Re: OSPF default route multiple processes

Hi Chris,

We were migrating from EIGRP to OSPF in our new data center network (now
area 0), and from static to OSPF in our old data center network (now area
51). As the old network is on its way to be phased out and holds some very
delicate production systems we wanted to keep them completely separated (so
we could make changes in the one without affecting the other) yet both on
OSPF for simplicity. Since both have their own Internet exit(s) we needed
to do some filtering back and forth.

I think what I am going to do is lower the distance of area 51 so the
default route will be preferred of area 51.

Cheers,
Marc

On Sat, Jul 27, 2013 at 2:51 PM, Chris Rae <chris.rae07_at_me.com> wrote:

> Can I ask a question.
> What was the design reason for using multiple instances of the OSPF
> process?
>
>
> Chris
>
> On 27/07/2013, at 5:26 AM, Marc La Porte <marc.a.laporte_at_gmail.com> wrote:
>
> > Thanks, Jose...
> >
> > On Fri, Jul 26, 2013 at 9:10 PM, Jose Zamora <joszompr_at_gmail.com> wrote:
> >
> >> In this case both OSPF process are treated as different routing
> protocol
> >> instances so the router is going to compare de AD of both to select the
> >> best route, in case of a tie like in this escenario its going to select
> the
> >> one learned first.
> >>
> >> Because of this it could work like you expect for a while but a
> >> convergence on the network could change the behavior.
> >>
> >> You could change the AD of one of the process to force it to use the
> >> default you want
> >>
> >> Regards
> >>
> >> Jose
> >>
> >>
> >> On Fri, Jul 26, 2013 at 11:24 AM, Kristian Francisco <
> >> kristian.j.f_at_gmail.com> wrote:
> >>
> >>> Hey Marc, I would like to take a stab at your questions, but will let
> some
> >>> of the CCIEs with more experience confirm. I would expect the
> following to
> >>> take place:
> >>>
> >>> Although there are two ospf processes running, there's only one routing
> >>> table. I would not expect ospf to treat its rules on route selection
> >>> differently. (this is an assumption). For true segmentation, consider
> >>> vrfs.
> >>>
> >>> As you mentioned, the type-1 LSA to be preferred over a type-2 LSA.
> Once
> >>> you make the default routes both of the same type, the following
> selection
> >>> criteria will apply:
> >>>
> >>> - If type-2 metric is the same, prefer route with better internal
> cost.
> >>> - Directly from RFC: In any case, among the remaining routing table
> >>>
> >>> entries, select the routing table entry with the least cost; when
> >>> there are
> >>> multiple least cost routing table entries the entry whose associated
> >>> area
> >>> has the largest OSPF Area ID (when considered as an unsigned 32-bit
> >>> integer) is chosen.
> >>>
> >>> Best Regards,
> >>>
> >>> Kristian J. Francisco
> >>>
> >>>
> >>> On Fri, Jul 26, 2013 at 10:20 AM, Marc La Porte <
> marc.a.laporte_at_gmail.com
> >>>> wrote:
> >>>
> >>>> Rati,
> >>>>
> >>>> How does it choose between the two processes though?
> >>>>
> >>>> Cheers,
> >>>> Marc
> >>>>
> >>>> On Fri, Jul 26, 2013 at 7:12 PM, Rati Berikaant Jokhadze
> >>>> <iinfo83_at_gmail.com>wrote:
> >>>>
> >>>>>
> >>>>> On 07/26/2013 08:50 PM, Marc La Porte wrote:
> >>>>>
> >>>>>> 1. What is the order of operation within OSPF to select default
> >>> routes
> >>>>>> from
> >>>>>> different processes?
> >>>>>>
> >>>>>> 2. How do I ensure the border router ALWAYS takes the default route
> >>> from
> >>>>>> Area 51 (although it has multiple default routes from Area 0 in it's
> >>>>>> database)? Since OSPF metric-type 1 has preference over metric-type
> >>> 2,
> >>>> do
> >>>>>> I
> >>>>>> change the metric-type in Area 51 to type 2 and ensure it's always
> >>> lower
> >>>>>> than from Area 0?
> >>>>> 1. First recieved route within process
> >>>>>
> >>>>> 2. I dont think so , that you can do this , someone will answer
> >>>> exactly...
> >>>>
> >>>>
> >>>> Blogs and organic groups at http://www.ccie.net
> >>>>
> >>>>
> _______________________________________________________________________
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> >>>
> >>>
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> >>>
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> >>
> >>
> >> --
> >> Atentamente Jose Zamora Prado
> >> Telefono 8252885
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
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Received on Sat Jul 27 2013 - 17:33:44 ART