OSPF Auto Cost Reference Bandwidth


The new muppet movie is almost finished. All the actresses prefer to have a dedicated internet connection in their trailers at the movie park. You configure a couple of routers with Gigabit and FastEthernet interfaces. Unfortunately OSPF doesn’t seem to make a difference between FastEthernet and Gigabit links. It’s up to you to make the changes so it does see a difference…


  • All IP addresses have been preconfigured for you.
  • Configure OSPF on all routers. Achieve full connectivity.
  • Without changing the OSPF cost on each interface, ensure OSPF will make the best use of the Gigabit interfaces. In the future you will also add some ten Gigabit links so this is something to be aware of.

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OSPF Auto-Cost Reference Bandwidth Network Topology

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Written by René Molenaar - CCIE #41726

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About the Author: Rene Molenaar

René - CCIE #41726 is the creator of GNS3Vault.com where he shares CCNA, CCNP and CCIE R&S labs. He also blogs about networking on http://networklessons.com


  1. do we simply set the reference bw to 10000 Mbps? this set’s it at 10Gbps correct, as the bw is defined as Mbps.

  2. Yup that’s it. By default OSPF will use a 100mbit interface for the reference bandwidth. That means a 100mbit interfaces gets a cost of 1. (100 / 100 = 1).

    You can’t have a cost of 0,1 for Gigabit or 0,01 for 10Gigabit. That’s why you need to change the reference bandwidth.

    If you get it to 10Gigabit then it’ll look like this:

    10Gigabit: Cost 1
    Gigabit: Cost 10
    100Mbit: Cost 100

  3. when you download this config

    check salena configs. the interface configure wrong.
    and one interface not even configured.

  4. hi ! i can’t find giga ethernet link in gns “add a link “option ,i also tried from router right click configure slot tap but it wasn’t found , can anyone help me on this ?

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