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Confusion with OSPF over NBMA (frame)

Jul 4, 2010 4:25 PM

ben 24 posts since
Oct 14, 2008

I KNOW there is some concept here I am not grasping having played with this multiple times with the same result so here goes...

 

I have a full mesh network with 4 routers (say R1, 2, 3, and 4)

 

All routers are connected to eachother with PVCs using INARP.

R1 will be the hub and will be configured with a defaule priority of 1 while all other routers are configured with a priority of 0.

 

Now I've set up neighborships with the the neighbor command for all routers to R1 (the hub) and everythings good.

The problem starts when I want to setup neighbors with other routers and heres what happens:

 

If I go on R4 and enter the neighbor command to map it to R3 the neighbor gets stuck in attemp with N/A under router ID.

Weirder still if I terminal into R3 and do a show ip ospf neighbors I see R4 int the INIT state! With R4 ID listed.

 

Is there something I'm not getting?

  • Ryan Ruckley CCNP 378 posts since
    Aug 26, 2009
    Currently Being Moderated
    1. Jul 4, 2010 4:43 PM (in response to ben)
    Re: Confusion with OSPF over NBMA (frame)

    Ben,

     

    You need to look into OSPF network types a little more. The default network type for frame when not point-to-point is nonbroadcast. This means there will be a DR/BDR elected but no dynamic discovery of neighbours. So far so good, you've disabled DR election for your hub routers but I have a strange feeling they can only be a neighbour with the DR if they are not participating in the election process.

     

    To be honest, if you're going for a hub and spoke design why not use point-to-multipoint as your network type, or seeing as though you have a full mesh, use broadcast as your network type. If you want to manually configure neighbours you can use point-to-multipoint nonbroadcast.

     

    Others may have a better idea of why what you are attempting doesn't work but from a design point it doesn't make sense with a full mesh.

     

    If you wish to simulate a partial mesh you can disable inarp and do static mapping.

     

    Any help?

  • Ryan Ruckley CCNP 378 posts since
    Aug 26, 2009
    Currently Being Moderated
    3. Jul 4, 2010 5:42 PM (in response to ben)
    Re: Confusion with OSPF over NBMA (frame)

    Sorry for the very vague statment, you would think, having just passed my ROUTE exam that this stuff would still be fresh.

     

    For a proper neighbourship to form, each statically defined neighbour must see itself in hello's recieved from the other neighbours.

     

    Check here

     

    Also check to see if your dynamic frame relay maps include broadcasts, I presume they do as you have a proper relationship with the DR.

     

    "Two-way: There is bi-directional communication with           a neighbor. The router has seen itself in the Hello packets coming from a           neighbor. At the end of this stage the DR and BDR election would have been           done. At the end of the 2way stage, routers will decide whether to proceed in           building an adjacency or not. The decision is based on whether one of the           routers is a DR or BDR or the link is a point-to-point or a virtual           link."

     

    Perhaps for some reason the neighbour statements are sending the wrong details so that the recieved hello's don't contain the right router id?

     

    You could do a debug ip ospf adj to see if there is anything it is complaining about.

  • Ryan Ruckley CCNP 378 posts since
    Aug 26, 2009
    Currently Being Moderated
    5. Jul 6, 2010 12:03 AM (in response to ben)
    Re: Confusion with OSPF over NBMA (frame)

    Ben,

     

    I would guess that the hellos are getting from R1 to R2 but are being rejected by R2?

     

    Also I note that R1 has a state of ATTEMPT which according to my TSHOOT book is after a router sends a unicast hello which would make sense if you had statically defined your neighbours.

     

    Going back to your original post:

    • statically defining a neighbour only on one side would result in that side sending a unicast hello to the defined neighbour.
    • The sending neighbour would go to the ATTEMPT state (so far so good)
    • The receiving neighbour would go to the INIT state upon receving the hello (so far so good)
    • At this point the receiving neighbour does not respond.

     

    So what you are seeing in the neighbour states matches exactly with the receiving neighbour not responding to a unicast hello.

     

    So:

    Do you have a symetric neighbour statement on both ends?

    Is your network type set to require static neighbours? e.g. nonbroadcast

    Does all your neighbour criteria match? Hello timer, Dead timer, Area, Area type, subnet (including mask) and authentication?

    Does the neighbourship work when you change the network type to something that does dynamic neighbour discovery (broadcast/point-to-multipoint)?

     

    That's all that I can think of right now.

