OSPF Areas

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Jul 16th, 2008
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I using 2 seperate router for 2 external connection and this is connected to one router which is connected to my LAN using firewall. The external link is MPLS and i am using OSPF.The first external connecting is configured as area 0 and second is area 1. Now my question is;

Will both the routers will pass route if a single process ID is used in the router which is connected to LAN.

How can i do a routing by make both areas as stand alone to each other.

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lee.reade Wed, 07/16/2008 - 01:13
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Its not clear what you are trying to do from your description.

Are you saying that you will have one CE router with a link to two PE routers that then connect to the MPLS core?

Are you wanting to have one ospf database for traffic from one PE and another separate ospf database for the other PE?

PE------mpls core


PE------ mpls core

Is this what you are descibing??


drnteam Wed, 07/16/2008 - 01:35
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Yes, I have one CE router and two PE router. And I need seperate database for each link on CE router.

lee.reade Wed, 07/16/2008 - 01:37
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What are you trying to achieve with this ?


drnteam Wed, 07/16/2008 - 01:56
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The reason of seperated database is they both belongs to 2 higly secured area and i dont want this network to communicate with each other. How can i resctict one link to pass the routes to other. Is it good to have 2 seperated process ID.

lee.reade Wed, 07/16/2008 - 02:04
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If you are looking at separating the traffic from each other securely, then you could use VRF LITE.

This would place each interface facing the PE into its own VRF, so it would have its own routing table.

But using this approach means that you would need to use VRF LITE throughout your internal network aswell, which may be too much work for you.

Its kinda hard to advise on this, since we dont know how the internal network is setup. How are you keeping them apart when in your internal network?

If you are usng 802.1q for this, then perhaps your best bet would be to use a separate CE for each connection.

PS. I assume that the PE is providing two different VRFs, one for each CE, or are they in the same VRF?



Kevin Dorrell Wed, 07/16/2008 - 02:01
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I'm not sure I understand entirely what you are trying to achieve, but I would make your external links two seperate areas (as they are at the moment), but non-zero (e.g. 1 and 2). I would then have a backbone area (area 0) that connects the central router and your two external routers (and perhaps your firewall). In this case, your two external routers are ABRs.

Alternatively, you could put the links between your hub router and the external routers into the areas 1 and 2, and create a dummy area 0 on your hub router consisting of a loopback interface. Do you run OSPF between your firewall and the hub router? If so, that link would be area 0.

Either way, you can use inter-area filtering or area-range summarisations to determine how much information passes between your two external areas.

Kevin Dorrell



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