Re: OSPF default route multiple processes

Hi Mark

INE have a great blog by the one and only Brian which is really the level you need to understand the metrics in path selection for E2 also the decision taken to LSA 5's

http://blog.ine.com/2011/04/04/understanding-ospf-external-route-path-selection/

When redistributing between mutual OSPF processes, then please read Cisco's guide here and watch for sub-optimal routing, this of course depends if the redistribution is between two OSPF routers on a shared segment.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00801069aa.shtml

--
BR
Tony
Sent from my iPad
On 26 Jul 2013, at 17:50, Marc La Porte <marc.a.laporte_at_gmail.com> wrote:
> Hi all,
> 
> I have a situation within our data center where I have two OSPF processes
> (each with only one area) and a single point of contact (border router)
> between the two. I have OSPF process 51, area 51; and I have OSPF process 1
> area 0.
> 
> Area 51  has a single Internet connection and the point where I do a
> default-information originate (type 2; default metric)
> Area 0 has two Internet connections and both do a default-information
> originate (type 1; different metrics)
> On the border router, there is mutual redistribution of all routes except
> the default route which is filtered out in both directions (so each area
> has it's own Internet exit)
> The border router MUST take the default route from Area 51 always.
> 
> Well, I got this whole setup working stable for months now until last
> Tuesday. And there's a default router on the border router from area 0,
> while the Area 51 has the better metric (1) versus metric 10 and 20 from
> Area 0.
> 
> QUESTIONS:
> 
> 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?
> 
> 
> Looking forward hearing from you.
> 
> If you need more info, please let me know.
> 
> (Brian, I couldn't find any blogs on INE about OSPF multiple processes. Is
> this an idea for a future blog post maybe?)
> 
> Cheers,
> Marc
> 
> 
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