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I have the following setup:

a) a single-homed machine, A, that can see the Internet.

b) other machines B, C, and D that cannot see the Internet.

c) A, B, C, and D can see each other.

d) all machines are running either RHEL 5.3 or Fedora 16.

Question: Is it possible to have B, C, and D share the Internet connection with A somehow? Note, again, that machine A does not have a second NIC installed. (The solutions that I am finding on the Net assume A to be a dual-homed system!)

Also, could you please recommend a set of book(s) or online resources for a current and in-depth coverage of iptables for people with only a basic knowledge of TCP/IP?

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How does A see the Internet if it's single-homed? How do B, C, and D get assigned IP addresses? – David Schwartz Jun 11 '12 at 9:28
Well, A is itself using NAT: A's IP address is a private/internal IP address 192.168.x.y. Using an iptables technique not known to me, our Sys Admin has allowed Internet to be accessible from A. But he is not allowing Internet accessibility on B, C, and D for some really childish 'reasons' (I believe, his intention is usually to make my life difficult). Now, just like 2 or more virtualbox based VMs can see Internet via their host OS, I would like B, C, and D (which are real machines) to be able to reach the Internet via A. All machines have DHCP-assigned private IP addresses. – Harry Jun 11 '12 at 15:40
Is this a decision the sys admin has the authority to make? – David Schwartz Jun 11 '12 at 16:15
Yes. Such decisions are completely at his whim. – Harry Jun 12 '12 at 0:48

The answer lies within your router's capability.

You could use a DMZ for computer A and then firewall off all internet access to B,C,D - however A would not be accessible from b,c,d - it would be totally separate - and a DMZ will make computer A more visible to the internet than before.

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I vaguely recall picking up some chatter on iptables's ability to copy packets, 'NAT them', and then send them out via the same NIC... all without requiring a second NIC. Anything possible along these lines? Also, I'm wondering how do virtual machines (which would be B, C, and D) running on a host OS (which would be A, in the setup of this problem) accomplish this without requiring a second NIC. – Harry Jun 11 '12 at 10:27
I'm not exactly sure about that sort of thing and I don't want to spread misinformation. IPv6 is here (sorta) and will have an effect on the way things operate behind routers. That's where I would start my search at. – FEA5T Jun 13 '12 at 7:43
IPv6 is not an issue right now. – Harry Jun 14 '12 at 0:50
I mention IPv6 because I think it could solve your issue. – FEA5T Jun 14 '12 at 3:38
Could you elaborate just a little bit more on how IPv6 could solve my issue? – Harry Jun 15 '12 at 0:39

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