     

    Any progress?

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    6. Jul 6, 2010 1:52 AM (in response to Ryan Ruckley CCNP)
    Re: Confusion with OSPF over NBMA (frame)

    Ben,

     

    Ryan has given you a good start point in his last post.  In addition, please verify the neighbor relationships on all routers with the "sh ip ospf nei" command.  You mention you have connection with all routers via PVC except R2 and R10.  However, in the outputs you provided it shows that even R1 and R2 are not connecting.  I suspect because the priority on R1 = R2 = R10 = 0, you will not be able to form neighbor adjacencies between these routers.  They will only be able to form neighbor adjacencies with R7 (DR) and R9 (BDR).  I see from the output it looks as though you have a single subnet for all routers 10.100.100.0/24, with the router number equal to the last octet.  Can you post some configs (text files) for each router.  This may help us understand exactly wehat is going on.

     

    I will lab this up when I get to work and see what I get.

     

    HTH

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    8. Jul 6, 2010 1:53 PM (in response to ben)
    Re: Confusion with OSPF over NBMA (frame)

    Ben & Ryan,

     

    I suspect the priority may be a problem.  Reason behind my thoughts, the default network type for OSPF is NBMA, and you have a DR/BDR selection.  Which means all routers for adjacencies with the DR/BDR.  However, you were trying to form an adjacency between two DROTHERS, which may not be possible.  I still would like to see some configs of atleast the serial interfaces and ospf for each router.  I did lab this up at work last (simulator) and I had nop problem bringing up the FR network (did that first)  The config on the serial interface where very basic.

     

    int s0

    ip add 192.168.1.1 255.255.255.0

    encap frame-relay

     

    this was on all routers ( note IP add were .1, .2, .3, .4, and .5 all /24 prefix)

     

    The default for the FR links on physical interface (no subinterfaces used) is Cisco's proprietary P2M (broadcast).  This can be seen in the output of the "sh frame-relay map" command.  Inverse-ARP is enabled by default, and all PVCs will come up.  I could ping from R1 to all other routers serial interface.

     

    When I enabled OSPF, I only had neighbor adjacency between R4 (BDR) and R5 (DR), due to the Router-Id R4 = 4.4.4.4 and R5 = 5.5.5.5.  The others would not form.  In my simulator I am limited on the debug commands, so could not look deeper into this.  Remember with OSPF over NBMA, you need to fix either with the "neighbor" command under the OSPF routing process or use "ip ospf network point-to-mulipoint" under the serial interfaces.  Again my simulator would not take the neighbor commands (this is being phased out in favor of the ospf network commands).  When I put the "ip ospf network point-to-multipoint" command under the interfaces all was good.  When you do this there will be no DR/BDR selection, and all adjacencies will form to "FULL" state.  I am at home now, but will post the configs when I get back to work tonight.  The network type for the interface should change to P2M.  Can be verified with the "sh ip ospf int s0" command.  My simulator still showed them as P2P (default for serial ports).

     

    Again, your router configs would really help.  I created a little frame-relay network with five routers (R1 - R5), but I want to make sure I set up my frame-relay network the way you did, or at least as close to what you have.

     

    Look forward to your replies.

     

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    11. Jul 6, 2010 10:25 PM (in response to ben)
    Re: Confusion with OSPF over NBMA (frame)

    Thanks Ben, I will take a closer look when I get to work in the next couple of hours.  I did notice that R7 is empty (no file).  Also, can you provide a quick connection map R1 S0/3 to FRS x/x and so forth.  This will make it easier than trying to go through all the mappings to see which router connects to which port on the FRS.  Thanks.

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    12. Jul 7, 2010 4:54 AM (in response to Brian)
    Re: Confusion with OSPF over NBMA (frame)

    Aloha Ben,

     

    I went through the configs and well had a little trouble identifying which DLCIs you were using for connection to each of the routers as some numbers were used more than once.  In addition, I noticed you did not have all the DLCIs set up for full mesh capability.   So, I created a little DLCI matrix for you.  Use the following DLCI matrix below for your configs.  Make sure that layer 2 (Frame Relay) comes up first.  Then enable OSPF.  The changes needed for each router can be found below as well.

