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Routing private IPs

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Oct 13th, 2005
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I am hearing conflicting stories and I need some opinions. Is it possible/proper to route private IPs? Is it proper to use public ips in a network using NAT to get to the internet?

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thisisshanky Thu, 10/13/2005 - 07:23
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You cannot route private IPs on the internet. You will have to NAT to a public address to get access to the internet.

Richard Burts Thu, 10/13/2005 - 07:29
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I am not sure that I understand fully what you are trying to get at. When you mention private IPs am I correct that you are talking about the RFC1918 addresses (,, and It is certainly possible and proper to route these addresses within your own network. It is problematic trying to route these outside of your own network. If you send routing updates outside of your own network you should not be advertising these networks to other public networks.

I am not sure about the last part of your question where it talks about using NAT to get to the Internet. I have a customer who has a class B address space which they use on their internal network. They do NAT all of their traffic going to the Internet. I think that is entirely proper.

If these do not address your question adequately then perhaps you can clarify your question for us.



wrwiii122 Thu, 10/13/2005 - 11:45
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Yes question answered. How about if I use public addresses on a network but then use natting. Is that legal?

readamson Thu, 10/13/2005 - 18:12
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Yes, this is certainly "legal". You can NAT anything to anything as long as you don't have overlapping address space in the end and both sides agree to the configuration.


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