security)
>> >> bmcgahan_at_INE.com
>> >>
>> >> Internetwork Expert, Inc.
>> >> http://www.INE.com
>> >>
>> >>
>> >> -----Original Message-----
>> >> From: marc edwards [mailto:renorider_at_gmail.com <javascript:;>]
>> >> Sent: Tuesday, January 08, 2013 4:45 PM
>> >> To: ccie99999
>> >> Cc: rakesh madupu; Jay McMickle; Brian McGahan; Narbik Kocharians;
>> Carlos G Mendioroz; Cisco certification
>> >> Subject: Re: preferring OSPF inter-area compared to intra-area
>> >>
>> >> Try using distance command under ospf process of R6 to manipulate
>>path
>> selection. I am surprised this wasn't suggested..... or did i miss it?
>> >>
>> >> Why don't you try using distance command under ospf process
>> >>
>> >> On Tue, Jan 8, 2013 at 12:19 PM, ccie99999
>><ccie99999_at_gmail.com<javascript:;>>
>> wrote:
>> >>> Hi Rakesh,
>> >>>
>> >>> yeah.. I'm just filtering rib and not ospf db.
>> >>> I've no idea of I could make an inter-area route become an
>>intra-area,
>> >>> using a route-map or a filter.
>> >>> Best way is move the interface to the same area or use a VL I need
>>to
>> >>> lab it a bit.
>> >>>
>> >>> On Tue, Jan 8, 2013 at 5:19 PM, rakesh madupu
>><raaki.88_at_gmail.com<javascript:;>>
>> wrote:
>> >>>
>> >>>> Rakesh
>> >>>
>> >>>
>> >>>
>> >>>
>> >>> --
>> >>> @ccie99999
>> >>> https://twitter.com/ccie99999
>> >>>
>> >>>
>> >>> Blogs and organic groups at http://www.ccie.net
>> >>>
>> >>>
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Received on Wed Jan 09 2013 - 18:02:23 ART