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Forum Replies

  1. Hi Rene,

    Can you please explain what is the difference between outside local and outside global IP addresses along with example. Thanks in advance.

  2. Hello Maodo

    Don't worry, you are reading up on CCNA material. Rene is referring to the fact that the Outside Local and the Outside Global addresses are the same. These however can be configured so that they are different. That is, the destination IP address can also be translated by NAT. It is this configuration alone that is outside of the CCNA curriculum. Not to worry, the rest is definitely covered within the CCNA curriculum.

    I hope this has been helpful!


  3. Hello Lazaros,

    Thanks for the explaination.. Can you please explain the use of keywords extendable and reversible in natting with an example.

  4. Thanks for your explanation, Lazaros.

    My question was no so technical. A CCNP lesson telling about CCNA scope ; I thought, it's Copy/Paste error. Now, I understand that one lesson can belong to CCNA and also be re-used, without any change, in CCNP or CCIE courses. I found below the three (CCNA, CCNP, CCIE) links having the same NAT lesson (the lesson that was originally written for CCNA).


  5. Hello Sumit

    There are two types of translation entries: Simple and Extended. A simple translation entry maps one IP address to another. The keyword extendable which indicates an extended translation entry indicates that the translation entry will map an IP address and port pair to another. The extended translation includes the port. An example of such a configuration is the following:

    ip nat inside source static tcp 25 25 extendable
    ip nat inside source static tcp 21 21 extendable
    ip nat inside source static tcp 20 20 extendable
    ip nat inside source static tcp 80 8080 extendable

    Note in the final example that the inside and outside ports do not necessarily have to be the same.

    The reversible keyword according to Cisco "enables outside-to-inside initiated sessions to use route maps for destination-based NAT." This essentially means that a NAT translation entry will be created as soon as the router detects traffic flow from outside to inside using the specific NAT translation. Without this keyword, a NAT entry would only be created when the traffic is sourced from the inside network.

    An example would be the following command:
    Router(config)# ip nat inside source route-map MAP-A pool POOL-A reversible

    This enables outside-to-inside initiated sessions to use route maps for destination-based NAT. Note the reversible keyword is used in conjunction with route maps only.

    I hope this has been helpful!


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