     

    From / ToR1R2R7R9R10

    R1

    102103104105
    R2201203204205
    R7301302304305
    R9401402403405
    R10501502503504

     

    ===========================================
    **Use if inverse-ARP is enabled**
    ===========================================

    R1
    frame-relay interface-dlci 102
    frame-relay interface-dlci 103
    frame-relay interface-dlci 104
    frame-relay interface-dlci 105

     

    R2
    frame-relay interface-dlci 201
    frame-relay interface-dlci 203
    frame-relay interface-dlci 204
    frame-relay interface-dlci 205

     

    R7
    frame-relay interface-dlci 301
    frame-relay interface-dlci 302
    frame-relay interface-dlci 304
    frame-relay interface-dlci 305

     

    R9
    frame-relay interface-dlci 401
    frame-relay interface-dlci 402
    frame-relay interface-dlci 403
    frame-relay interface-dlci 405

     

    R10
    frame-relay interface-dlci 501
    frame-relay interface-dlci 502
    frame-relay interface-dlci 503
    frame-relay interface-dlci 504

     

    FRS
    interface s0/0
    description CONNECTION TO R7
    frame-relay route 301 interface serial0/1 103
    frame-relay route 302 interface serial0/2 203
    frame-relay route 304 interface serial0/3 403
    frame-relay route 305 interface serial1/0 503

     

    interface s0/1
    description CONNECTION TO R1
    frame-relay route 102 interface serial0/2 201
    frame-relay route 103 interface serial0/0 301
    frame-relay route 104 interface serial0/3 401
    frame-relay route 105 interface serial1/0 501

     

    interface s0/2
    description CONNECTION TO R2
    frame-relay route 201 interface serial0/1 102
    frame-relay route 203 interface serial0/0 302
    frame-relay route 204 interface serial0/3 402
    frame-relay route 205 interface serial1/0 502

     

    interface s0/3
    description CONNECTION TO R9
    frame-relay route 401 interface serial0/1 104
    frame-relay route 402 interface serial0/2 204
    frame-relay route 403 interface serial0/0 304
    frame-relay route 405 interface serial1/0 504

     

    interface s1/0
    description CONNECTION TO R10
    frame-relay route 501 interface serial0/1 105
    frame-relay route 502 interface serial0/2 205
    frame-relay route 503 interface serial0/0 305
    frame-relay route 504 interface serial0/3 405
    =============================================
    =============================================
    **If inverse-ARP is disabled you need to use the frame-relay map command.  Also, you need to change the ospf network type with the ip ospf network command.  Below is an alternate configuration for the routers.  The FR switch config stays the same as above.

     

    R1
    ip ospf network broadcast
    frame-relay map ip 10.100.100.2 102 broadcast
    frame-relay map ip 10.100.100.7 103 broadcast
    frame-relay map ip 10.100.100.9 104 broadcast
    frame-relay map ip 10.100.100.10 105 broadcast

     

    R2
    ip ospf network broadcast
    frame-relay map ip 10.100.100.1 201 broadcast
    frame-relay map ip 10.100.100.7 203 broadcast
    frame-relay map ip 10.100.100.9 204 broadcast
    frame-relay map ip 10.100.100.10 205 broadcast

     

    R7
    ip ospf network broadcast
    frame-relay map ip 10.100.100.1 301 broadcast
    frame-relay map ip 10.100.100.2 302 broadcast
    frame-relay map ip 10.100.100.9 304 broadcast
    frame-relay map ip 10.100.100.10 305 broadcast

     

    R9
    ip ospf network broadcast
    frame-relay map ip 10.100.100.1 401 broadcast
    frame-relay map ip 10.100.100.2 402 broadcast
    frame-relay map ip 10.100.100.7 403 broadcast
    frame-relay map ip 10.100.100.10 405 broadcast

     

    R10
    ip ospf network broadcast
    frame-relay map ip 10.100.100.1 501 broadcast
    frame-relay map ip 10.100.100.2 502 broadcast
    frame-relay map ip 10.100.100.7 503 broadcast
    frame-relay map ip 10.100.100.9 504 broadcast

     

    The alternate example above I found while researching OSPF over Frame Relay.
    Many of the documents I came across used the "frame-relay map" command rather than the "frame-relay interface dlci" command.  Here are a few of those links:

     

    Running OSPF in NBMA and Broadcast mode over Frame Relay
    http://conft.com/en/US/tech/tk365/technologies_tech_note09186a0080094051.shtml

     

    OSPF over Frame Relay subinterfaces
    http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094054.shtml

     

    RFC on running OSPF over Frame Relay Networks
    http://www.rfc-editor.org/rfc/rfc1586.txt

     

    HTH

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