Re: OSPF default route multiple processes

Hey Mark,

Ah, that makes a lot of sense now.
I love the "Area 51'" analogy! ;)

Yeah lowering the AD should do the trick.

Chris

On 27/07/2013, at 11:33 PM, Marc La Porte <marc.a.laporte_at_gmail.com> wrote:

> 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...
>>>>>>
>>>>>>
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>>>>
>>>> --
>>>> Atentamente Jose Zamora Prado
>>>> Telefono 8252885
>>>
>>>
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>
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Received on Sun Jul 28 2013 - 09:52:10 ART