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1354 Views 5 Replies Latest reply: Jan 27, 2011 11:03 AM by Terryk RSS

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NAT and nat pools

Jan 26, 2011 4:49 PM

Terryk 62 posts since
Mar 9, 2010

hello,

 

I am trying to understand the natpool "netmask" .  If I want to use just a part of a subnet for the netpool, would I still use a netmask to cover the entire pool?

 

For example:

 

129.89.32.40 129.89.32.62 netmask 255.255.255.224

 

The subnet would actually go from 33 to 63...  is this okay to use the .224?

 

Are there some rules around the netmask or some suggested appropriate use?

 

I could have missed it, but I am not seeing this question in the ICND2 but perhaps it is covered.

 

Thanks for the information,

  • olliebulle 42 posts since
    Oct 27, 2009
    Currently Being Moderated
    1. Jan 26, 2011 5:05 PM (in response to Terryk)
    Re: NAT and nat pools

    Hi Terryk,

     

    The netmask in the command is used to determine what is the network part and the host part of the range you mention. If you don't mention it, the router doesn't know if the 32 for example in the address is part of the network bits or the host bits. With your mask, we know that these bits are network ones.

  • olliebulle 42 posts since
    Oct 27, 2009
    Currently Being Moderated
    3. Jan 26, 2011 5:49 PM (in response to Terryk)
    Re: NAT and nat pools

    Well, as I understand that, it makes sens the way you type it. The command says : I want to make a NAT pool, with addresses from 129.89.32.40 to 129.89.32.62 and those addresses have the netmask 255.255.255.224, so they belong to the network 129.89.32.32 /27. That doesn't say anywhere to use other addresses than those you mention.

  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    4. Jan 26, 2011 9:11 PM (in response to Terryk)
    Re: NAT and nat pools

    Yes, this is perfectly correct.  the net mask must match the subnet to which the IP addresses in your "pool" belong.  While the entire subnet uses the valid host IP addresses 129.89.32.33 - 129.89.32.62, you are saying I want to use only 40 - 62.

     

    HTH

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