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Forum Replies

  1. sims says:

    Hi,

    I was trying the lab on gns3 and the image is cisco IOSv ,

    Why cost is 1000 here , it should be 10 right ?

    interface GigabitEthernet0/0
     bandwidth 100
     ip address 192.168.12.2 255.255.255.0
     duplex auto
     speed auto
     media-type rj45
    end

    -

    spade#sh ip ospf interface gi0/0
    GigabitEthernet0/0 is up, line protocol is up
      Internet Address 192.168.12.2/24, Area 0, Attached via Network Statement
      Process ID 10, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 1000

    Thanks

  2. Thank you so much for your answer and patience.

    I already did what you told me for static routes and I will do the same to redistribute BGP prefix list to OSPF.

    If I already have BGP filters (prefix-list) can I use the same prefix-lilst to create a route-map to filter the networks announce by BGP to OSPF?

    example

    router bgp 65533
     neighbor 6.6.6.6  remote-as 65533
     neighbor 6.6.6.6 update-source Loopback0
     neighbor 6.6.6.6 prefix-list PRUEBA in
    
    ip prefix-list PRUEBA permit ip 10.250.20.0/24   --> ( I have a lot of prefix list for filtering but that is for that example)
    
    
    route-map BGP-TO-OSPF permit 10
    match ip address prefix-list PRUEBA
    
    
    router ospf 1
    redistribute BGP 64518 route-map BGP-TO-OSPF

    Thank you so much for your answer.

  3. Great Web Lesson Rene!

    Word of advice buy Rene book on CCNP Route. Study the chapters such as I read all of the OSPF chapters through twice. Then I come to the web pages which I buy a year subscription to at a time as its a little cost savings.

    On the web pages especially one like this where Rene has video its great to watch those as added reinforcement.

    For example, First video Rene is talking about all the areas and how OSPF works. he shows you a ABR and ASBR. When he is doing this if you have studied the book first you are seeing LSA type 3 summary network LSA so it knows where to find the ABR. Then when he mentioned the ASBR I was thinking and oh yah there is a type 4 LSA so it can find the ASBR, and finally that linked into him giving example of Redistributed route and there I though oh yah there will be a LSA type 5 for redistribution and all these things link together so even when he may not mention it in the video because that video is explain something slightly different but related you think about it in your head and see it because you have studied the CCNP Route book first.

    On the another video same lesson he talks about what is contained in a hello packet its small thing but he mentions when talking about DR and BDR that routers have a default priority but if you read through he book first you know that is default of 1 and that leads your brain down related stories such as don’t want something to become DR or BDR then choose 0 or if you want it to be something else he specifically mentions in the video as he did in book you can increase the priority.

    So each thought about something leads you to things related to that thought. While the material Is also covered in-depth on these web pages its slightly different and the videos are sound instead of visual so another type as well.

    I am telling you this really reinforces the information so buy the book read it get basic understanding and then study the web lessons it will cement the knowledge or at least it does for me!

    Thanks Rene for a great lesson!

  4. Hello Rene,
    I did a packet capture and was studying Hello packet in ospf.
    My setup here is like this R1------------------------------R2
    192.1681.1.1 192.168.1.2
    I enabled OSPF on R2 first so it started sending Hello packet, then next I configured OSPF on R1 so now R1 also started sending hello packet. Now as soon as R2 got the hello from R1 then it did an ARP saying who is 192.168.1.1 tell 192.168.1.2. So why this ARP happens at first place and I see this ARP happening on R2 only not on R1, my second question.
    I am also attaching the packet capture.hello.pcapng (13.0 KB)

  5. Hello Ravi

    This is an excellent question, it shows that you are thinking analytically and very deeply about these issues.

    When a router sends an OSPF hello packet, it sends it to the 224.0.0.5 multicast address. When R2 receives this packet, one of the pieces of information it receives in the OSPF header is the IP address of the router that sent it.

    Now the next step to establishing a neighbour adjacency is for R2 to respond with a unicast packet sending its router ID and its neighbour list. However, in order to do this, it must encapsulate the response, which is an IP packet, into a frame. In order to do that, it must learn the destination MAC address, something it does not yet have in its ARP table since the initial communication was a multicast packet. So it initiates an ARP request for the IP address of R1 and receives the MAC address. It can then further encapsulate the frame and send it on its way.

    I hope this has been helpful!

    Laz

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