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Forum Replies

  1. Rohitendu,
    Cisco has five different options for OSPF over NBMA. Which one you should choose depends on several factors. One important consideration is whether the circuit supports multicast–this will determine whether you must define neighbors manually, or if they can discover each other. Additionally, you need to consider what is the topology of your WAN connection–full mesh, hub and spoke, …? This is important because you must ensure that any router eligible to be a DR or BDR must have reachability to all the other OSPF nodes.

    Here is some information on

    ... Continue reading in our forum

  2. Hi Rene,

    Please help! My topology is simple. R1–FW–R2. I am running ospf between R1 and R2. Firewall between R1 and R2 is transparent. R1 and R2 are able to ping each other through the firewall. However, I keep getting this error message. The hello and dead timer are identical on both R1 and R2. The neighbor already formed. However, it will disconnect and re-form back and forth…

    *Mar  1 03:11:10.743: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/1 from FULL to DOWN, Neighbor Down: Dead timer expired
     --More--
    *Mar  1 03:11:15.243: %OSPF-5-ADJCHG: Proc
    ... Continue reading in our forum

  3. Georgi,
    I think this question would need some clarification, and it depends on whether the two routers are the ONLY routers that are neighbors, or whether there are more than two routers.

    The situation you describe could happen where the router that is in 2-Way has not been elected as a DR or BDR. In this situation (assuming we are dealing with a multi-access network), this is perfectly normal to have a 2-Way state. Any router that is not a DR or BDR that has a neighbor relationship with another router that is also not a DR or BDR would show up as 2-Way/DROTH

    ... Continue reading in our forum

  4. Hi Networklesson team ,

    I was searching for a issue that “why ospf neighbors will stuck at exstart/exchange state” , i got good explanation at below cisco link .

    https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13684-12.html

    please note at step 5 :
    ____________________________________________________________________________________
    Router 7 debug output:

    ***OSPF ENABLED ON ROUTER7, BEGINS SENDING 
    HELLOS AND BUILDING A ROUTER LSA  ////please note router building LSA Type 1////
    00:17:44: IP: s=170.170.11.7 (local), d=224.0.0.5 
    (Seria
    ... Continue reading in our forum

  5. Hi Sameer,

    I have a detailed explanation of the OSPF neighbor adjacency here:

    https://networklessons.com/ospf/ospf-packets-and-neighbor-discovery/

    In the LOADING state, LSUs are exchanged and when that’s done, the routers will show that they are synchronized. Once that’s done, they have everything they need to run SPF.

    You can see the adjacency and SPF in action (and in the right order) if you enable these two debugs:

    debug ip ospf adj
    debug ip ospf spf statistic
    

    Try that next time you have two routers, it’s interesting to see.

    Hope this helps!

    Rene

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