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  • OSPF Topology

    I'm trying to figure why my routing topology isn't work as it should. I need to make an project for some dwdm equipments to be managed from one central location. Because the project contains more than 100 devices I split the map into 3 different OSPF areas. The problem with this topology is that is very unstable. If one of the optical devices is down, in many cases, just one backbone router of total of five "hear" about this change. The backbone routers are distributed along the borders of transit areas. To be more clear I'll attach a small picture which contains only 2 backbone routers. In the picture, I draw 2 routers, both have physical connections to Area 1 and 2 and the direct link between this two is defined as a trunk, for carrying 2 vlans : one for area 2 protection and another for backbone connectivity. Each one of this vlans has IPs from different subnets and they are assigned on different logical interfaces. Did someone tried a topology like this : to carry 2 different logical links which are in different areas over the same wire? In a lot of documentations I saw that is necessary to have an interface only in one area but I think there is no difference between physical and virtual ones. Am I wrong? Any advise can be useful. Thanks in advance and excuse my bad English.
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  • #2
    Re: OSPF Topology

    It's extremely difficult to determine your problem based on the two router drawing. I don't see why you would ever want an interface in more than one area. You can have as many transient links as your want crossing one physical path, so that's not your issue. Where's area 0?

    If you can provide a better drawing, this may make alot more sense. I doubt this is helping you, so sorry.
    -Tim

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    • #3
      Re: OSPF Topology

      Unfortunately, the topology is moreeee complex than this draw, and in this moment i'm not at work to make a scan from the paper.
      The backbone area (Area0) is carried only by the 10Mbps link that interconnects all 5 backbone routers (in my drawing I figure just 2 of those routers because the arrangement repeats for all of them). Because of arrangement of dwdm devices and because I don't want them to be part of backbone area this is the only solution that I found : area 0 looks like this : R1 <---->R2<---->R3<---->R4<---->R5. For backbone protection I will use one of optical links, using virtual-link structure.

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      • #4
        Re: OSPF Topology

        ok. so if all your areas are hanging off those 5 routers, every area is connected to an area 0 ABR. correct? you shouldn't even need transient links.

        and this is a little off subject....if you have optical links between your area zero routers, why would they be 10/half? Or am I misinterpreting your explanation?
        -Tim

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        • #5
          Re: OSPF Topology

          The 10Mps links are obtained using some payload in optical links and does not effect the total bandwidth of the optical line and this is the reason for this kind solution. I've start to think that I have made a mistake in the design and the problems that I observed are from that reason (to use one physical link in two different areas). If you think that this design, at least theoretically, must work, I will try read more carefully the ospf database to figure whats wrong.
          By the way : do you know some links for troubleshooting ospf because i'm a beginer in this chapter of routing (some ideas from where should I check the ospf databases etc ). Thanks alot.

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          • #6
            Re: OSPF Topology

            show ip ospf database
            show ip ospf neighbor
            sh ip ospf virtual-link

            To be completely honest, I don't have a clue what this solution you have is, so I don't think I can really help much.

            If your ospf database doesn't contain what you think it should contain start debugging. Start with "debug ip ospf packet" to see what ospf is doing. OSPF debugs are very informative. If you still don't find what your looking for, try debugging one of the other ospf options.


            Your network has point to point connections rather than point-to-multipoint, so link failures should be sent to all neighbors. What state are your devices? They should be FULL/DR, FULL/BDR, or FULL/DROTHER. If this is correct, then you have to find out why LSAs are not being sent out upon link failure detection.

            If you get anything interesting in your debugs post it up.
            -Tim

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            • #7
              Re: OSPF Topology

              All links between optical devices are point-to-point. Unfortunately on those devices debugging ospf is not an alternative : are use a very strange CLI, they call it TL1. On backbone routers I've already checked the adjacencies and every thing looks ok. I've checked the sequence numbers for some LSAs (I can't verify all of them because the ospf database is huge) on all the backbone routers and they are the same; in some cases when one link goes down, even one router has received the same LSA as his neighbors, in the routing table the entry for that dead link still in place.
              About debug commands, is a little bit difficult : the backbone routers are not Cisco, are Nortel, but the operating system is 99% the same as IOS; and the debug commands looks to redirect the messages not into the terminal session but in some file that I didn't managed to see.

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              • #8
                Re: OSPF Topology

                Oh goodness. I'm getting more and more lost. I feel like I'm just asking questions that's wasting your time and not helping in any way.

                Maybe someone else can chime in with something...
                -Tim

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                • #9
                  Re: OSPF Topology

                  Be sure you are not wasting my time. With this kind of explanations we make more clear how this topology looks and maybe someone will have some ideas about what else should I try.

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                  • #10
                    Re: OSPF Topology

                    come on guys, keep it friendly.
                    Cielo, first start with a complete drawing.
                    Marcel
                    Technical Consultant
                    Netherlands
                    http://www.phetios.com
                    http://blog.nessus.nl

                    MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                    "No matter how secure, there is always the human factor."

                    "Enjoy life today, tomorrow may never come."
                    "If you're going through hell, keep going. ~Winston Churchill"

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